United States      Industrial Environmental Research  EPA-600/7-79-065
Environmental Protection  Laboratory          February 1979
Agency        Research Triangle Park NC 27711
Proceedings: Advances
in Particle Sampling
and Measurement
(Asheville, NC, May 1978)

Interagency
Energy/Environment
R&D Program  Report

-------
                  RESEARCH REPORTING SERIES


 Research reports of the Office of Research and Development, U.S. Environmental
 Protection Agency, have been grouped into nine series. These nine broad cate-
 gories were established to facilitate further development and application of en-
 vironmental technology. Elimination of  traditional grouping was consciously
 planned to foster technology transfer and a maximum interface in related fields.
 The nine series are:

     1. Environmental Health Effects Research

     2. Environmental Protection Technology

     3. Ecological Research

     4. Environmental Monitoring

     5. Socioeconomic Environmental Studies

     6. Scientific and Technical Assessment Reports (STAR)

     7. Interagency Energy-Environment Research and Development

     8. "Special" Reports

     9. Miscellaneous Reports

 This report has been assigned to the INTERAGENCY ENERGY-ENVIRONMENT
 RESEARCH AND DEVELOPMENT series. Reports in this series result from the
 effort funded under the 17-agency Federal Energy/Environment Research and
 Development Program. These studies relate to EPA's mission to protect the public
 health and welfare  from adverse  effects of pollutants associated with energy sys-
 tems. The goal of  the Program is to assure the rapid development of domestic
 energy supplies in  an environmentally-compatible manner by providing the nec-
 essary environmental data and control technology. Investigations include analy-
 ses of the transport of energy-related pollutants and their health and ecological
 effects; assessments  of, and development of, control technologies  for  energy
 systems; and integrated assessments of a wide  range of energy-related environ-
 mental issues.
                        EPA REVIEW NOTICE
This report has been reviewed by the participating Federal Agencies, and approved
for publication. Approval does not signify that the contents necessarily reflect
the views and policies of the Government, nor does mention of trade names or
commercial products constitute endorsement or recommendation for use.

This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.

-------
                                     EPA-600/7-79-065

                                          February 1979
Proceedings: Advances in Particle
    Sampling and Measurement
           (Asheville, NC, May 1978)
                     W.B. Smith, Compiler

                   Southern Research Institute
                   2000 Ninth Avenue, South
                   Birmingham, Alabama 35205
                    Contract No. 68-02-2131
                      Task No. 21306
                   Program Element No. INE623
                 EPA Project Officer: D. Bruce Harris

               Industrial Environmental Research Laboratory
                Office of Energy, Minerals, and Industry
                  Research Triangle Park, NC 27711
                       Prepared for

               U.S. ENVIRONMENTAL PROTECTION AGENCY
                 Office of Research and Development
                    Washington, DC 20460

-------
                              PREFACE
     The Symposium on Advances in Particle Sampling and Measure-
ment held in Asheville, NC, May 15-17, 1978, was sponsored by
the Process Measurement Branch, Industrial Environmental Research
Laboratory, U.S. Environmental Protection Agency.  D. Bruce
Harris, EPA, served as symposium chairman.  Session chairmen
were A.R. MacFarland, Texas ASM University; Dale Lundgren, Uni-
versity of Florida; W.B. Kuykendal, EPA; T.T. Mercer, University
of Rochester; and G.B. Nichols, Southern Research Institute.

     A list of  reports on  the  research  supported by  the Process
Measurements Branch  can be obtained  from Mrs. Judy Ford, MD-62,
Process Measurements  Branch, Industrial Environmental Research
Laboratory, U.S. Environmental Protection Agency, Research
Triangle Park,  NC  27711,
                               111

-------
                             ABSTRACT


     The proceedings consist of 17 papers on improved instruments
and techniques for sampling and measurement of particulate emis-
sions and aerosols.  Cascade impactors are described with low-
pressure stages that extend the useful range of these sampling
devices down to 0.02 ym?  their use in measuring particle size
distribution of fly ash  from coal-fired boilers and in testing
a smoke suppressant in a gas turbine is described.  A new empiri-
cal equation simplifies  calibration of cyclone collectors used
for sampling aerosols.   Diffusion battery-nuclei counter com-
binations can be  used for  automatic monitoring of particle-size
distribution and  number  concentration of ambient aerosols.  Trans-
missometers and instruments for measuring scattered light were
compared over a one-year period for continuous monitoring of
stack emissions at a secondary lead smelter.  Instruments for
measuring electrical charge transfer and beta radiation attenua-
tion were less reliable  in this use.  A laser light back-scattering
instrument was compared  in pulp and paper mills against a trans-
missometer in continuous monitoring of emissions from a wood-
waste fired power boiler,  a kraft recovery  furnace, and a lime
kiln.  Other papers discussed a computer-based, data reduction
method for plotting curves of particle size distribution; tech-
niques and equipment  for generating monodisperse aerosols and
their use  in calibrating instruments; guidelines in selecting
laboratory methods  for particle sizing; minimizing weight changes
in  impactor collection substrates due to heat and sulfur oxides;
spectroscopic methods  for determination of  trace elements in
fly ash and their valence states; and sampling errors due to
aerodynamic effects.  Applications of improved sampling and
measurement techniques to the evaluation of emission control
devices include a wet  impingement technique for measuring par-
ticle sizes in wet  scrubbers; the use of real-time aerosol  in-
struments  in studying  the dynamic behavior  of baghouses; and
the measurement of  fractional collection efficiency of electro-
static precipitators  for particles 0.01-10  ym in diameter,  en-
abling the detection  of  transient fluctuations such as rapping
reentrainment of  fly  ash.
                               IV

-------
                             CONTENTS


Preface	.	iii
Abstract	iv
List of Speakers and Chairmen	vii

Paper 1.  Inertia Effects in Sampling Aerosols
C.N. Davies and M. Subari	    1

Paper 2.  Cyclone Sampler Performance
Morton Lippmann and Tai L. Chan	30

Paper 3.  Research on Dust Sampling  and Measurement in our
  Laboratory
Koichi linoya	52

Paper 4.  Sizing Submicron Particles With a Cascade
  Impactor
Michael J. Pilat.	74

Paper 5.  Experience in Sampling Urban Aerosols With the
  Sinclair Diffusion Battery and Nucleus Counter
Earl O. Knutson and David Sinclair	98

Paper 6.  Selecting Laboratory Methods for Particle
  Sizing
Ronald G. Draftz	121

Paper 7.  Long Term Field Evaluation of Continuous
  Particulate Monitors
A.W. Gnyp, S.J.W. Price, C.C.  St.  Pierre, and D.S. Smith.  .  .  122

Paper 8.  An In-Stack Fine Particle  Size Spectrometer:
  A Discussion of its Design and Development
Robert G. Knollenberg 	  169

Paper 9.  Optical Measurements of  Particulate Size in
  Stationary Source Emissions
A.L. Wertheimer, M.N. Trainer, and W.H. Hart	195

Paper 10.  Studies on Relating Plume Appearance to
  Emission Rate and Continuous Particulate Mass
  Emission Monitoring
K.T. Hood and H.S. Oglesby.	211
                               v

-------
Paper 11.  A Data Reduction System for Cascade  Impactors
J.D. McCain, G. Clinard, L.G. Felix, and J. Johnson  	  228

Paper. 12.  Aerosol Generation and Calibration of
  Instruments
David Y.H. Pui and Benjamin Y.H. Liu	  .  260

Paper 13.  Substrate Collectors for  Impactors -
  An Evaluation
D. Bruce Harris, G. Clinard, L.G. Felix, G. Lacey,
  and J.D. McCain	„  .  293

Paper 14.  Particle Size Measurement for the Evaluation
  of Wet Scrubbers
Seymour  Calvert, Richard Chmielewski, and  Shui-Chow  Yung.  „  .  301

Paper 15.  Evaluation  of Performance and Particle  Size
  Dependent  Efficiency of  Baghouses
D.S. Ensor,  R.Go Hooper, G. Markowski, and R.C. Carr.  ....  314

Paper 16.  Evaluation  of the Efficiency of Electrostatic
  Precipitators
Wallace  B. Smith,  John P.  Gooch, Joseph D.  McCain,
  and James  E. McCormack.  ..........  	  337

Paper 17.  Some  Studies of Chemical  Species in  Fly Ash
L.D. Hulett,  J.F.  Emery, J.M, Dale,  A.J. Weinberger,
  H.W. Dunn,  C.  Feldman, E. Ricci, and J.O. Thomson  	  355

Summary.  Advances  in  Particle  Sampling and Measurement
William  Farthing	  372

Metric Conversion  Factors  	  ............  380
                                VI

-------
                      SPEAKERS AND CHAIRMEN
Mr. Richard Chmielewski
APT, Incorporated
4901 Morena Boulevard
Suite 402
San Diego, CA  92117
Phone:  714/272-0050

Dr. C.N. Davies
Department of  Chemistry
University of  Essex
Wivenhoe Park
Colchester C04 3SQ
ENGLAND
Phone:  Colchester 44144
   (STD Code 020 6)

Mr. R.G. Draftz
IIT Research Institute
10 West 35th Street
Chicago, IL 60616
Phone:  312/567-4291

Dr. David S.  Ensor
Meteorology Research, Inc.
464 West Woodbury Road
Altadena, CA 91009
Phone:  213/791-1901
Dr. Alec Gnyp
Department of Chemical
  Engineering
University of Windsor
Windsor, Ontario N9B3P4
CANADA
Phone:  519/253-4232
Mr. D. Bruce Harris
Environmental Protection
  Agency
Industrial Environmental
  Research Laboratory
Mail Stop MD-62
Research Triangle Park, NC
  27711
Phone:  919/541-2557-8


Mr. Kenneth T. Hood
NCASI, Engineering Experiment
  Station
Oregon State University
Corvallis, OR 97331
Phone:  503/754-2015

Dr. Lester D.  Hulett
Oak Ridge National Lab
4500 North E-10
Oak Ridge, TN 37830
Phone:  615/483-0155


Dr. Koichi linoya
Department of Chemical
  Engineering
Kyoto University
Kyoto
JAPAN
Dr. Robert G- Knollenberg
Particle Measurement Systems
1855 South 57th Court
Boulder, CO 80301
Phone:  303/443-7100
                               VII

-------
Dr. Earl Knutson
Health & Safety Lab
U.S. ERDA
376 Hudson Street
New York, NY 10014
Phone:  212/620-3655

Mr. W.B. Kuykendal
Environmental Protection Agency
Industrial Environmental
   Research Laboratory
Mail Stop MD-62
Research Triangle Park, NC
   27711
Phone:  919/541-2557

Dr. Morton Lippmann
Institute of Environmental
   Medicine
New York University Medical
   Center
New York, NY 10016
Phone:  212/679-3200

Dr. Dale Lundgren
Environmental Engineering
   Department
University of Florida
410 Black Hall
Gainesville, FL 32611
Phone:  904/392-0846

Mr. Joseph D. McCain
Southern Research Institute
2000 Ninth Avenue, South
Birmingham, AL 35205
Phones  205/323-6592,
   extension 278

Dr. Andrew R. McFarland
Civil Engineering Department
Texas A&M University
College Station, TX 77843
Phones  713/845-2241
Dr. Thomas T. Mercer
University of Rochester
Rochester, NY 14642
Phone:  716/275-3821


Mr. Grady B. Nichols
Southern Research Institute
2000 Ninth Avenue, South
Birmingham, AL 35205
Phone:  205/323-6592,
  extension 361

Dr. Michael Pilat
Air Resources Engineering
University of Washington
Seattle, WA 98195
Phones  206/543-4789

Dr. David Pui
Mechanical Engineering
  Department
University of Minnesota
Minneapolis, MN 55455
Phone:  612/323-2815
Dr. Wallace B. Smith
Southern Research Institute
2000 Ninth Avenue, South
Birmingham, AL 35205
Phone:  205/323-6592,
  extension 520
Dr. Allen Wertheimer
Leeds & Northrup Company
Dickerson Road
North Wales, PA 19454
Phones  215/643-2000,
  extension 493
                               viii

-------
                              PAPER 1



               INERTIA EFFECTS IN  SAMPLING AEROSOLS
                            C.N. DAVIES
                             M. SUBARI
                      DEPARTMENT OF CHEMISTRY
                        UNIVERSITY OF ESSEX
ABSTRACT
     A study is made of the aspiration coefficient of orifices
sampling aerosols, starting with a point sink and proceeding
to a tube of finite diameter.  A critical analysis is made of
previous work and new experimental results are presented for
sampling at 90° yaw with a sharp-edged tube.

INERTIALESS PARTICLES

     The trajectories of particles suspended in moving air may
differ from the streamlines of air flow either if their rate
of fall due to gravity is appreciable, compared with the air
velocity, or if the particles are sufficiently heavy to persist
in their original direction to some extent when the air flow
changes direction (Albrecht,1 Sell 2).  Measurements of the
concentration of particles, by sucking a known volume of aerosol
and assessing the particles in it, are liable to error because
of these gravitational and inertial effects.

     Consider, first, inertialess particles.  These can be de-
fined as having a stop-distance, ds, at the local air velocity,
u, which is small compared with the distance, &, from any bound-
ing solid surface.  That is

                    d  = TU « l                               (1)
                     s
where T is the relaxation time of a particle and is equal to
the mass divided by the aerodynamic drag at unit velocity.  Such
particles can still fall at an appreciable velocity, this being

                    v  = rg.                                   (2)
                     o

-------
     Inertialess particle systems therefore have  small  TU  and
large Jl,  but the limiting size of the Stokes number of  the sys-
tems,

                    Stu = TU/& « 1                            (3)

depends on the value of Stu, being lower for high values of vs/uf
hence both Stu and vs/u need to be considered  in  deciding  whether
a particle is inertialess and, of course, since u varies from
point to point in a flow field the particle may be  inertialess
while it is in some parts of the field but not so in  others.

     The sampling of inertialess particles with an  isolated small
tube yields accurate results (Davies3).  When  the airflow  ap-
proximates to ideal flow (potential or irrotational)  the par-
ticles themselves trace out a potential flow pattern,  the  concen-
tration of particles is the same at all points along  a  particle^
trajectory and trajectories do not intersect  (Walton1*;  Robinson  ;
Levin6) .

     There are two reasons why this does not mean that  a sampling
orifice will always take a perfect sample of  inertialess par-
ticles.

     Firstly, the velocity of the particles entering  the orifice
may  not be the same as the air velocity, V, in the  orifice.
Suppose that the normal to the plane of the sampling  orifice
makes an angle \p with the vertical.  Then the  velocity  with which
particles enter the orifice, resolved along the normal  is

                    V + v  cos ty                               (4)
                         s

Hence the concentration, c, calculated from the catch of par-
ticles  (including those stuck on the internal  surface of  the
orifice) and the volume of air sampled, is related  to the  true
concentration, c0, by

                    cV = c0 (V + vg cos 4>)                      (5)

The  efficiency of sampling or the aspiration  coefficient  of the
orifice is then, for inertialess particles,

                    A = c/c0 =  (V + vo cos 40/V                (6)
                                     S
Hence when 41 = 0 and the orifice faces upwards, A = 1 + vs/V
and  when \p = IT, with the orifice facing downwards,  A = 1  - vs/V.
Only when the plane of the orifice  is vertical and  ty = ir/2 is
a  true sample obtained.

     The other factor causing error  in the sampling of inertia-
less particles is the existence of dust shadows.   These regions

-------
free from particles exist below and downwind of objects placed
in an aerosol.  The effects are negligible  in  the  case of  a  small
tube, but a bulky sampling head creates a shadow which sometimes
reduces the aspiration coefficient of  its sampling orifice.
The writer has described the general effects  (Davies7»8'9).

     When the orifice  in an isolated head faces upwards it always
has A > 1; at low rates of suction in  calm  air a dust shadow
exists below the head  and particles settle  upon the  top, around
the orifice,  with  increasing  aspiration rate  the  shadow region
climbs up over the  top of the  head so  that  particles settle  only
upon a decreasing area around  the orifice.

     With an orifice in the under side of the  head,  in calm  air,
no particles enter  until a certain rate of  aspiration is attained;
increasing above this  value gradually  raises  the value of  A  until
it reaches unity at an infinite rate of suction.   As A increases
there is no change  in  the deposition of particles  on top of  the
head.  In a cross wind particles enter the  head at a lower suc-
tion rate than is the  case for calm air.  The  value  of A remains
higher than the value  for calm air, as suction is  increased,
but  the difference  decreases until they become the same at a
fairly high rate of suction.

     Dust shadows can  reduce A when the orifice is not isolated,
even when its plane is vertical, if it is in  the lee of an ob-
stacle; they may also  affect the sampling of particles with
inertia  (Davies  ).

     Since the concentration of inertialess particles is constant
along all trajectories, the values of  A which  are  less than  unity
result not from the aspiration of reduced concentrations but
because some of the particle trajectories which enter the  orifice
originate from boundaries inside dust  shadows  and  therefore  have
zero concentration  at  all points along their  lengths.  This  was
shown clearly by Walton1* who considered tubes  of flow of inertia-
less particles, particularly in elutriators.

PARTICLES WITH INERTIA; POINT  SINK

     The trajectories  of particles with inertia do not form  a
system with a velocity potential; the  concentration  may vary
along a trajectory  and trajectories may intersect  (Voloshchuk
and  Levin11).  A true  sample can still be obtained,  when par-
ticles exhibit unlimited inertia, if their  rate of fall under
gravity is negligible  and if the air movement  is solely due  to
aspiration into a point sink.  The concentration builds up as
the  orifice is approached, due to the  particles lagging behind
the  air flow, and the  analogue of a space charge around the  ori-
fice is formed.  Particles enter the orifice  with  a  reduced  ve-
locity which compensates for the excess concentration and  a  true
sample with A = 1 results  (Davies   12).

-------
     If the symmetry of this  "space charge"  is  sufficiently
destroyed by wind, or by the  settlement of particles  under  grav-
ity, the aspiration coefficient of the sampling  orifice  is  re-
duced.

     Levin6 has  shown how  particles which  have  very limited inertia
behave when approaching a  point  sink  when  they  are sedimenting
under gravity  and  there is a  wind.

      In order  to understand his  paper it  is  best to start with
the  equations  for  inertialess particles.   His equations  are
similar to  those of  Davies3 but  are  in polar coordinates.  A
great simplification  of the equations was  achieved by using as
x-axis the  direction  of the vector  sum of  the wind velocity,
W,  and the  sedimentation  velocity of  the  particles, vg.   This
sum has magnitude

                     u0 =  (W2  + v  2  +  2Wv   cos <|>)^             (7)
                                 S      S

where $ is  the angle  between  W and  vs.

      Since  the particles  are  inertialess,  the equations  for the
trajectories  are the  same  as  those  for the streamlines of flow.
The sink  sucks with  flow  Q and creates radial velocities -  Q/4Tir2
to  which  must  be added the radial resolutes  of  u0.  Hence the
equations for  radial  and  tangential  resolutes of a trajectory
are

                     u =  - Q/4irr2 +  u0 cos 6
                                              ;                 (8)
                     u =  - u0 sin 9

      By putting

                     H20   =  Q/47TU0                               (9)

      these  are rendered dimensionless,

                     ur/u0  = - A 02/r2  + cos 6
                                                              (10)
                     4 /ii .  = — cinfl          I

      The solution of these equations is

                    (r2/2&02) sin2 6 + cos 9 = K              (11)

 where K is constant along  a streamline or an inertialess trajec-
 tory.

      The formulation of these equations is shown in Figure 1.
 Note the direction of the  x-axis about which all trajectories

-------
                                                       1
            Figure 1. The coordinate system. A sink at 0 draws a flow Q.
                   The curve with asymptote 2 at x/£0 = -°° is a critical
                   trajectory with stagnation point of both air flow and
                   particle motion at S.
                                          x/C0
are symmetrical.  The  figure shows a meridian section and  the
critical  trajectory  through the stagnation  point, S, where
 u  =
  r
                            8
                              = 0
(12)
      It  is necessary  to  locate the critical trajectory  for  the
calculation of the aspiration coefficient  (Davies3).  The  equa-
tion  of  the critical  trajectory is
     or
/r2/2fce2J  sin2  6  +  cos 6 = 1

 r/Jl0 = I/cos (e/2)
                                                                 (13)
     All  particles with  trajectories between the critical  tra-
jectory and the x-axis enter the orifice;  none of those  outside
do so-  The critical  trajectory has the  asymptote at x = -« (0


                     yoo/Ao  = 2,                                 (14)

hence, the  rate of entry of particles  into the sink is

                     TT  (4fc2)  c0u0 = Qc0                         (15)

by equation (9), so that A = 1.

-------
     The critical  trajectory meets  the  x-axis at the stagnation
point, S, where 6=0,  y=0,  r=x and
                     x  /ft0  =  1                                 (16)
                      S
     When the particles  have  inertia it is necessary to consider
their acceleration  in  order to write down the dynamic equations:

m  (dv /dt - VQ ae/dt)  =  6TTan  (-Q/4irr2  + Uo cos 9 - v )
     re                                       r
m  (dv /dt + v  dO/dt)  =  Siran  (- u0  sin 6 + v_)
     y       r                               o
where vr and VQ  are the  radial and  tangential resolutes of par-
ticle velocity.   The equations are  rendered dimensionless by
dividing through by Girari •  ua and reducing t to dimensionless
t' and r to dimensionless r', so that

                     t  =  t1  JU/Uo and r = r1 fi,0

     Since T = m/Girar), equations (17)  in dimensionless form be-
come
                 '/dt1  -  v.'-ae/at1)  = -i/r|2  + cos e - v '
                r          6        /                      r    (19)
                     1  - v^-de/dt'J  = - sin 0 + VQ '

where  equation  (9)  shows that the dimensionless scale factor,
      TU0/J,0  =  TUO  ^/4Tru0/Q = T V4TTu73/Q = k                 (20)

      By integrating these equations the particle velocity  (vr,
 VQ)  can be obtained at all points along a trajectory.  Levin6
 succeeded in obtaining solutions as series of rising powers of
 k,  for  small values of k, by assuming that a particle stagnation
 point existed  at S, in the same position as the air velocity
 stagnation point.   At S, and nowhere else, both particles  and
 air  have zero velocity.  This is justifiable for small values
 of  k, since continuity must exist between air streamlines  and
 particle trajectories as k tends to zero.  When k = 0 equation
 (19)  reduces to equation (10) .
      His solutions are


      V  = cos 6 - 1/r" + k
                .2 + ,  I2(l-r'2 cos 6)
                                   r
                 3(1-3 cos2 6)  ,  20 cos 9 _ -, . ,  , & \  ,
                       r • t     "*"     ,6       '    J    	

                                                   4 sin  91 ,
                                                   	T~l+  ' • •
                                                       r'6  )
v. = _ sin e - k SJJLJ. _ ka J6 sin  9 cos  6
 9                 .-1 3
                                                               (21)

-------
When k = 0 these equations reduce  to  equation  (10) .   They include
powers of 1/r ' = &0/r up to  the sixth;  since A0/r  =  1 at the
stagnation point, the trajectories are  increasingly  accurate
for greater distances from the sink.  This  is  important since
the calculation of the aspiration  coefficient,  A,  depends on
the value of  y at r = °°, 6 = IT  (equations  (14),  (15)).

     In order to obtain the  trajectory  equations  it  is  necessary,
as in integrating equation (10) , to substitute  in

                    dr/rde = v /VQ                            (22)
                              r  W
from equation (21) and perform the integration.   It  is  not clear
how Levin proceeded at this  point  but he obtained  the asymptote
(r = oo) of the critical trajectory by successive  approximation,
starting with the equation (13) for k = 0.  This  gave,  in place
of (14), the  formula

                   (yoo/S-°)   = 4 -  3.2 k + 0.32  k2             (23)

Hence, since
then, using  (9)

                    A =  1 -  0.8  k +  0.08  k2                   (24)

     By comparing this with  the  results of numerical  integrations
of equations  (19) , Levin6 concluded  that  the error  in A, as given
by (24)  was not more than 1% when k  = 0.25 and not  more  than
2.5% when k = 0.5.  It will  be seen, later, that equation  (24)
is not valid up to such  large values of k as Levin  claimed.

     The writer  (Davies12) made  an analysis of the  behavior of
particles with inertia approaching a point sink  in  otherwise
calm air.  In the absence of appreciable  rate of fall,  series
solutions of the dynamic equations were obtained for  large and
small inertia and connected  by interpolation.  This gave the
distribution of concentration in the spherical "space charge"
region near the orifice.  Stepwise solutions, when  the particles
were also falling under  gravity, showed that some particles de-
scribed orbits about the sink.   The  calculations were made for
the condition

                    vs/V0 =  1                                 (25)

where               VQ = 1/T (QT/4TT)1/3                       (26)

was later defined as the dynamic sampling velocity  (Davies,11*
1968) .  This particular  formulation  arose because the dynamical
equations were rendered  dimensionless by  measuring  lengths  in

-------
units of the stop distance at velocity V  , and  times  in  units
of the particle relaxation time, t; hence

                    V0 = ds/T                                 (27)

     In order to compare these results with  those of  Levin  it
is necessary to convert from Davies1 system  to  Levin's.   This
is easily done.  Since u  = vs  (W  = 0), we have from  (26),  (29)
and  (20)


     Vs/VQ = TUJQT/47I)-1/3 =  (TU/fi,)2/3  = k2/3               (28)

Hence the condition  (25) also means that  k = 1.

     This of course  is far outside the limit for Levin's results
and  explains why his particles did not execute  orbits around
the  sink.

     Davies found that the limiting trajectory  failed to complete
an orbit while trajectories outside the limiting one  did not
orbit at all.  On this limiting  trajectory the  aspiration coef-
ficient was estimated to be 0.37.  For k  = 1, Levin's series
(24) gives A = 0.28; naturally,  this is not  the correct  value,
since k is too large; in fact, for slightly  larger  values of
k the series  (24) gives negative values of A.

     The value A = 0.37 for vs/V0  = k = 1 would be  correct  if
all  particles inside the critical  trajectory entered  the orifice,
even after orbiting.  However, it  is not  yet clear  whether  this
is true.  Davies found that a group of trajectories,  inside the
critical trajectories, completed closed orbits  and  then  escaped
from the sink.  If this is correct, the value of A  is reduced
from 0.37 to 0.23.   However, ter Kuile13  believes that all  tra-
jectories which execute orbits,  these being  inside  the critical
trajectory, must enter the sink.   He found that in  order to plot
accurate trajectories, a large number of  very short steps had
to be taken as the sink was approached and his  computer  program
was  designed to do this.  It is  possible  that the writer's  escap-
ing  particles only did so because  too few steps were  taken  along
the  trajectories and that they should really have been caught.
To settle the point, either more trajectories need  to be computed
or recourse made to  the theory of  central orbits.   Ter Kuile
and  the writer agree, when calculated on  the nearest  non-orbiting
trajectory to the axis of symmetry through the  sink,  on  the
assumption that all  orbiting particles enter, that  for vs/V0
= k  = 1, then A - 0.37.

     For heavy particles there  is  no stagnation point on the
x-axis, as was assumed by Levin  for k < 0.5.

-------
     It is important to notice  that Levin's  equation  (24)  is
derived by a theory in which  the effect  of the  inertia  of  the
particles is dominated by  their velocity of  approach  to the  vi-
cinity of the point sink;  this  velocity  is u0.   In  limiting  the
result to low values of k, he has eliminated the  influence upon
the value of A of the concentration "space charge"  around  the
sink and of particles with enough inertia to describe orbits
around the sink.  Because  of  this limitation,  it  will be seen
that decreasing the rate of suction, Q,  increases the value  of
k, equation  (20), so that  the aspiration coefficient, A, de-
creases.  Obviously this is because, when Q  is  small, more par-
ticles can shoot past the  sink, due to their inertia  upon  the
wind and sedimentation velocities.  This dependence of  A on  Q
was noted by Kaslow and Emrich,21 but its significance  was not
realized and some confusion was created.

     When inertia effects  are larger, inside Levin's  range,  those
due to the aspiration velocity  may preponderate and cause  a  re-
versal of the effect on A, so that increasing Q increases  the
sampling error.

     Confusion has also been  caused by a failure  to realize  that
particles with unlimited inertia have A  = 1  if  the  wind and  sedi-
mentation velocities are both negligible. Examples of  error
on this account are seen in the work of  Kaslow  and  Emrich,21
Kim,22 Pickett and Sansone,17 Breslin and Stein,15  Agarwal,19
Gibson and Ogden,16 and, no doubt, others.

PARTICLES WITH INERTIA; FINITE ORIFICE

     Levin's equation  (24) applies to a  point orifice.   He thought
that it could be used for  orifices of finite diameter,  D,  as
long as

                    D < 2A e.                                  (29)

This means that the radius is less than  the  distance, OS,  between
the orifice  and the stagnation  point  (16).

     A point sink has no orientation; on replacing  it by a finite
orifice the  direction of the  normal to the plane  of the orifice
introduces an additional variable.  For  simplicity, this will
be referred  to as the direction of the sampling tube, ip, as  shown
in Figure 2  relative to vs.   An independent  yaw angle,  relative
to W, will be considered later.

     Let W be the wind velocity, which is usually horizontal.
V is the mean air velocity in the sampling orifice  and  has the
direction of the sampling  tube-  Then

                    V = 4Q/7TD2                                (30)

-------
          Figure 2.  The additional angle, \jj, which is necessary in proceeding
                  from a point sink to a sampling tube of diameter D. Note
                  that the angles >|/ and $ are not necessarily in the same plane.
                  The angle of yaw between V and W is not shown.
                      Stw  =  TW/D,
      Two Stokes'  numbers  are involved, that  on the wind velocity

                                                                    (31)

and  that on the  sampling  velocity

                                                                    (32)
                      Stv  =  TV/D

      The magnitude of the  sum of  the wind  and sedimentation  ve-
locity  vectors  is u0  (equation 7),  as before, but,  from  (9)  and
(30)
                      *„  =  (D/4)
                                                                    (33)
and,  by (20),  (31),  (32),  (33),  and (7)

      k  = TU A   =  (4Tu  /D) */u  /V
                     V    o   /  "  o
                               ^
            oo
                  = 4Stw  (W/V)^  {l  + (vs/w)2  + 2 vg/W cos }3/*
                                                                    (34)
                                   10

-------
                = 4Stv{(w/v)
                        2(w/v)« (vs/v)cos }3/"

                                           (35)
Equation (35) is used when the wind velocity, W,  is small.

     Substitution  of  these values  of  k  in  equation (24)  gives
A = 1 -  3.2  Stw f _"
      W


   -fr
                    COS 
                                             V
             + 1.28 S


                  3/2
(I)
                                           2     cos
                                           (36)
or
A  =  1  -  3.2  St.
                  COS
(W
                                              WV
                                          +  2
                   1.28
                               COS
                                                        3/2
                                (37)
According  to  Levin,  the  limits  of  validity  of  these  equations,
which  in  fact are  overestimated, are
within  1%  for

within  2.5%  for
k = 0.25,

k = 0,5,
 A = 0.805

A = 0.62
                           (38)

                           (39)
      It  must  not  be  forgotten  that  another  angle,  that between
 the  sampling  tube and  the  vertical,  ty,  also has  to be allowed
 for.   The  values  of  A  in equations  (36)  and (37)  therefore need
 to be multiplied  by  the  factor  of equation  (6)  (see Figure 2).
 The  final  value becomes
  A
                            (Vv)
                COS
                                 (40)
     Note  that  the  terms  containing  vs  in equations (36)  and
 (37) express  the  loss  of  particles by the effect of sedimentation
 in causing  them to  shoot  past  the orifice,  whereas the vs in
 (40) expresses  the  loss or  gain  due  to  sedimentation in the plane
 of the orifice.   These equations do  not include losses due to
 distortion  of the symmetry  of  the concentration "space charge"
 or to orbiting  which come into operation at higher values of
 k.

     The value  of A for a sampling tube of finite diameter depends
 upon the yaw  angle  between  V and w.   This is not expressed by
 equations  (34)  to (37) which hold only  for very small values of
                                11

-------
k.  When V and W have the same or opposite  directions,  yaw is
0° or 180° and the concentration "space  charge"  is  symmetrical
about the sampling tube.  Changing  the yaw  to  90° destroys this
symmetry and will be accompanied by a decrease in the  value of
A.  Some experimental results at 90° yaw are described below.
When the sampling tube  is large there is a  possibility of  the
dust shadow reducing A  at 180° yaw.

THE DAVIES SAMPLING CRITERION

     The writer  (Davies1 "*) proposed that accurate samples  in
calm air would be obtained with an  isolated small tube, the words
"small tube" meaning that the aspiration coefficient is inde-
pendent of the orientation of the tube,  provided that

     5(QT/4ir)1/3 £ D/2  < 0.2{Q/irgT)J5                          (41)

     The right hand term represents a maximum  error  of ±4% under
the worst conditions, with the tube facing  up  or down  (i|j = 0
or IT, equation  (5)), due to sedimentation.

     The left hand term is derived  from  the excess  concentration
in the "space charge" region being  1.6%  at  a distance  of 5ds
from the center of the  orifice  (Davies12),  where, by (26)  and
(27)
                       =  (QT/47T)
                                 1/3
     Considering the gravitational condition,  use  of  equations
 (2) and  (30) shows that it makes

                    v /V < 0.04                               (42)
                     s

     The inertia condition reduces as  follows,  by  (30)  and (32) ,

                    5(D2VT/16)*/3 < D/2

     or             5D/2  st1/3 <  D/2                     (43)
     or             stv < 0.016

     When W =  0 and these values are  inserted  in  equation (37)
we obtain

                    A = 0.9996

Hence, in absolutely calm air, the  theoretical sampling  error,
according to Levin, is only 0.04% which  is  obviously  too strict
a criterion.   However, the important  effect of a  low  wind ve-
locity needs to be looked at.  Davies1 *  suggested that calm air
be defined as

                    W/V < 0.2                                 (44)

                               12

-------
     Note that the limited  size  of  orifice imposed by (29) re-
duces, by (33) to
                      u0/v)2  <  0.25                            (45)
and that the value of  u0/V defined  by (42)  and (44)  for all values
of  has
                     (u0/v)2  <  0.0576
so that Davies1  "small  tube"  is well  inside  Levin's maximum size,
(29).  Putting W/V = 0.2  into equation  (37)  gives  (W horizontal,
<|> = 90°)

     A = 1 - 3.2  (0.016)  (0.202 +  0.042)3/"  + ...

       = 0.995

showing an error  of 0.5%  due  to a  slight  ambient wind.   Great
care needs to be  taken  before relaxing  the criterion too much
since the wind error increases rapidly.   For example,  if W/V
= 0.5,

                    A = 0.982

and the error has increased nearly four times for  a two and half
times increase in wind  speed.

     If a 2.5% error is accepted as tolerable in "calm air",
that is for W/V  = 0.2,  then

                    0.975 =1-3.2 Stv (0.22 + 0.042)3/*

and

                    Sty = 0.085

     Substituting this  value  in  (41)  changes the original Davies
criterion to

                    2.87  (QT/4TT)1/3 * D/2 <  0.2 (Q/irgr) *      (46)
     For a 4%  inertial  error  at  W/V =  0.2,  Sty = 0.136.   This
matches the sedimentation  error  and the criterion becomes

                     2.45  (QT/4TT)1/3 <  D/2 < 0.2 (Q/Trgi) ^       (47)
In this case,  the  error  when  W =  V is 41%.   When W = 0.2V and
vs = 0.04V, with St  =  0.136,  the  criterion  (47)  makes A = 0.95.
                                13

-------
     The limit of W/V to which this can be extended while still
remaining within Levin's criterion  (29) requires

                    W/V < 0.5

With this value, and the factor 2.45 of (47) instead of 5, cal-
culating as in  (43) gives

                     (Sty/2)1/3 = 1/2.45 or Sty = 0.136

Hence, by (35)

                    k = 0.193

and by (24)

                    A = 0.85

which is within Levin's other limit of 1% error at k = 0.25,
(38).  When the wind is not horizontal, the value of A is raised.
However, the experiments described below indicate that Levin's
estimate of 1% error at k = 0.25 is far too low when applied
to a finite tube diameter.

     There are thus grounds for considering a change in the fac-
tor 5 of the inertial term of the Davies criterion to 2.45 so
that the new criterion is as in (47) , but lower values than this
will certainly involve larger errors.  (Figure 3)

     Several papers have been published in which the original
criterion is criticized as too severe.  The experimental tech-
nique in some has been inadequate and in all the importance of
the reaction of the wind speed and the sedimentation speed of
the particles upon the inertia effect has been entirely over-
looked, although it was emphasized by the writer12 and is  implicit
in Levin's equations (Figure 3).

EXPERIMENTAL RESULTS; CALM AIR

     A very careful series of experimental measurements is due
to Breslin and Stein1b (1975).  They measured aspiration coeffi-
cients with 398 < V < 5968 cm/sec and 0.04 < D < 0.4 cm, using
particles of coal dust with aerodynamic diameters between  2.9
and 41 ym.  By means of a Coulter counter, the dust counts were
broken down into 14 size ranges so that the disadvantages  of
employing an aerosol of wide size distribution were overcome.
Sampling was carried out with horizontal and vertical  (facing
upwards) tubes; in most of the latter experiments the gravita-
tional error due to settlement into the orifice  was small.  Many
experiments resulted in low values of A, down to 0.4.  The extra-
ordinary thing about these results  is that Breslin and Stein
operated with an ambient wind velocity averaging 20 cm/sec near

                               14

-------
     ^
     +
                                   (Stv/2)
                                       -1/3
         Figure 3. A/[1 + (vs/V)] cos $ as a function of f(W2 + Vs^J/V2]1/2 and
                (Sty/2)'1/3 according to equation (37) for horizontal wind.  The
                units on the axis of abscissae are (Stv/2)~1/3 since this is the  value
                of the constant multiplying the inertia term of the Davies sampling
                criterion.  The graphs enable the sampling error to be read off, for
                various values of (W2 + Vg2)/]/2 and vs/V, according to the value
                chosen for the constant, assuming that equation (37) is correct.

the  sampling points without realizing  that this  contributed very
much  to their values of  A;  in fact,  they actually  wrote  that
the  spread in their results "may  indicate that  the inertial
parameter alone  is not completely  adequate to characterize  aero-
dynamic effects  at sampling inlets".
      Their experimental  data are  plotted on  Figure 4,  the  aspira-
tion  coefficient,  as ordinate, against (Sty/2)"1/3 .   This  quan-
tity  is chosen  since it  is  equal  to  the  numerical  factor multiply-
ing  the left hand  term of  the Davies criterion,  namely  5 in the
original expression (41)  and now,  perhaps, reduced to 2.87  (46)
or 2.45 (47).   How this  comes about  can  easily  be  seen  from (43).
In these experiments vs/V was negligibly small  but W/V  ranged
from  about 0.05  to 0.004.   By inserting  these  values in equa-
tions (37)  the  two curves,  according to  Levin,  of  A against
                                   15

-------
(Stv/2)-1/3  have been plotted on Figure  4.   Most of the  experi-
mental  points fall between  these curves  and it is evident  that
the spread  of the values  of A as well as the low values  are en-
tirely  due  to the 20 cm/sec ambient wind.   If W = vs =  0 then
A = 1.   In  these experiments W » vs so  that the reduction of
A below unity was due to  W.  Once again,  it is the effect  of
W and vs  upon particles with appreciable inertia, which  causes
a reduction in A.  Particle inertia alone  does not affect  A for
isolated  orifices, as long  as the tube is  reasonably sharp-edged
and particles deposited on  the inner tube  wall are included in
the sample.   Note that Breslin and Stein use r0/ds, which  is
the same  as (Stv/2)-1/3,  and is the radius  of the sampling tube
divided by  the stop distance of the particles from velocity V0,
equations (26) and  (27) .
      Some experiments  have been performed by Gibson  and  Ogden;
 they did not attempt  to measure absolute concentrations  but
                                                                  i e
       i.o
       0.8
       0.6
       0.4
—    0.05  W/V
                                 (Stv/2)
                                     -1/3
      Figure 4. The experimental points of Breslin and Stein. ^ The two curves
             correspond to W/V = 0.004 and 0.05.  They illustrate the importance
             of the low ambient wind velocity of 20 cm/sec when the sampling
             velocity was 6000 and 400 cm/sec, respectively; vs/V was very small.
                                  16

-------
merely compared  individual  pairs of samples taken at differ-
ing values of Sty.  Sampling was  carried  out  with \p  =    =  0,
and W rarely exceeded 5 cm/sec.   Particle aerodynamic  diameters
were 9 to 39 pm.  Unfortunately  the experiments  were incorrectly
planned, the authors falling into the  old trap of failing  to
recognize that the  influences of  particle inertia and  of wind
plus sedimentation  are complementary.   In some pairs of  samples
the inertia ratio was high  and the  wind plus  sedimentation  ratio
was low; in others, the reverse  was true.   In fact,  without ex-
ception, the relative values of  each ratio were  such that  the
defect of the aspiration coefficient,  A,  in one  member of  a pair,
due to one cause, was almost exactly balanced by the defect in
the other member of the pair, due to the  other cause.  Calcula-
tion of the ratio of the values  of  A for  every pair  by equations
(37) and (40) shows that it should  be  within  1%  of unity in each
of the 26 pairs.  The experimental  ratios were between 0.51 and
1.15 and averaged 0,93, the differences from  unity being due
to experimental  error.

     Pickett and Sansone17  carried  out some experiments  On
sampling coal dust, comparing the distributions  of mass  with
particle size in samples taken with nozzles 0.2  cm square  and
1.3 cm diameter.  They failed to  detect any difference between
the mass distributions because most of the mass  of particles
collected was in sizes too  small  for the  sampling error  of  the
small orifice to be revealed; this  was pointed out by  Davies.18
Their criticism  of  the Davies criterion is invalidated by  in-
adequate experimental technique  and for the same reason  no  con-^
elusions can be  drawn, as was done  from the data of  Breslin and
Stein,15 about the  influence of  the ambient wind velocity.

     Agarwal19 also criticized the  criterion  but failed  to  realize
that the aspiration coefficient  is  a function of vs  of specific
form, for horizontal wind,  namely

                    A = f |stv|"(w2  + VS2)/V2~J3/*, vs/VJ       (48)

by equations  (37) and  (6).  Instead, he took  the product

                    Stv - vs/V =  Tvs/D

which is independent of V and is  obviously incorrect.

EXPERIMENTAL RESULTS - SAMPLING  IN  A WIND AT  90° YAW ANGLE

     Some experiments have  been  carried out in a small wind tun-
nel with the sampling tube  at right angles to the wind direction;
in some of the experiments  the wind was vertically downwards
so that $ =  0 and ^ = 90°.  In others,  the wind  was  horizontal,
making 4> = 90°,  and the sampling  tube  sucked  vertically  upwards
so that v> = 180°.
                                17

-------
     According to equations  (6) and  (37) ,  for values  of  A  near
to unity, the aspiration coefficients can  be calculated  from
the experimental data as follows, for comparison with the  actual
measured values of A.

     When  3/2
                                                      /W2+v 2\
                                          +1.28  Sty21   2  S I

                                                              (50)

     Provided that both vs/W and vs/V are small,  each case re-
duces to the same formula, namely

                       3/2                3
     A = 1 - 3.2 Stv(|)     + 1.25 Stv2(|)                    (51)

     Levin's equation  (24) relates to a point sink.  The object
of the experiments was to find out whether its adaption  to a
finite sampling tube in a given orientation, expressed by  equa-
tions (36)  and  (37), was  accurate.

     Nearly uniform particles of di-2-ethylhexyl  sebacate  (den-
sity 0.92 g/cm3) were produced by a spinning disc generator and
had diameters between 15  and 30 ym.  The wind speed, W,  could
be varied from 74 to 306  cm/sec and the suction speed, V,  from
188 to 2090 cm/sec.  The  sampling tubes had parallel bores with
thin walls tapering finely to a sharp edge at the orifice.   Bel-
yaev and Levin20 have shown that the use of a thick-walled tube
reduces A when sampling with <|> = ip = 90° at zero  yaw.

     The experiments were difficult to perform accurately  because
of fluctuations in the concentration of particles.  vs/W never
exceeded 1.8% and vs/V 0.72%, hence equation  (51) applies  for
each of the orientations  with an error which is barely percep-
tible in comparison with  the scatter of the results.  The  best
way of displaying the data is to plot the aspiration coefficient,
A, as a function of Stv  (W/V)3/2; according to equation  (51),
A should be a unique function of this variable.   The experimental
points are shown in this  way on Figure 5.

     Each sampling tube was attached to the second  stage of a
standard cascade impactor.  The particles deposited partly on
the inside of the sampling tube and partly on the cascade  im-
pactor plate, the aspiration coefficient being calculated  from

                               18

-------
      0.8
      0.6
      0.4
      0.2
                    .^^_ LEVIN'S THEORY, ADAPTED TO FINITE TUBE
                          DIAMETER, EQUATION (51)

                    O PATTENDEN AND WIFFEN23

                      DAVIES AND SUBARI, THIS PAPER
                       .O1
       0.01
                     0.1
                                  -W 1 3/2
       Figure 5. Experimental results for A as a function of Stv(W/V)3/2, sampling
              at 90° yaw angle with vs very small.

the sum of  those in the tube plus  those on the plate, divided
by the volume of air sampled.   The particles inside the tube
were estimated either by weighing  the  tube before and after de-
position or  by lining it with  thin metal  foil coated with a film
of magnesium oxide.  The airborne  concentration was measured
with a small isokinetic impactor,  facing  the wind, with a sharp-
edged slit  orifice.
     It  is
to include
particles
particles
some solid
bounce off
lets of  di
particles
incidence
     essential,  when measuring the concentration  of aerosols,
     particles  deposited inside the sampling  tube with
    collected on the impactor plate or  filter.   Liquid
    will usually adhere to the tube wall, on  impact, but
     particles,  especially at high rates of suction may
       In  the experiments now described the liquid drop-
    -2-ethylhexyl sebacate adhered to the metal tube, but
    which  struck the magnesium oxide layer at glancing
    often  rebounded and reached the sampling  plate.
     Ft  is  defined as the fraction  of  the total particles enter-
ing the  sampling  tube which were found  adhering to the wall of
the tube.   The experimental results are shown in Table 1.  Ft
could be calculated by the empirical formula
Ft = 7  1 +  erf
                            Stw  (W/V)
                                      0.2
                                0.15
                                                                 (52)
                                 19

-------
TABLE 1.  FRACTION Ft OF PARTICLES ENTERING THE SAMPLING TUBE
          WHICH DEPOSITS ON THE WALL OF THE TUBE

Method Stw
MgO 0.065
.065
.077
.077
.078
.078
.089
.089
.100
.100
.100
.100
.113
.160
.160
.160
.160
.178
.178
.178
.190
.190
.190
.190
.190
.204
.204
.220
.220
.220
w/v
0.093
.093
.110
.110
.400
.400
.400
.400
.150
.300
.400
.610
.400
.060
.120
.232
.470
.400
.400
.400
.070
.140
.270
.400
.530
.400
.400
.080
.170
.310
Ft
Calculated
0
0
0.001
.001
.009
.009
.023
.023
.013
.034
.048
.077
.094
.080
.155
.260
.404
.489
.489
.489
.202
.329
.472
.560
.622
.638
.638
.365
.532
.644

Experimental
0
0
0
0
0
0
0
0
0
0
0.10
.14
0
.05
.17
.18
.25
.29
.31
.27
.36
.31
.31
.58
.64
.53
.44
.43
.58
.61
                                                    (continued)
                              20

-------
                       TABLE 1 (continued)

Method St
MgO 0.240
.240
.256
.278
.278
.278
.290
.290
.346
.377
.377
.397
.397
.403
.462
.630
Weighing .630
.630
.630
.722
.722
.856
.856
.895
.895
W/V
0.351
.351
.400
.200
.400
.400
.475
.475
.400
.200
.200
.400
.400
.400
.400
.400
.200
.200
.400
.200
.400
.400
.400
.400
.400
Ff
Calculated
0.770
.770
.839
.798
.891
.891
.926
.926
.968
.955
.955
.987
.987
.989
.996
.999
.998
.998
.999
1.000
1.000
1.000
1.000
1.000
1.000

Experimental
0.75
.78
.81
.50
.54
.54
.92
.89
.85
.46
.57
1
1
.89
.87
1
1
1
1
1
1
1
1
1
1

and Table 1 shows that this agrees quite well with the experi-
mental measurements which cover the ranges 0.068 < St^ < 0.3
and 0.05 < W/V < 0.53.  Equation  (52)  is graphed in Figure 6
and has been extrapolated beyond  the experimental values to give
the curves up to W/V = 2.  This was done, as an interim measure,
to give warning of losses that can occur upon the tube wall.

                                21

-------
       0.8
       0.6
       0.4
       0.2
                 T     I   \   I  I  I I  I
                                   W/V    2  1 0.5|0.2 0.
        0.01
         Figure 6.  The fraction, Ft, of particles entering the sampling tube which
                deposits upon the inside of the tube (experimental data in
                Table 1).
     The experimental data, for each value  of  A measured, are
given in Table  2  and the results are plotted in  Figure 5, with
a separate point  for each experiment.  Also shown in Figure 5
are 14 points calculated from Table 2 of Pattenden and Wiffen's
paper23; each  is  the mean of about  four  measurements in  a wind
tunnel at wind  speeds between 2 and 6 m/sec,  using solid
particles with  aerodynamic diameters from  4.5  to 25 vim.  The
sampling tube was vertical, in a horizontal wind, and it made
no difference whether the tube pointed upwards or downwards,
hence vs was negligible; the tube diameter  was 1.25 cm,  its end
was cut off square and the wall thickness  was  about 0.2 cm.
The mean inlet  velocity was 70 cm/sec.   Only  their experiments
with a tube without a cover are discussed  here.   They found that
with a cylindrical rain cover over the tube there was a  substan-
tial increase in  the aspiration coefficient;  this is an  example
of May's stagnation point sampling, 2
-------
TABLE 2.  EXPERIMENTAL RESULTS

Series
Ai
Ai
Ai
A!
Ax
A!
Ai
A!
A!
A!
A!
A2
A2
A2
A2
A2
A2
A2
A2
A2
A2
A2
A2
BI
BI
BI
BI
BI
BI
BI
BI
B3
B3
Orientation
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
stv
0.70
.70
.70
.70
.70
.70
.70
.70
.70
.70
.70
1.35
2.7
1.35
1.35
2.7
.36
.47
1.35
.35
.17
.26
.35
.17
.17
.17
.27
.27
.31
.31
.31
.89
1.02
W/V
0.110
.110
.093
.310
.232
.270
.150
.475
.475
.351
.351
.17
.08
.14
.14
.07
.53
.40
.12
.47
.61
.40
.30
.2
.2
.2
.2
.2
.2
.2
.2
.2
• 2
vs/V
0.001
.001
.001
.001
.001
.001
.001
.001
.001
.001
.001
.001
.000
.001
.001
.000
.002
.002
.001
.002
.003
.002
.001
.0018
.0018
.0018
.0018
.0018
.0018
.0018
.0018
.0034
.0034
A
0.498
.515
.425
.433
.378
.500
.580
.287
.556
.566
.504
.346
.365
.324
.390
.358
.638
.446
.343
.361
.493
.586
.570
.786
.609
.687
.516
.547
.448
.507
.408
.354
.364
/W+v\3/2
Stv\ V /
0.026
.026
.020
.121
.079
.099
.041
.230
.230
.146
.146
.095
.061
.071
.071
.050
.140
.120
.057
.113
.082
.066
.058
.015
.015
.015
.024
.024
.028
.028
.028
.082
.094
                                    (continued)
               23

-------
TABLE 2 (continued)

Series
Ci
C2
C3
c.
c,
C*
c*
c,,
B3
B3
B3
B3
B3
B3
B3
B3
B.,
B*
B.,
B*
G!
Ci
Ci
Ci
Ci
Ci
Ci
Ci
Ci
Ci
Ci
G!
C2
C2
C2
C2
Orientation
V
V
V
V
V
V
V
V
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
stv
0.086
.28
1.43
1.43
1.64
1.64
2.234
2.238
.89
.89
1.02
1.02
1.39
1.39
1.89
1.89
3.15
3.15
3.6
3.6
.086
.086
.086
.086
.086
.136
.136
.136
.136
.155
.155
.155
.195
.195
.22
.22
W/V
0.4
.4
.4
.4
.4
.4
.4
.4
.2
.2
.2
.2
.2
.2
.2
.2
.2
.2
.2
.2
.4
.4
.4
.4
.4
.4
.4
.4
.4
.4
.4
.4
.4
.4
.4
.4
vs/V
0.0034
.0068
.0021
.0021
.0021
.0021
.0021
.0021
.0034
.0034
.0034
.0034
.0034
.0034
.0034
.0034
.0036
.0036
.0036
.0036
.0034
.0034
.0034
.0034
.0034
.0034
.0034
.0034
.0034
.0034
.0034
.0034
.0023
.0023
.0023
.0023
A
0.602
.368
.135
.178
.139
.32
.154
.238
.342
.310
.337
.334
.364
.488
.371
.359
.259
.349
.326
.274
.747
.600
.690
.718
.744
.390
.600
.686
.686
.346
.450
.600
.509
.417
.403
.306
/W+v\'/'
stv (—)
0.022
.073
.365
.365
.418
.418
.571
.571
.082
.082
.094
.094
.128
.128
.173
.173
.289
.289
.289
.289
.022
.022
.022
.022
.022
.035
.035
.035
.035
.040
.040
.040
. 050
.050
.057
.057
                            (continued)
        24

-------
                       TABLE 2 (continued)

Series
C3
C3
C3
C3
C3
C3
C3
C3
C3
cs
C6
C6
C6
C7
C7
C7
C7
C7
Orientation St
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
0.445
.445
.445
.51
.51
.69
.69
.28
-.28
.64
.865
.99
.99
1.01
1.16
1.58
1.58
1.81
W/V
0.4
.4
.4
.4
.4
.4
.4
.4
.4
.4
.4
.4
.4
.4
.4
.4
.4
.4
vs/V
0.0068
.0068
.0068
.0068
.0068
.0068
.0068
.0068
.0068
.0047
.0062
.0062
.0062
.0072
.0072
.0072
.0072
.0072
A
0.570
.512
.400
.475
.468
.581
.468
.520
.610
.645
.500
.331
.360
.151
.263
.183
.130
.160
/W+V\3/2
04. I = 1
btv\ v )
0.115
.115
.115
.132
.132
.180
.180
.073
.073
.165
.224
.256
.256
.262
.300
.409
.409
.469

     Also shown in Figure 5 is the line of equation  (51) as  far
as A = 0.62, which is Levin's limit for 2.5% error and  k = 0.5.
It is clear that this equation makes the value of A  too large
compared with the experimental results at 90° yaw.

     The results of Pattenden and Wiffen are in  rough agreement
with Ours up to Stv(W/V)3'2 = 0.9.  At this point their values
of A fall abruptly and maintain a low level, 0.05 to 0.08 for
0.13 St  (W/V)3/2 < 3.

     Since

                    Stv(W/V)3/2 = Stw(W/V)*                   (53)

the lower limit, 0.13, corresponds to
                    Stw = 0.13  (2.9)~35  =  0.08
and the higher to
                    Stw = 3  (8.6)~^  =  1.02

where their range of W/V was  from  2.9  to  8.6.

                               25

-------
     Looking at Figure 6, it  is clear  that  all  their  measure-
ments which give the low values of A were made  under  conditions
such that a large proportion  of the particles would be  likely
to stick to the tube wall and fail to  reach the filter.   It is
possible that their employment of a thick-walled,  blunt tube
had something to do with this.

     Instead of A falling at  an initial  rate corresponding to

                    A = 1 - 3.2 Stv(W/V)3/2  +  ...             (51)

it seems that the equation should be more like

                    A = 1 - 10 Stv(W/V)3/2  + ...              (54)

There are signs of minimum and maximum values of A at the ab-
scissae 0.8 and 0.16, respectively.  The temporary reversal of
the trend of A, between these values,  must  be due  to  a  change
in the mechanism of inertia effect, which was referred  to above.
Bearing equation  (53) in mind, the initial,  Levin  effect is due
to particles being whisked past the orifice and A  is  increased
if V is increased; however, at higher  values of St the "space
charge" effect comes in and A increases  as  V is decreased,  by
enough to give the small rise in A between  the  minimum  and
maximum.

     At still higher values of Stw and W/V  the  wind stream flow
tube has to expand considerably on entering the sampling tube
so that many particles  shoot  out of the  flow tube, due  to their
inertia, and A becomes  small.  This, actually,  is  a return to-
wards  the point  sink approximation.  An  increase  in W lowers
the ratio of the cross  section of the  wind  stream  flow  tube
to that of  the orifice  and A  falls; an increase in V  has
the opposite effect and A rises.

     Of course,  the tube diameter has  to be constant  during the
above  changes, but this  is looked after  by  the  Stokes numbers.

CONCLUSIONS

     Levin's equation for a point sink in a wind  (24)  can be
adapted for use  with sampling tubes of finite diameter  by in-
cluding as  variables the angle between the  tube axis  and the
vertical  (36, 37,  40) and the angle of yaw  between the  tube
axis and the wind  direction.

     His limits  (38, 39) overestimate  the accuracy of his equa-
tion,  when  adapted to finite  tubes, because his theory  takes
account neither  of the  ratio  of  the sedimentation  velocity of
the particles to the mean sampling velocity, nor  of  the effect
of inertial build-up of  concentration  near  the  orifice, or "space
charge" which, in  the presence of wind or sedimentation, may

                                26

-------
reduce A.  Levin's assumption  that  a  quadratic  function  of k
can represent A down to  0.62  (2.5%  error)  does  not  hold;  a more
complicated expression,  at  least  a  cubic,  is  necessary  in the
case of sampling at 90°  yaw angle.

     Quite low wind and  sedimentation velocities  have a  substan-
tial effect in reducing  A according to Levin's  theory.   That
they must be taken account  of  in  assessing sampling error is
clear from the work of Breslin and  Stein15 and  from our  own
experiments.  Arguing from  Levin's  equation (24)  adapted  to a
finite orifice  (36, 37), it is shown  that  the Davies sampling
criterion might be made  slightly  less restrictive for small tube
sampling with W/V < 0.2  by  using,  instead  of  the  original form
(41),

                    2.45 (QT/4TT)1/3 < D/2  < 0.2 (Q/Trgi)^,    (55)
which gives a maximum  error  of  about  5%  when  both  terms  have
the most unfavorable values.

     However, caution  is  necessary  because  the  inertial  term
is based on the  adaptation  (finite  orifice) of  Levin's equation,
which  tends  to
                     A =  1  -  3.2  f(Stv,  W/V,  v  /V) ,
                                     V        o
as  in  equation  (37),  whereas  the  experiments  suggest,  at  90°
yaw, that  the factor  is  10  rather than  3.2.   It  is  possible,
when Stv(W/V)3/2  is less than 0.01,  that  the  curve.actually de-
creases  its  slope and approaches  (A  =  1,  Stv(W/V)3/2  = 0)  with
the factor 3.2,  in which case the criterion  (55)  is correct.
Were the factor  to be greater than 3.2  the original form  of  (55),
namely (41)  might be  better.   Unfortunately,  it  is  very difficult
to  do  experiments at  small  values of Stv  and  neither  our  own
nor those  of Breslin  and Stein15  are sufficiently accurate and
numerous to  enable a  decision to  be  taken.   In place  of the 2.45
in  the criterion  (55)  they  suggest 1.5  at which  value their own
values of  A  range from 0.92 to 1.01  and an average  error  of 5%
might  be anticipated.   In any practical sampling system,  though,
the wind is  certainly not zero.   The writer's view  is that W/V
= 0.2  is a practical  figure for a "calm air"  situation and it
is  on  this that  (55)  was based.

     Our work shows that when St^ exceeds 0.08 an increasing
deposition takes  place on the inner  surface  of the  sampling tube,
and with St^ >  0.3 almost all the sample  will strike  the  tube
wall.  This  effect needs to be looked  after  in practical  sampling.

     It  is possible that impact on the  inside of the  tube is
affected to  some  extent  by  turbulence  in  the  wind stream.  A
study  is being made of the  way in which the  density of the deposit
is distributed  in the tube.   The  Reynolds number of the wind

                                27

-------
tunnel, which was a smooth circular duct 10 cm  in diameter,  ranged
from 5000 to 20,000.  The stop distance of the  particles on  the
wind velocity varied from 0.052 cm to 0.85 cm.

     Clearly the particles with the larger values of  stop-distance
would be little affected by turbulence and at low wind  speeds
there would not have been strong turbulence.  In the  intermedi-
ate ranges of particle size and wind speed some enhancement  of
deposition in the tube is possible but an appreciable effect
on the aspiration coefficient seems unlikely.

ACKNOWLEDGEMENTS

     The apparatus was built by Sarah Weedon and M.J. Farncombe
with the aid of a grant from the National Coal  Board.   Mr. M.
Subari developed the apparatus and performed all the  experiments.
He is grateful for financial support from the University of
Technology Malaysia, at Kuala Lumpur.

     The apparatus is designed for experiments  on the deposition
of particles between 2.5 and 15 ym aerodynamic  diameter in the
human respiratory tract.  Before this work could be started  it
was necessary to study the entry of particles into a  breathing
tube at 90° yaw angle to the moving stream of aerosol.  Applica-
tions for a grant to support the inhalation experiments were
made to the Medical Research Council and to the Directorate-
General, Employment and Social Affairs, of the  Commission of
the European Communities but were rejected, the latter  on the
grounds that no funds were to be provided for basic research.

REFERENCES

  1.  Albrecht, F.  Physik. Z. 32:48, 1931.

  2.  Sell, W.  VDI-Forschungsh. 347: 1, 1931.

  3.  Davies, C.N.  Trans. Inst. Chem. Eng. Suppl. 25:36, 1947.

  4.  Walton, W.H.  Br. J. Appl. Phys. Suppl. No. 3, S29, 1954.

  5.  Robinson, A.  Commun. Pure Appl. Math. 9:69, 1956.

  6.  Levin, L.M.  Izv. Akad. Nauk SSSR Ser. Geofiz. 7:914, 1957.

  7.  Davies, C.N., and V. Peetz.  Br. J. Appl.  Phys.  Suppl.  No.
     3, S17, 1954.

  8.  Davies, C.N.  Br. J. Appl. Phys. 18:653, 1967.

  9.  Davies, C.N.  Br. J. Appl. Phys. 18:1787,  1967.

10.  Davies, C.N.  Br. J. Appl. Phys. 11:535, 1960.

                                28

-------
11.  Voloshchuk, V.M., and L.M. Levin.   Izv.  Akad.  Nauk  SSSR
     Fiz. Atmos. Okeana 4{7):734,  1968.

12.  Davies, C.N.  Proc. R. Soc. London  Ser.  A  279:413,  1964.

13.  ter Kuile, W.M.  Rep. F.  1582.  Inst. Milieuhygiene  Gezond-
     heidstechniek. 1G-TNO, Delft,  1977.

14.  Davies, C.N.  Br. J. Appl. Phys.  (J. Phys.  D),  Ser.  2,  1:921,
     1968.

15.  Breslin, J.A., and R.L. Stein.  J.  Am.  Ind.  Hyg. Assoc.
     36:576, 1975.

16.  Gibson, H., and T.L. Ogden.   J. Aerosol  Sci.  8:361,  1977.

17.  Pickett, W.E., and E.B. Sansone.  J. Am. Ind.  Hyg.  Assoc.
     34:421, 1973.

18.  Davies, C.N.  J. Am. Ind. Hyg.  Assoc.  36(9):714, 1975.

19.  Agarwal, J.K.  Particle Technology  Lab.  Publication 265,
     Univ.  of Minnesota, 1975.

20.  Belyaev, S.P., and L.M. Levin.  J.  Aerosol  Sci.  3:127,  1972.

21.  Kaslow, D.E., and R.J. Emrich.  Lehigh Univ.,  Bethlehem,
     PA.  Dept. Physics Tech.  Rep.  23, 1973;  Tech.  Rep.  25,  1974.

22.  Kim, Y.W.  Lehigh Univ. Dept.  Physics  Tech.  Rep. 24, 1974.

23.  Pattenden, N.J., and R.D. Wiffen.   Atmos. Environ.  11:677,
     1977.

24.  May, K.R.  Physical Aspects of  Sampling.   In:  Airborne
     Microbes,  P.H. Gregory and J.L. Monteith, eds.  Cambridge
     Univ.  Press,  London, 1967.  pp. 60-80.
                                29

-------
                             PAPER  2


                   CYCLONE SAMPLER  PERFORMANCE
                         MORTON  LIPPMANN
                       NEW YORK  UNIVERSITY
                INSTITUTE OF  ENVIRONMENTAL MEDICINE

                               AND

                           TAI L. CHAN
               GENERAL MOTORS RESEARCH LABORATORIES
ABSTRACT
     Cyclones are finding increasing application in air sampling
both as pre-collectors in two-stage samplers and as stages  in
multi-stage samplers for size-mass distribution determinations.
They are well suited for both applications because of their  rela-
tively low cost, compact size, and independence of orientation
and loading conditions.  Their applications have been limited
primarily because they have required extensive empirical calibra-
tions.  A new predictive relation for cyclone collection effi-
ciency has been developed which permits extrapolation from  a
limited experimental data base to a wide variety of operating
conditions.  Constants for the equation are presented for eleven
small cyclones ranging in diameter from 10 to 152 mm.

INTRODUCTION

     Cyclones are devices which remove particles from fluid  streams
as  the stream is caused  to rotate within a cylindrical and/or
conical cross section.   A conventional cyclone design is illus-
trated in Figure 1.  Particles with sufficient momentum to  cross
the flow streamlines and reach the outer wall are arrested,  and
are either retained at the wall or migrate along the wall to
a collection zone at the bottom.  In hydroclones, which are
cyclones for separating  particles from aqueous suspensions,  a
small percentage of the  liquid effluent is withdrawn at the  bottom
with the collected particles.  The bulk of the liquid and the
undersized particles exit through the axial pipe at the top.
In  air cleaning and air  sampling cyclones, all of the air exits
at  the top.


                                30

-------
     Cyclones  are widely used for removing  particles of relatively
large size  from fluids because of their  relative simplicity and
relatively  low costs in terms of construction,  operation, and
energy consumption.   They are frequently used as a first stage
or pre-collector upstream of a particle  collector with a high
collection  efficiency for the small  particles not removed by
the cyclone.

     Most of the literature on cyclones  and their performance
relates  to cyclones used in cleaning of  fluid streams, and has
proven  to be,  unfortunately, of  relatively  little use in describ-
ing the  performance of cyclones  used in  air sampling applica-
tions.   The flow patterns and dust  loading  in the small cyclones
                                           MAIN VORTEX
                                           VORTEX CORE
           Figure 1. Conventional double vortex flow pattern found in air
                  cleaning cyclones (from Hochstrasser24).
                                 31

-------
used in sampling are generally  quite  different  from those  found
in air cleaning cyclones and  hydroclones.

APPLICATIONS OF CYCLONES IN AIR SAMPLING

"Respirable" Dust Sampling

     By far the greatest usage  of  small  cyclones in aerosol sampl-
ing has been as the  first stage of a  two-stage  sampler.   In most
cases, they have been  operated  at  flow rates which were  believed
to permit cyclone penetrations  equivalent  to the penetration
of inhaled dust to  the non-ciliated deep lung spaces in  humans.
Such applications have been called "respirable" dust sampling,
and their rationale  has previously been  discussed.1'2'3

      In  "respirable"  dust sampling, it is  essential that the
cyclone  cut-off characteristics be known and constant, and that
each  cyclone  be operated at a flow rate  which produces the de-
sired  cut-off.   In  the absence  of  a usable theory, it has been
necessary  to  design and calibrate  air sampling  cyclones  empiri-
cally.  Unfortunately, dependence  on  an  empirical calibration
can  lead to  controversy and errors.  The original calibration
of the Dorr-Oliver  10-mm nylon  cyclone1*  failed  to include an
 appropriate  aerodynamic shape factor.  With Kotrappa's5  shape
 factor correction,  the recommended sampling rate was reduced
 to 1.8 Vmin,  which is in good  agreement with most of the more
 recent empirical  calibrations,6'7'8'9'10 which  recommend either
 1.7  or 1.8  Vmin.   However,  the Mine  Safety and Health Adminis-
 tration, which specifies  acceptable samplers and their operating
 characteristics in  mine dust  evaluations,  still insists  that
 the 10-mm cyclone be operated at 2.0  &/min, on  the basis of its
 own calibration by  Tomb and  Raymond.11

      There are conflicting  calibration data for several  of the
 12.5 to 50-mm diameter stainless steel cyclones which have also
 been used for size-selective  sampling.  Some of the differences
 can be attributed to the  same causes  as for the 10-mm cyclone,
 i.e., differences in calibration techniques, data interpretation,
 and failure to use appropriate particle shape corrections.
 Another factor is the dimensional variations between nominally
 identical samplers which  were documented by Lippmann and Chan.12
 The steel cyclones are individually assembled,  and the quality
 control exercised by the  manufacturers has not always been ad-
 equate.  The 10-mm nylon  cyclones, which are injection molded,
 have not been observed or  reporter: to vary significantly from'
 one to another.

      The use of cyclones  as  the first stage in two-stage samplers
 for  "respirable"  dust sampling received its first major  impetus
 in the atomic industry when,  in January 1961, the U.S. Atomic
 Energy Commission's Office  of Health and Safety defined  "respir-
 able" dust as that portion  of the  inhaled dust which penetrates

                                32

-------
to the non-ciliated portions of the lung.  Further,  they defined
"respirable" dust specifically as  follows:
     Aerodynamic Diameter  (ym) :   >10.   5.   3.5   2.5   <2.0

     % Respirable:                  0    25   50    75     100


     A variety of commercially available small  cyclones were
found to have collection characteristics at appropriate flow
rates which were close  to  those  of  the  AEC  specification,* and
some of them were used  extensively  in sampling  programs by AEC
contractors.

     More widespread  application followed the decision of the
American Conference of  Governmental Industrial  Hygienists (ACGIH)
in 1968 to issue a Notice  of  Intended Change in the  threshold
limit value  (TLV) for quartz,  cristobalite, and tridymite (three
forms of crystalline  free  silica).13  The size-selection  charac-
teristics for the first stage  collector defined by ACGIH  were
identical to those of AEC,  except that  they specified that at
< 2.0 ym, the %  "respirable"  would  be 90% rather than 100%.
For all practical purposes,  the  two specifications are essentially
the same.

     In 1969, the Federal  Coal Mine Health  and  Safety Act speci-
fied a "respirable" dust limit for  coal mine dust, and all com-
pliance sampling  in the mines  has been  on "respirable" dust sam-
pling, with, most samples collected  with a sampler  including a
10-mm nylon cyclone.

Cyclone Samplers with Other  Cut  Sizes

     The ambient atmospheric  aerosol has  two major mass modes.
The so-called "accumulation  mode" contains  some primary submicron
combustion-related particles,  (from stationary  and mobile sources),
and also the secondary  particles which  are  formed  in the  atmos-
phere from gaseous precursors by gas phase  chemical  and photo-
chemical reactions.   The mass median diameter of this mode  is
generally between 0.3 and  0.5 ym, and  little of the  mass  is  in
particles smaller than  1.0 ym or larger than 2  to  3  ym.   The
larger particles  found  in  the ambient  air,  which form the so-
called coarse mode, are generally released  by mechanical  pro-
cesses, and differ substantially in chemical characteristics
and physical properties from the accumulation mode particles.
A variety of samplers designed to aerodynamically  sort the
ambient particles into  the two major mass modes have used cyclones
to collect the  larger particles.  There is  no general agreement
on the appropriate cut  size  for  this application,  or whether
the cut-off characteristic should be sharp  or broad.  Some  prefer
                                33

-------
a sharp cut at an aerodynamic diameter of 2, 2.5, or  3.5 ym.
Others prefer a 3.5 ym aerodynamic mass median with the ACGIH
respirable cut characteristic.  Their rationale  is that there
will be little practical difference in the  size  of the two  mass
fractions for most atmospheric aerosols, and, therefore, little
justification for introducing a different sampler acceptance
standard.

     A cyclone with a sharp cut-off characteristic and intended
for two-stage ambient air sampling has been described by John,
et al.1*  The EPA has used some of the cyclone samplers developed
for "respirable" dust sampling for two-stage ambient  air sam-
pling, primarily the 1/2-in.  HASL cyclone described by Lippmann
and Harris.1*

     Several  instrument vendors market cyclone preseparators
for either source-test cascade impactors or high volume sam-
plers.  While there are no data on their performance  in the litera-
ture, calibration data on the Sierra Model  220CP cyclone have
been made available to us by  Dr. John Olin  of Sierra  Instruments,
and they have been utilized in our analyses.

     Virtual  dichotomous samplers have been widely used in  recent
years for two-stage sampling.  The precise  balance of the  two
different parallel flow streams in such samplers makes them much
more expensive  than cyclones.  On the other hand, they put  both
mass fractions  on  filters, and this is often advantageous  in
terms of subsequent analyses  of the large particle fractions.

Size-Mass Distribution Determinations

     Size-mass  distribution analyses of aerosol  constituents
have been made  using cascade  impactor samplers for more than
 thirty  years, beginning with  the original May impactor,15  and
 the Laskin16  University of Rochester modification.  They have
also been performed with aerosol centrifuges which deposit  par-
 ticles  on a  collection foil according to  their aerodynamic  size.
However, both types of sample collectors  have significant  limita-
 tions when  used for such applications.  Solid particles tend
 to  bounce off or be re-entrained from impaction  surfaces which
 lack an  adhesive layer, or whose adhesive becomes saturated.
Unfortunately,  saturation usually  is reached either before  the
 investigator  is aware of it,  or before  the  accumulated sample
 is  large enough for the subsequent analysis.  Applications  of
centrifuges  are limited by their low sampling rates and large
physical size and  cost.

     The limitations of the other  inertial  classifiers for  com-
positional  analysis by particle-size fraction have led to  the
development  of  samplers using cyclones  in either parallel  or
series  arrays.   The first development of  a  portable sampler using
a parallel  array of cyclone-filter series samplers was described


                                34

-------
by Lippmann and Kydonieus.7  Each  cyclone  had  a  different  cut
size and the overall  size-mass  distribution  of the  total aerosol,
or of any of its chemical  constitutents, could be determined
from analyses of the  collection on the  filter  following each
cyclone and a parallel  filter sampler operated without a cyclone
precollector.  The performance  characteristics of an  improved
version of this sampler  were described  by  Blachman  and Lippmann.9
Individual cyclones could  be operated at flow  rates of a, 1 to
22.5 fc/min, giving cut  points ranging from ^ 6 ym to  0.25  ym.
A much larger version of this sampler for  fixed-station ambient
air pollution sampling  was described by Bernstein,  et al.,17
having cut points at  3.5,  2.5,  1.5 and  0.5 ym.  A parallel multi-
cyclone sampling train  for stack sampling  applications was de-
scribed by Chang,18 but sufficient calibration data were not
provided to characterize the cyclone's  performance.

     A series array of  cyclones for in-stack sampling through
an eight-inch port was  described by Rusanov19  in 1969.  A  more
compact series sampler  which fit within a  six-inch  port and
sampled at 1 ft3/min  was described by Smith, et  al.20 in 1975.
It consisted of three cyclones  and a back-up filter.  The  first
cyclone, with a reported cut point of 2.6  ym,  was the T2A  cyclone
used by Chang18 in his  parallel array.  The  other two cyclones,
with nominal cut points of 1 ym and 0.5 ym,  were designed  and
constructed by Southern Research Institute (SRI)  for  this  sampler.
A later development from SRI21  is a six-stage  in-stack series
sampler which operates  at 1 ft3/min and fits through  a 10-cm
sampling port.  The five cyclones were  reported  to  have cut points
at aerodynamic diameters of 5.4, 2.1, 1.4, 0.65, and  0.32  ym.
The collection characteristics  of the cyclones in this train
are notable in that their  cut off characteristics are quite sharp,
as shown in Figure 2.  For the  SRI II cyclone, with a cut  size
of 2.1 ym, the ratio  of the particle sizes with  90% and 10% re-
moval, respectively,  is 1.5.  By comparison, for the  Andersen
Stage 4 impactor, with  a cut size of ^  2.3 ym, the  corresponding
ratio is also 1.5  (Figure 3).

     Data processing  to determine the particle size distribution
for these multi-stage samplers  can be  treated  in a  similar manner
as the cascade impactor.22  An  alternate  approach is  the  itera-
tion scheme that has  been developed by  Sinclair  and Knutson based
on the approach of Twomey.23   It will be  presented  later  in this
symposium.

AERODYNAMIC FLOW AND  PARTICLE COLLECTION  IN CYCLONES

Air Cleaning Cyclones

     The conventional view of  flow within a cyclone shown  in
Figure 1 appears to be  realistic for air  cleaning cyclones.
There is a double vortex,  with  the air  stream spiralling  downward
near the outer wall and then  upward in  a  tighter spiral  and out


                                 35

-------
  o
  LU
  o
  HI
  Z
  O

  u
  UJ
  _l
  o
  o
     100
      80
      60
40
      20
               CYCLONE I
               CYCLONE II
               CYCLONE III
               CYCLONE IV
               CYCLONE V
       0
       0.1
                                • I
                          1.0
10
                         PARTICLE DIAMETER,/zm
        Figure 2. Collection efficiencies of Southern Research Institute cyclones
               for a sampling rate of 28.3 S./min, a temperature of 25°C, and
               a particle density of 1.0 g/crr>3 (from Smith and Wilson21).

through the axial exit tube.   The particles  may  initially deposit
on the wall in  a  well-defined spiral pattern.  With continued
operation, a  dust layer will form and migrate  along the wall
to a collection hopper in a still-air zone at  the bottom of the
conical section.   The concentration of particles in an air clean-
ing cyclone is  usually quite high, which  favors  particle coagula-
tion while they are still airborne.   Since collection probability
increases with  increasing particle size,  the collection effi-
ciency increases  with increasing particle concentration.

     Tangential inlet cyclones used in air cleaning are generally
at least six  inches in diameter, have inlet  velocities of 2500
ft/min or greater,  and Reynolds numbers  in the inlets of about
100,000 or more.   Thus, the flow will be  highly  turbulent.  Par-
ticles of about 5 ym and larger can be collected with relatively
low energy consumption.  However, the energy input required to
capture smaller particles increases rapidly  with decreasing size
and is rarely worthwhile economically, except when using plenum
housings containing large numbers of  small diameter cyclones
operating in  parallel.  Particles as  small as 2  ym can be col-
lected efficiently with cyclones of 2-inch diameter when operated
with a flow rate  of about 900 A/min through  each cyclone.
                                 36

-------
      	UNCMTED STAM.CSS STEEl
        PlATCS-SoM hflKIn
      	W.»SS FIDE* FILTER
                      1.0         2.0    3.0

                        AERODYNAMIC DIAMETER,
            10.0
15.0
/am
        Figure 3. Collection efficiencies for Andersen cascade impactor stages
               at a sampling rate of 28.3 %/min {from Marple and Willeke22).


Air Sampling Cyclones

      Inertial separation efficiency in cyclones increases with
decreasing body diameter because  of the tighter turns of the
air path  and the greater relative radial acceleration of the
airborne  particles.  As a  result, the same collection efficiency
can be  achieved with lower  air  velocities.  With lower  air  veloci-
ties, the flow regime will  change from highly turbulent to  par-
tially  turbulent.  The flow is  predominantly laminar  in the small
cyclones  used in personal  "respirable" dust samplers.   However,
when  these same cyclones are used at higher sampling  rates  in
multi-stage particle size  samplers, a flow transition occurs
and the flow patterns are  affected by turbulence.  The  change
in the  nature of the flow  pattern within the cyclones with  chang-
ing flow  rate makes it difficult  to develop a general description
or predictive relationship for  cyclone performance, and makes
extrapolation from one operating  condition to another somewhat
questionable.

     Direct evidence for a  change in airflow pattern with a change
in flow rate is provided by the abrupt changes in the pressure-
flow relations.   Figure 4  shows pressure-flow data of Hochstrasser21*
for three  different 19-mm diameter long-cone cyclones.  As  the
                                 37

-------
            I
            CO
            O>
            k

            a
            n
 3



2.5



 2
            •5  1.5
            •2.

            O

            o


            u

            CO
            C/9
            O
            cc
            a.
            O
            cc,
            a

            HI
            cc


            I
            uu
            oc
            a.
1.0

 .9

 .8


 .7
 .5
 .4
 .3



.25
                .2
               .15
                .1
                                            1   I  I  I
                                CYCLONE NO. 7
            TF.CYCLONE

              NO. 4  ~


             TF

              CYCLONE

              NO. 1
                                      STABLE FLOW

                                   	UNSTABLE FLOW
                TF - LINE FOR TURBULENT

                    OUTLET PIPE FLOW

                LF - LINE FOR LAMINAR

                    OUTLET PIPE FLOW
                        I
             I
J	I
I
I  I  I  I
                 1     1.5   2  2.5  3   4  5  6 7  8 9 10


                   Q - FLOW THROUGH CYCLONE, m3/sec x 10'4




       Figure 4. Pressure-flow relationships for three 19-mm diameter long-cone

               cyclones (from Hochstrasser24),





flow  increases, a point is  reached where  there is  an  abrupt  re-

duction  in pressure  drop.   With increasing flow  thereafter,  the

pressure drop  increases again,  but the  slope of  the curve  is

lower.   The  same  phenomenon was observed  by  Blachman  and Lippmann

for the  widely  used  10-mm nylon cyclone of Dorr-Oliver.



      Blachman  and Lippmann9 presented indirect evidence for  a

change  in flow  pattern within the cyclone in terms of an abrupt

change  in the  collection efficiency characteristic at a critical
                                  38

-------
flow rate.   Figure 5 shows  that  there is an abrupt change  in
the collection characteristic  between 5.0 and 5.8  jj/min.   They
further  reported that locations  at which the particles were de-
posited  within the cyclone  change for the different  flow regimes.

     Since  the iron oxide  in  their test aerosol was  reddish in
color,  it was possible  to  observe the pattern of particle  collec-
tion along  the walls of  the white nylon cyclones.  For flows
below  5  &/min, the collection  was essentially all close to the
cyclone  inlet, with no  visible collection in the lower part of
the cyclone body.  For  higher  flow rates and small particles,
the inlet deposit extended into a spiral along the tapered inner
wall.   In addition, there  was  another separate "ring" deposit
in the lower part of the cyclone.  At a higher sampling rate,
the location of the ring deposit was lower.  Since the lower
portion of  the cyclone  is  tapered, the particles forming the
ring were depositing in a  region with a smaller diameter,  and
this presents a complication  in attempts to fit the  data into
generalized models.  The number of turns that particles traversed
before the  cyclone's collection was completed was dependent on
the flow rate and varied from 1 at 0.9 Vmin to 5 at 9.2  H/min,
For higher  flow rates,  it  was not possible to visualize the num-
bers of turns.
    10
  Q
  <
  E

   «.
  HI
  N
    1.0
  o
  UJ
    0.1
              SIERRA 220 CP
                   NH AEROTEC 3/4
                  AEROTEC 2
                                           V
                                                         \-BK-152
                                                   -BK-76
                      UNI CO 240
                             10mm DORRCLONE

                             i  i i i i 11	i  t  i  i i i i 11
      1.0
10
   100


FLOW RATE, 8pm
1,000
                                                             10,000
         Figure 5. Particle cut size, i.e., aerodynamic particle size for 50% cyclone
                retention, as a function of flow rate through cyclone for eleven
                small cyclones.
                                  39

-------
     Ring deposits  in small cyclones have  also  been  observed
by others21*'25 and  have been associated with  a  uniform radial
motion of the airstream.  Hochstrasser21* found  ring  deposits
only when there was a flow rate  below  the  critical pressure  drop
transition point.   He then inserted a  pressure  probe into the
lower cone portions of his cyclones and demonstrated that there
was a stagnant air  zone present  when flow  conditions produced
ring deposits, but  not when conventional vortex flow existed.
The height of the stagnant zone  appeared to be  proportional  to
the height of the ring deposit.   Hochstrasser associates  the
ring deposit mode of cyclone operation with a laminar flow con-
dition  in the outlet pipe of the cyclone,  as  illustrated  in  Fig-
ure 6.


     Since the  flow pattern  in  the outlet  pipe  appears to criti-
cally affect  the  performance of  the cyclone,  Hochstrasser sug-
gests that restrictions  in the  outlet  flow imposed by couplings
to  the  downstream filter or other second stage  collector  may
alter the removal characteristics of  the cyclone itself,  and
that lack of  standardization of  such couplings  may account for
some of the  reported discrepancies of  small cyclone  sampler  cali-
bration and  field performance.

     Hochstrasser noted  that  the laminar outlet pipe flow con-
dition  could  only be produced  in long-cone cyclones, i.e., having
a cone  length of  5  cm  in relation to  his cyclone diameter of
1.9 cm.  When  the cone  lengths  were changed to  2.7 or 1.6 cm,
only the turbulent  flow  condition was  observed.

     John, et al.11* confirmed  that abrupt  flow  pattern changes
cannot  be produced  in  short-cone cyclones. Their cyclone has
a body  diameter  of  3.7  cm  and  a cone  length of  4.6 cm.  There
was a vortex  in the outlet pipe under  all  test  conditions.

     John, et al. also  studied  the patterns of  deposition and
retention of  both liquid  and  solid particles  within  the cyclone.
They noted  the  following  features:

      1.  An  impaction  spot on  the wall of  the cyclone body op-
posite  the  inlet, but  slightly  off a  direct line.

      2.  A  spiral trace  of  1.25 to 1.5 turns.

      3.  A diffuse deposit on  the cone walls  increasing in den-
 sity  toward  the bottom.

      4.  Large  aggregates  of particles in  the collection cup
at  the  bottom.

      5.  A  spiral trace  in  the  outlet tube.
                                40

-------
                                                    LINE OF FLOW
                                            LAMINAR OUTLET FLOW
                                      ZONE OF STAGNATION
                      NEW THEORETICAL CYCLONE
                      LAMINAR FLOW PATTERN
       PLANE OF TRANSITION
                                            PARTICLE DEPOSITION
                                            PATTERN
                                     ZONE OF STAGNATION
                   PARTICLE DEPOSITION PATTERN
                   ( LAMINAR FLOW CYCLONE )
Figure 6. Flow pattern and particle deposition in long-cone cyclones
         operating in laminar outlet pipe flow condition (from Hochstrasser24).
                                41

-------
     6.  No measurable differences in the percentage of  the  aero-
sol penetrating to the back-up filter between liquid and  solid
particles of the same aerodynamic size.

     They also tested the cyclone for re-entrainment losses.
It was loaded with the equivalent of several days of expected
collection and then clean air was drawn  through.  The material
transferred from the cyclone walls to the outlet filter  was  about
1% per day or less.


     The  insensitivity to sample  loading and the nature  of  the
sampled material gives the  cyclone significant  advantages over
the  impactor for long-period sampling.   Figure  3 shows  that  un-
coated impaction plates  do  not retain solid particles effi-
ciently,  and that the use of filters as  impaction surfaces may
result in even greater losses.  Cyclones do not suffer  from  such
limitations and, as  shown in Figure  2,  the collection charac-
teristics can be as  sharp as those of  impactors.

      In multi-stage  samplers used for  size-mass distribution
analyses, it is desirable to have the  sharpest  possible  cut-off
characteristics for  each stage.   The work of Mercer26 and Marple
and  Willeke22 has  led  to considerable  refinement in the  design
of jet impactors and characterization  of their  performance.
While  comparable definitive work  has yet to be  performed on
cyclones, recent work, such as  that  illustrated in  Figure 2,
has  shown that  it  is possible  to  achieve relatively sharp cut-
off  characteristics  in properly designed cyclones.   The  sharpness
of the cut-off  can  be  compared  for cyclones of  different sizes
by plotting cyclone  retention  as  a function of  a normalized
particle  diameter  (Dp-D50)/D50, where  Dp is the aerodynamic
diameter  of  the test aerosol and  D50  is the diameter  at  which
the  cyclone  retention  is 50%.   Figure  7 shows  calibration data
for  5  Stairmand-type cyclones  which  have been  developed  and  cali-
brated in recent years.   The sharpest  cuts are  produced  by  the
SRI-V cyclone of Smith and  Wilson.21

      The  particle  collection characteristics of the conductive
airways of the  respiratory  tract  are  not sharp. Hence,  it  is
desirable that  pre-collectors  used for  "respirable" dust sam-
pling  should have  similar collection  characteristics.   In this
sense, the 10-mm nylon cyclone, which  is widely used for this
purpose,  is  less  than  ideal in that  it has a relatively  sharp
cut-off characteristic.   For cyclones  designed  specifically for
"respirable" dust  sampling, such  as  the 1/2-inch and 1-inch
diameter  dual-inlet  stainless  steel  cyclones developed  by the
Health and Safety  Laboratory of  the  U.S. Atomic Energy  Commis-
sion,  the potentially  sharp performance characteristics  of  cy-
clones were deliberately degraded in order to produce samplers
with appropriately coarse cut-off characteristics. "*
                                42

-------
    z
    o
    I-
      1.0
      0.8-	
      0.6
    h-
    LU
    cc
    111
    O 0.4
      0.2
                                                   I
       -1.0
 -0.5             0             0.5

NORMALIZED PARTICLE DIAMETER, Dp-D5o/D5o
1.0
         Figure 7. Cyclone retention as a function of normalized particle diameter
                for five small cyclones which have recently been calibrated.
                Dp is the aerodynamic particle size of the test aerosol and
                is the aerodynamic size for 50% cyclone retention.
      The variation  of experimentally  determined particle cut
 sizes with sampling rate is illustrated in Figure 5  for  a variety
 of  sampling cyclones.  For each cyclone,  there are characteristic
 relations between cut size and sampling rate-  Most  of  the cali-
 bration data are  for aerodynamic particle sizes between  1 and
 10  vim.  Some of the cyclones, specifically the 10-mm Dorr-Oliver
 and the SRI-V, have calibrations for  cut  sizes extending to 0.5
 Mm  and below.  Furthermore, as shown  in Figure 7, the SRI-V has
 a relatively sharp  cut-off characteristic for such small par-
 ticles.  Thus, it is particularly  well suited for use as the
 final inertial stage in a multi-stage size-mass sampling instru-
 ment.
PREDICTIVE RELATIONS

     Chan  and Lippmann27  showed that previously proposed predic-
tive relations for cyclone  efficiency  (Rosin,  et al.,ZB Lapple,29
Leith  and  Licht,31 and  Beeckmans32) are  inconsistent with  experi-
mental observations in  tests using low concentrations of mono-
disperse test aerosols.   Using a hyperbolic  tangent relation
                                 43

-------
for cyclone performance  first  developed  by  Blachman  and  Lipp-
mann,9 they also described  the empirical constants of  this equa-
tion for four commercially  available  small  cyclones  which  have
been used in air sampling and  for  several Stairmand-type cyclones,
It should be noted  that  the previous  predictive  theories were
developed from  test data on, and have primarily  been applied
to, cyclones used for  air cleaning applications.

     Hochstrasser21* and  John,  et al.11* also attempted  to adapt
available predictive relations to  their  experimental data.  Fig-
ure 8  shows the comparison  of  Hochstrasser's experimental  data
with the predicted  values for  one  of  the cyclones he tested.
He concluded that for  operational  conditions where  there was
turbulent flow  in the  outlet pipe, either the Earth  equation
or the hyperbolic tangent formulation provided consistently good
predictions.  On the other  hand, for  operational conditions where
the flow in the outlet pipe was laminar, only the Blachman and
Lippmann formulation was consistently reliable.   Both  the  Leith
and Licht and the Lapple equations were  unreliable  for all cases.

     John,  et al.11* compared their data  to  predictions based
on  the theoretical  formulations of Lapple,2  Sproull,33  Leith
and Licht,31 and Barth.30   They found that  none  of  them fit the
data,  although  the  predicted slope of the efficiency curve from
the Barth  relation  was closer  to that observed than  were any
of  the others.   They did not attempt  to  fit their data to  the
hyperbolic  tangent  relation of Blachman  and Lippmann.9

      The discrepancies between the conventional  predictive theo-
ries  and experimental  performance  could  be  due to any  or all
of  the following  differences between  the conditions  within cy-
clones used in  air  cleaning as opposed to cyclones  used in air
sampling:  (1)  in  air cleaning, the concentrations are  much higher
 than  the  ambient  aerosols;  (2) in  air sampling cyclones, the
particles  usually  remain on the wall  where  they  were initially
deposited,  while  in air  cleaning cyclones,  deposited particles
are continually scoured  from the initial deposition  sites  and
migrate to the  collecting  hopper;  (3) the flow patterns in air
 cleaning  cyclones  are  always turbulent,  while in the smaller
 cyclones  used  in air  sampling, the flows may be  completely or
partially  laminar.


      The various cyclone theories  are summarized in  Table  1.
The complete expression  for the hyperbolic  tangent  equation as
developed  by Chan  and  Lippmann27  is:


      n = 0.5 +  0.5  tanh
+ (A - 2B)—?  + B _ A
                                           KQn
                                44

-------
       100
    6?
     *

    O

    UJ
    U
    UL
    U.
    UJ

    O
    111
    O
    O
    UJ

    s
    U
    U
       30 —
       20
        10
                           LEITH & LIGHT
                           L APPLE
                           BARTH
                           LIPPMANN & BLACHMAN
                           DATA ( TURBULENT O.P. FLOW
                           DATA ( LAMINAR O.P. FLOW )
                 12345

                  dp (MMAD) - PARTICLE DIAMETER,,
Figure 8. Experimental cyclone collection data of Hochstrasser in comparison
         with predictions based on various predictive relations (from
         Hochstrasser24).
                                  45

-------
     The constants K and n are obtained  from a plot of  the  ex-
perimentally determined particle cut sizes at several sampling
rates.  The constants A and B are determined using a least-squares
fitting program for all of the pertinent  experimental efficiency
data.

     A summary of the four empirical constants and the  ranges
of particle size and flow rate over which they apply is presented
in Table 2 for eleven small cyclones for  which a  sufficient cali-
bration data base exists.

SUMMARY

     Cyclones have many advantages over  other inertial-type par-
ticle separators for the in-situ classification of sampled  aero-
sols.  They are much smaller, more easily portable, and less
dependent on orientation than elutriators or centrifuges; they
are much less subject to errors by misclassification due to par-
ticle bounce or overloading of collection surfaces than conven-
tional jet impactors; and they are much  simpler than virtual
dichotomous samplers.  On the other hand, the performance char-
acteristics of properly designed and operated elutriators,  cen-
trifuges, jet impactors, and dichotomous  samplers are predictable
from  first principles, while the prediction of cyclone  perform-
ance  is dependent on empirical calibration data.  Therefore,
better predictive relations for cyclone  collection efficiency
are needed in order to exploit the inherent advantages  of cy-
clones for air sampling.  A generalized  predictive empirical
relationship  for cyclone performance has  been developed and
described.   It has  been applied to the available  calibration
data  for  the  eleven small cyclones for which reliable calibra-
tions exist,  and the four characteristic  constants have been
determined for each.  The equation permits the calculation  of
cyclone collection  efficiency for any aerodynamic particle  size
and  flow  rate within the range established by the original
calibration.

      The  cyclones evaluated vary considerably in  their  sharpness
of cut.   Some have  coarse cut-off characteristics which match
those of  the  ACGIH  cut-off for "respirable" dust.  Others have
much  sharper  cut-off curves, comparable  to those  of jet impactors,
and  are,  therefore, useful for multi-stage samplers for determin-
ing  size-mass distributions.
                                46

-------
                        TABLE 1.   SUMMARY OF CYCLONE COLLECTION THEORIES

Category
I. Conventional
II. Semi-empirical
III. Theoretical
Theory
Rosin (1932)
Lapple (1951)
Davies (1952)
Barth (1956)
Sproull (1970)
Leith and Licht (1972)
Beeckmans (1973)
Soo (1973)
Form of Equation
•>.. • ^°-5
T, - 1 - e£(D'Q)
n = 1 - (infinite series with
algebraic and exponential
terms)
Reference
28
29
34
30
33
31
32
35
IV.  Empirical
Wagner and Murphy  (1971)
Lippman and Chan  (1974)
Chan and Lippmann  (1977)
Beeckmans and Kim  (1978)
D    — b-n u
 5 Q •— r*\£
n = FJTanh[f (D,D50)]}
n = F|Tanh[f(Q,D' '
n = F (St,Re)
36
12
27
37

-------
                 TABLE  2.   EMPIRICAL CONSTANTS  FOR CYCLONE EFFICIENCY CALCULATIONS
oo

Cyclone
Aerotec 2
UNICO 240
Aerotec 3/4
10-mm nylon


BK-152
BK-76
19-mm UC-1
AIHL
Sierra 220 CP
SRI IV
SRI V
D / ym, AED
2.5-4.0
1.0-5.0
1.0-5.0
1.8-7.0
1.0-1.8
0.1-1.0
2.0-5.0
1.0-3.0
2.0-5.0
2.0-7.0
1.0-10.0
0.5-3.0
0.3-2.0
Q, Jl/min
350-500
65-350
22-65
0.9-5.0
5.8-9.2
18.5-29.6
1150-2700
400-1100
6-25
8-27
7-85
7-28
7-28
K
468.01
123.68
214.17
6.17
16.10
178.52
4591.0
221.48
15.46
52.48
48.08
17.60
14.00
n
-0.80
-0.83
-1.29
-0.75
-1.25
-2.13
-0.98
-0.77
-0.636
-0.99
-0.86
-0.98
-1.11
A
2.02
1.76
2.04
3.07
1.19
0.74
0.914
0.507
2.927
2.906
2.163
1.580
4.928
B
-0.68
-0.82
-0.77
-0.93
-0.59
-0.07
-0.111
-0.026
-0.849
-0.547
-0.370
-0.202
3.347
Reference
12


4


37

24
14
—
21


-------
ACKNOWLEDGEMENT

     This study was part of a center program  supported  by  Grant
No. ES-00260 from the National  Institute  of Environmental  Health
Sciences.

REFERENCES

 1.  AIHA Aerosol Technology Committee.   Guide  for  Respirable
     Mass Sampling.  J. Am. Ind.  Hyg.  Assoc.  31:133-137, 1970.

 2.  Lippmann, M.   "Respirable" Dust Sampling.   J.  Am.  Ind.  Hyg.
     Assoc.  31:138-159, 1970.

 3.  Lippmann, M.   Size-Selective Sampling for  Inhalation  Hazard
     Evaluations.   In:  Fine Particles, B.Y.H.  Liu,  ed. Academic
     Press,  New York, 1976.  pp.  287-310.

 4.  Lippmann, M.,  and W.B. Harris.  Size-Selective Samplers
     for Estimating  "Respirable"  Dust  Concentrations.   Health
     Phys.  8:155-163, 1962.

 5.  Kotrappa, P.   Revision of  Lippmann-Harris  Calibration for
     Two-Stage Sampler Using Shape Factor.  Health  Phys. 20:350-
     351, 1971.

 6.  Ettinger, H.J., J.E.  Partridge, and  G.W. Royer.  Calibration
     of  Two-Stage Air Samplers.   J. Am. Ind.  Hyg. Assoc. 31:537-
     545, 1970.

 7.  Lippmann, M.,  and A.  Kydonieus.   A Multi-Stage Aerosol  Samp-
     ler for Extended Sampling  Intervals.  J. Am. Ind.  Hyg.  Assoc
     31:730-738,  1970.

 8.  Seltzer, D.F.,  W- Bernaski,  and J.R.  Lynch.  Evaluation
     of  Size-Selective Presamplers.  II.   Efficiency of the  10-
     mm  Nylon Cyclone.  J. Am.  Ind. Hyg.  Assoc.  32:441-446,  1971.

 9.  Blachman, M.W., and M. Lippmann.  Performance  Characteris-
     tics of the Multi-Cyclone  Aerosol Sampler.   J. Am.  Ind.
     Hyg. Assoc.  35:311-316, 1974.

10.  Caplan, K.J.,  L.J. Doemeny,  and S.D.  Sorenson.  Performance
     Characteristics of the 10-mm Cyclone Respirable Mass  Sampler.
     Part I. Monodisperse Studies.  J. Am.  Ind.  Hyg. Assoc.
     38:83-95, 1977.

11.  Tomb,  T.F., and L.D.  Raymond. Evaluation  of Collecting
     Characteristic of Horizontal Elutriator  and 10-mm  Nylon
     Cyclone Gravimetric Dust Samplers.   Presented  at 1969 Annual
     Meeting, American Industrial Hygiene Association,  Denver,
     May, 1969.
                               49

-------
12.  Lippmann, M., and T.L. Chan.  Calibration of Dual-Inlet
     Cyclones for "Respirable" Mass Sampling.  J. Am.  Ind.  Hyg.
     Assoc. 35:189-200, 1974.

13.  Threshold Limits Committee.  Threshold Limit Values  of Air-
     borne Contaminants for 1968.  American Conference of Govern-
     mental Industrial Hygienists, Cincinnati, 1968.

14.  John, W., G.P. Reisehl, and J.J. Wesolowski.  Final  Report,
     California Air Resources Board Contract No. A5-00487,  Feb-
     ruary 1978.

15.  May, K.R.  The Cascade Impactor, an  Instrument  for Sampling
     Coarse Aerosols.  J. Sci. Instrum. 22:187-195,  1945.

16.  Laskin, S.  The Modified Cascade Impactor.  UR-129,  Univer-
     sity of Rochester Atomic Energy Project, Rochester,  NY,
     August, 1950.

17.  Bernstein, D., M.T. Kleinman, T.J. Kneip, T.L.  Chan, and
     M. Lippmann.  Development of a High-Volume Sampler for the
     Determination of Particle Size Distribution in  Ambient Air.
     J. Air Pollut. Control Assoc. 26:1069-1072, 1976.

18.  Chang, H.C.  A Parallel Multicyclone Size-Selective  Partic-
     ulate Sampling Train.  J. Am. Ind. Hyg. Assoc.  35:538-545,
     1974.

19.  Rusanov, A.A.  Determination of the  Basic Properties of
     Dust and Gases.  In:  Ochistka Dymovykh Gasov v Promysh-
     lennoy Energetike, A.A. Rusanov, I.I. Urbakh, and A.P.
     Anastasiadi, eds. "Energiya".  Moscow, 1969.

20.  Smith, W.B., K.M. Gushing, G.E. Lacey, and J.D. McCain.
     Particulate Sizing Techniques for Control Device  Evalua-
     tion.  EPA-650/2-74-102a, U.S. Environmental Protection
     Agency, Research Triangle Park, NC,  1975.  132  pp.

21.  Smith, W.B., and R.R. Wilson.  Development and  Laboratory
     Evaluation of a Five-Stage Cyclone System.  EPA-600/7-78-
     008, U.S. Environmental Protection Agency, Research  Triangle
     Park, NC, 1978.  66 pp.

22.  Marple, V.A., and K. Willeke.  Inertial Impactors:   Theory,
     Design and Use.  In:  Fine Particles, B.Y.H. Liu,  ed.  Academ-
     ic Press, New York, 1976.  pp. 411-446.

23.  Twomey, S.  Comparison of Constrained Linear Inversion and
     an Iterative Nonlinear Algorithm Applied to the Indirect
     Estimation of Particle Size Distributions.  J.  Coniput. Phvs
     18:188-200, 1975.
                                50

-------
24.  Hochstrasser, J.M.  The Investigation and Development of
     Cyclone Dust Collector Theories for Application  to Miniature
     Cyclone Presamplers.  Ph.D. Thesis, Department of Environ-
     mental Health, College of Medicine, Univ. of Cincinnati,
     1976.

25.  LOffler, F.  The Calculation of Centrifugal Separators.
     Staub Reinhalt. Luft  (in English) 30:1-5, Dec. 1970.

26.  Mercer, T.T.  Aerosol Technology in Hazard Evaluation.
     Academic Press, New York, 1973.  pp. 297-304.

27.  Chan, T.L., and M. Lippmann.  Particle Collection Efficien-
     cies of Air Sampling Cyclones:  an Empirical Theory.  Environ.
     Sci. Technol. 11:377-382, 1977.

28.  Rosin, P., E. Rammler, and W. Intelman.  Principles and
     Limits of Cyclone Dust Removal.  Z. Ver. Deut. Ing. 76:433-
     437, 1932.

29.  Lapple, C.E.  Dust and Mist Collection.  In:  Chemical En-
     gineers' Handbook, J.K. Perry, ed. McGraw-Hill,  New York,
     1963.

30.  Earth, W.  Calculation and Design of Cyclones on the Basis
     of Recent Tests.  Brennst. Waerme Kraft 8:1-9, 1956.

31.  Leith, D., and W. Licht.  The Collection Efficiency of Cy-
     clone Type Particle Collectors—A New Theoretical Approach.
     AIChE Symp. Ser. No. 126, 68:196-206, 1972.

32.  Beeckmans, J.M.  A Two-Dimensional Turbulent Diffusion Model
     of the Reverse Flow Cyclone.  J. Aerosol Sci. 4:329-336,
     1973.

33.  Sproull, W.T.  Air Pollution and Its Control. Exposition
     Press. NY, 1970.

34.  Davies, C.N.  The Separation of Airborne Dust and Parti-
     cles.  Proc. Inst. Mech. Eng. London B (1):185-198, 1952.

35.  Soo, S.L.  Particle-Gas Surface Interactions in  Collection
     Devices.  Int. J. Multiphase Flow 1:89-101, 1973.

36.  Wagner, J., and R.S. Murphy.  Miniature Liquid Cyclones—Effects
     of Fluid Properties on Performance.  Ind. Eng. Chem. Process
     Des. Dev. 10:346-352, 1971.

37.  Beeckmans, J.M., and C.J. Kim.  Analysis of the  Efficiency
     of Reverse Flow Cyclones.  Can. J. Chem. Eng., in press.
                                51

-------
                              PAPER  3
            RESEARCH ON DUST  SAMPLING  AND MEASUREMENT
                        IN OUR  LABORATORY
                           KOICHI  IINOYA
                DEPARTMENT OF CHEMICAL ENGINEERING
                         KYOTO UNIVERSITY
ABSTRACT

     The presentation includes four topics of particle sampling
and measurement studied in our laboratory during the last  few
years.

     1.  Anisokinetic sampling errors by round and slit probes
         for wide ranges of Reynolds number and inertia parameter.

     2.  Sampling efficiency for particles by a ribbon which
         has various inclination angles to the flow direction
         for wide ranges of Reynolds number.

     3.  Fractional efficiency of impactor, taking into account
         velocity distributions in the boundary layer at nozzle
         outlet.

     4.  Effect of probe diameter on isokinetic sampling error
         in experiments.

     Details of the four research topics are given in the  fol-
lowing  sections.

ANISOKINETIC SAMPLING ERRORS OF PARTICLE CONCENTRATION BY  ROUND
AND SLIT PROBES

     In order  to examine the errors in measuring particle  concen-
tration due to anisokinetic sampling over a wide range of  inertia
parameters, theoretical and experimental studies have been con-
ducted.1'2  In the experiments, a monodisperse methylene blue-
uranine aerosol generated  by a spinning disc and lycopodium


                                52

-------
spores were  sampled by  a round and  a slit type probe respectively
as  shown  in  Figures 1 and 2.   Figure 3  shows  the  details of  these
two kinds of  test  probes.  The experimental conditions  are given
in  Table  1.
      1. SPINNING DISK AEROSOL GENERATOR
      2. CORONA IONIZER
      3. MIXING CHAMBER
      4. BAUSCH AND LOMB PARTICLE COUNTER  8. SAMPLING PROBE
      5. ORIFICE METER                     9. VACUUM PUMP
      6. FILTER                          10. WET GAS METER
      7. BLOWER                          11. FILTER BOX
           Figure 1. Schematic diagram of horizontal experimental apparatus for
                   methylene blue-uranine aerosol by spinning disc generator.
                                 '. CONSTANT FEEDER
                                 2. DISPERSER
                                 3. CORONA IONIZER
                                 4. SAMPLING PROBE
                                 5. ORIFICE
                                 6. WET GAS METER
                                 7. VACUUM PUMP
                                 8. BLOWER
                                 9. SAMPLING FILTER BOX
                                    II
           Figure 2. Schematic diagram of vertical experimental apparatus for
                   lycopodium spores.
                                      53

-------
             -as—j«-25—JOB-
           FILTER BOX
                                          •—40
                                            UI
                            Earth

                      BRASS PROBE
           ACRYLIC PROBE

SLIT PROBE         ROUND PROBE
                  Figure 3. Sampling probes and filter box.
                 TABLE 1.  EXPERIMENTAL  CONDITIONS



Particles
Lycopodium spores
Methylene blue-
uranine
Methylene blue-
uranine
Air Velocity,
u0 (m/sec)
Inertia Parameter,
P
Flow Reynolds
lumber
Geometric
Particle standard
size, deviation,
Dpso(Vm) ag
33 (24) 1.09
3,5 1.07

4.3 1.07

0.2 - 15.
0.05 - 3.

(1.1 - 81)

Particle
density,
Pp(9/cm3)
1.05
1.42

1.42

0
4

x 10 3

Concentration
in liquid
(wt %)
-
0.21

0.5





     Theoretical  results obtained under the assumption of poten-
tial flow are mostly in good agreement with experimental data
for both types  of probe, as shown in Figures 4,  5  and 6.  How-
ever, the anisokinetic sampling errors obtained  from experiments
with the slit probe  are smaller than the calculated  values in
the large inertia region (lycopodium), as shown  in Figure 7
In general,  it  is possible to use these figures  to estimate*
                                54

-------
anisokinetic  sampling errors.   It  is also recognized that the
concentration errors become smaller  as  the sampling  velocity
(u)  becomes extremely high.  Therefore,  the super high speed
sampling  may  be a practically  simple method for particulate sam-
pling without the tedious procedure  of  isokinetic sampling.
o
I-
            o
            111
            o
            1
                 	THEORETICAL
                      CURVE
                 METHYLENE BLUE
                   URANINE
            WITH CORONA
              IONIZER
                                   ROUND PROBE
                                         5m/s R=0.52cm P=0.05(-)3.47il
o u0 = 8m/s R=0.52cm P=0.12<-)4.28jU

A U(J = 6.5m/s R=0.42cm P=0.12(-)4.28M
A u0 = 15ms R=0.42cm P=0.29(-)4.28M
                             VELOCITY RATIO,— (-)
                                           u
            Figure 4. Anisokinetic sampling errors of round probe for smaller
                    particles (methylene blue-uranine particles).
                o
                O
                IU
                o
           a P = 1.80
           o p = 0.47
           • P = 0.07
         I Dp = 24 Mnr
                                 LYCOPODIUM
                                   SPORES
                         •WITH GRAVITY FORCE
                         USING SCHILLER-
                         NAUMANN EQUATION -
                         ROUND PROBE
                           VELOCITY RATIO,— (-)
           Figure 5. Anisokinetic samp/ing errors of round probe for larger
                   particles (lycopodium spores).
                                     55

-------
                                    WITH CORONA IONIZER


                                    P = 0.035


                                    P = 0.18


                                    P = 0.43
O U0 = 1 m/s Dp = 3.47 jum
                                     METHYLENE BLUE - URANINE
                                       — THEORETICAL CURVE

                                         SLIT PROBE
                           VELOCITY RATIO,-^ (-)
              Figure 6. Anisokinetic sampling errors of slit probe for smaller

                      particles (methylene blue-uranine particles).
              2.5
           O
           cc
           h-
           z
           O
           u
              1.5
              0.5
                   o P = 6.22M


                   • P = 1.24(-}


                   n P = 0.25I-)
                                    	1	r



                                    WITH CORONA IONIZER
                          LYCOPODIUM SPORES


                          	THEORETICAL


                          SLIT PROBE Dp = 24 jim
                         0.5        1        1.5



                            VELOCITY RATIO,—(-)
                                              2.5
                Figure 7. Anisokinetic sampling errors of slit probe for larger

                        particles (lycopodium spores).
      The  amounts  of particulate  deposited  in the probe  and  the

sampling  tube  are also  examined,   it  is found  that  the  deposit

shows a minimum value at Reynolds numbers  of 2000 to 3000 for
                                      56

-------
both probes, as shown in Figures'8 and  9,  and  that  the  amount
of deposit in an acrylic probe  is much  more  than  that in  a  brass
one, as shown in Figure 8.

Nomenclature

     c  : measured concentration

     c0 : mainflow concentration

     D  : particle diameter

     M  : deposited mass in  the probe and  sampling  tube

     Mf : collected mass on  the filter

     P  : inertia parameter  = p D2u0/(18iaR)  =  2¥
                               P P
     R  : probe radius

     u  : sampling velocity

     u0 : main gas velocity

     Re : Reynolds number  in sampling probe

     p  : gas density

     p  : particle density

     \i  : gas viscosity

SAMPLING EFFICIENCY FOR PARTICULATES BY RIBBON

     Average and local impaction efficiencies  for a ribbon, at
various angles of inclination to the flow  direction, have been
calculated for a wide range  of particle Reynolds  numbers  from
the Stokes to Newton regions.3  The calculations  were based on
a discontinuous potential  flow model1*"10,  which is  in good  agree-
ment with the observation of paraffin mist streamlines  around
the ribbon as shown in Figure 10.


     The experimental apparatus is shown in  Figure  11.  The cal-
culated sampling efficiencies agree well with  the experimental
results of lycopodium spores, which have a settling velocity
of 1.76 cm/sec in air, as shown in Figures 12  and 13.   The  ef-
ficiency decreases as the particle Reynolds  number  increases
for the region beyond the Stokes one.   The smaller  the  inclina-
tion angle of a ribbon, the  higher the  sampling efficiency.
This tendency is also observed beyond the  Stokes  region as  shown
in Figure 14.  Local impaction efficiencies  are higher  at the


                                57

-------
      £•102
     O
     O
     O.
     UJ
     Q
     UJ
     co
     o
     Cu
     a.
          50
          30
  .OLYCOPODIUM
     SPORES
    , METHYLENE BLUE - URANINE
     (ACRYLIC PROBE)
10


 5
 QMETHYLENE BLUE
  URANINE
\ (BRASS PROBE)
                           ROUND
                              PROBE
 102              103             104

         REYNOLDS NUMBER Re(-)
Figure 8. Relationship between deposition ratio and Reynolds
         number in round probe.
        +50 - O LYCOPODIUM
              • METHYLENE BLUE
                URANINE
                (ACRYLIC PROBE)
                           103              1Q4

                   REYNOLDS NUMBER Re(-)
  Figure 9. Relationship between deposition ratio and Reynolds
           number in slit probe.
                              58

-------
Figure  10.  Calculated streamlines superimposed on photograph
           of wake.
                  AIR
                 4U
             100
        PARTICLES
               I
   -DISPERSER

   AIR AND
   PARTICLES/

RECTANGULAR,
DUCT
      GRADUATION
      OF DEGREE
            M
                           VENTURI FLOWMETER
                          r^
                 in
                 m
                                               GATE
                                               VALVE
                         n
                     CYCLONE

                                      BLOWER
                               GLASS WINDOW
                             WINDOW
   Figure 11.   Schematic diagram of experimental apparatus.

-------
UJ
u
u.
o

§
                                                                  = 103

                                                                  = 104
                                                         THIS WORK
                                                         (CALC.)
                            THIS WORK 30<4>< 160
I 0.2I-
0.5
12         5       10

  INERTIAL SIZE PARAMETER
                                                        20
50
100
         Figure 12.   Relation between impact/on efficiency and inertia
                     parameter for a ribbon perpendicular to the flow.
                    INERTIAL SIZE PARAMETER
      Figure 13.   Relation between impaction efficiency and inertia
                  parameter for a ribbon inclined to the flow at  = 10?.
                                     60

-------
                0.2    0.5   1    2      5
                 INERTIAL SIZE PARAMETER
             (A)
                                    = 0
  0.5   1    2      5   10

INERTIAL SIZE PARAMETER

           (B)     $ = 103
                                              20
50
   0.5   1    2      5    10
INERTIAL SIZE PARAMETER
          (C)     * = 104
                                               20
 50
                                                -)
Figure  14.  Relations between impact/on efficiency and inertia parameter
           for a ribbon inclined to the flow at 0 = 0 (Stokes flow),
           103, and JO4.
                                 61

-------
leading edge  (x=l) than those at  the  trailing  edge  (x=-l)  of
an inclined ribbon.  The average  sampling  efficiencies  are de-
termined along the transverse line at a distance  of  20% of ribbon
width from the leading edge, as shown in Figure  15A.  Therefore,
the microscopic observation of sampled particles  should be con-
ducted along this line.  Experimental local  impaction efficien-
cies are generally in good agreement with  the  theoretical  results
as shown in Figures 15 A and C.   As the inclination  angle  becomes
smaller than 90 degrees, the local impaction efficiencies  are
higher at the leading edge and lower at the  trailing edge  of
the ribbon than those of 90 degrees, and the efficiencies  of
the inclined ribbons change little at the  center  line of ribbon,
compared with those of 90 degrees, as shown  in Figures  15  A,
B, C.

Nomenclature

     D     : particle diameter

     r     : half width of ribbon

     Re    : particle Reynolds number for main gas velocity
       P°    (=Dppu0/u)

     ufl    : main air velocity

     x     : distance from the center line  of ribbon

     B     :  inclination angle of  ribbon to flow direction

     n     :  impaction  (sampling)  efficiency

     n     :  local  impaction efficiency
       X

     p     :  air density

     p     :  particle density

     p     :  air viscosity

     $     :  parameter which accounts for particle motion bevonrl
             Stokes1 law = Re2 7(2^)                         *
                            po'

     Y     :  inertia parameter for Stokes'  law = D2p u /(36Mr)

FRACTIONAL EFFICIENCIES OF ROUND  AND SLIT  NOZZLE  IMPACTORS

     Separation mechanisms of an  impactor  have usually  been  stud'
by use of  a potential flow model.  However,  there is some  dis-
crepancy between such theoretical results  and the experimental
data.  In  the present study, the  theoretical impaction  efficien
cies have  been calculated, taking into account the velocity


                                62

-------
                                            	LEWIS ET AL. (CALC.)
                                            	THEORETICAL RESULTS
                                                (THIS WORK)
                                             •  EXPERIMENTAL RESULTS
                                                (THIS WORK, •v/2>JF= 0.9)
                                             X  AVERAGE EFFICIENCY
                             0    0.4   0.8 1
                         DISTANCE FROM CENTER
                         LINE OF RIBBON X(-)
                            (A)
= 90°
                                    0             1
                 -J   DISTANCE FROM CENTER LINE
                      OF RIBBON X(-)
                              (B)    0 = 10°
                                   0             1
                 3    DISTANCE FROM CENTER LINE
                      OF RIBBON X(-)
                             (C)       p = 30°

Figure 15.   Local impaction efficiencies for a ribbon of various inclined
            angles at $ = 0 (Stokes flow).
                                   63

-------
boundary layer of incompressible gas at the nozzle outlets.
The theoretical results are in good agreement with the experi-
mental values for a round11'12 and a slit nozzle impactor, respec-
tively.  Figure 16 shows the fractional efficiency of a slit
nozzle impactor as an example.


     Effect of the clearance ratio  (Rc), which  is  defined as
the ratio of  the distance between nozzle and  impaction plate
to the nozzle diameter, on  the fractional efficiency  has  been
calculated by use of a potential flow model13  for  a round nozzle
impactor, as  shown in Figure 17.llf  The calculated efficiencies
are in good agreement with  experimental results for the  ratios
of 2,  1, 0.5, 0.33 and 0.25 as shown  in Figure  18  as  an  example.
Table  2 gives the approximate straight  line equations of  these
fractional curves.

     Particle precipitating efficiencies on the inner wall of
a  slit nozzle impactor have also been theoretically calculated
by use of a velocity distribution15 in  the region  where  the
motion of a particle is mainly influenced by  gravitational and
 inertia  forces.  The nozzle and the calculated  efficiencies  are
 shown  in Figures 19  to 23.16  The experimental  results obtained
 by use of lycopodium spores and ragweed pollens are in good
 agreement with  the calculated precipitating efficiencies, as
 shown  in Figure  24.

     TABLE 2.  APPROXIMATE EQUATIONS OF FRACTIONAL EFFICIENCIES
 	FOR  VARIOUS CLEARANCE RATIOS OF  ROUND  NOZZLE IMPACTOR	

                          Approximate  equations  of  fractional
 Clearance  ratio,  R        efficiency,  nm
                  C                    J.

          5                     2.34/7  -  0.427

          3                     3.17/7 -  0.649

         1-3                   3.80/7  -  0.954   (Ranz)

          1                     4.74/7  -  1.05

         0.5                   5.63/7 -  1.26
                               64

-------
                 1



                0.9



                0.8




                0.7



                0.6




              7 0.5



              * 0.4



                0.3



                0.2



                0.1
 DC = 0.142cm
DC = 0.07 cm
POTENTIAL

FLOW

(DAVIES)


Rc>2
                  A YUU

                    Re = 0.5


                  •  RANZ

                    Rc= 1-3
                   0  0.1 0.2 0.3  0.4 0.5 0.6 0.7 0.8 0.9  1
        Figure 16.  Relation between fractional efficiency and inertia parameter

                 for a slit nozzle impactor (S.  Yuu).
Nomenclature



     C    :  Cunningham slip correction factor



     D    :  nozzle  diameter or width at outlet
      C


     G    :  gravitational parameter or dimensionless settling

            velocity  = Cp Dpg/(18yu0)



     L    :  distance  from nozzle  outlet to  impaction plate



     L    :  dimensionless nozzle  length = fc/D
                                               G


     &    :  length  of converging  part of nozzle



     R    :  clearance ratio = L/D



     Re.  :  Reynolds  number based on nozzle outlet



     u0   :  gas velocity at nozzle outlet



     a    :  half-angle of converging nozzle



     n    :  impaction (target or  fractional) efficiency
                                  65

-------
     nwc  : calculated precipitating  efficiency on the inner nozzle
           wall

     ¥    : inertia parameter = CD*p  u0/(18UD )
                                  c c        C
EFFECT OF PROBE  DIAMETER ON ISOKINETIC SAMPLING ERRORS

     In order  to examine the effect  of probe diameter on  iso-
kinetic sampling errors, experimental  studies have been conducted
using methylene  blue-uranine aerosol and lycopodium spores  in
the small and  large inertia regions  respectively.17   It is  found
that the  standard deviation of concentration ratio, defined as
the concentration measured by a probe  of any diameter divided
by that of a 1-cm diameter probe, becomes larger as the probe
diameter  decreases.  The following empirical equations are  ob-
tained  by use  of the method of least squares, assuming that the
standard  deviation is inversely proportional to the square  root
of sampling  amount W.

      a  =  9.19  x 10~3 W~°'5 d~°'31; for lycopodium              (1)

      a  =  7.25  x 10"" W~°'5 d~°-28; for methylene blue-uranine  (2)
                                Re = 0.50
                                    I
                                Rc= 1.0

                                Re = 2.0
                          0.1  0.2  0.3  0.4  0.5
        Figure 17.  Relation between fractional efficiency and inertia parameter
                for various clearance ratios of a round nozzle impactor.
                                 66

-------
                     0.9


                     0.8


                     0.7



                     0.6



                  1 0.5
                   R-

                     0.4



                     0.3



                     0.2



                     0.1
17=5.63
                       0'	
                       0.1   0.2   0.3   0.4  0.5
Figure 18.   Relation between  fractional efficiency and inertia parameter
             for clearance ratio Rc = 0.5 of a round nozzle impactor.
                                   67

-------
                   NOZZLE WALL
                  FLUID FLOW LINE
                             - CRITICAL TRAJECTORY
                             OF PARTICLE
              Figure 19. Schematic diagram of two-dimensional nozzle.


A comparison  of  experimental data with  the  results calculated
by the above  equations  is shown in Figure  25.

     It  is also  found in the small inertia  region that the mean
values of concentration ratio measured  by  smaller diameter probes
differ with each other  and significantly deviate from unity  in
some cases, as shown in Figure 26.
     c

     GO


     d

     n
:  mean measured concentration (g/m3)

:  mean measured concentration for 1-cm reference probe
  diameter  (g/m3)

:  inner probe diameter  (cm)

:  number of trial
                                 68

-------
u0  :  main flow  velocity  far upstream  of probe  (m/sec)

W   :  amount of  sample  (g)

a   :  nondimensional  standard deviation of  sample

a,  :  nondimensional  standard deviation by  reference probe
      of  1 cm  diameter
               i
              0.8
              0.6
              0.4
              0.3

              0.2
             0.08
             0.06

             0.04
             0.03
             0.02
             0.01
*
a.
L
0.36
0.2121(radianM2°
20
TAwcmaxj 0.8323
= 5
               0.001    Q.003 0.006 0.01
                              G <-)
            0.03  0.06 0.1
 Figure 20.  Calculated settling efficiencies for different Reynolds numbers,
           taking account of air velocity distribution at nozzle entrance.
                               69

-------
              0.06

              0.04
              0.03

              o.o:
                    Re;
                   Re:
Rej = 50x
*
Oi
L
ffa/cmax
0.36
0.21 21 (radian)
12°
20
0.8823
                                            I    II   II
                0.001    0.003   0.006 0.01
                                    G (-)
                            0.03   0.06 0.1
Figure 21.   Calculated settling efficiencies for different Reynolds numbers
             with uniform air velocity at nozzle  entrance.
               0.2
               0.02
               0.01
                        50
                       15
                    ~f<0.36
Rej
a
L
^cmax
200
0.21 21 (radian)
120
20
0.8823
                0.001     0.003  0.006  0.01
                                    G <-)
                            0.03  0.06 0.1
Figure 22.   Calculated settling efficiencies for various inertia parameters,
             taking account of air velocity distribution at nozzle entrance.
                                      70

-------
                  1
                0.8
                0.6
                0.4
                0.3
                0.2

             o  0.1
            flo.08
               0.06

               0.04
               0.03

               0.02
Re;
*
a
200
0.36
0.21 21 (radian)
12o
                            L = 60
               0.01
                0.001     0.003 0.006 0.01
                                     G (-)
                      0.03  0.06 0.1
Figure 23.   Calculated settling efficiencies for various nozzle lengths,
             taking account of air velocity distribution at nozzle entrance.
                  1
                0.8
                0.6
                0.4
                0.3
                0.2
                0.1
               0.08
               0.06

               0.04
               0.03
               0.02
               0.01
                  0.01
• RAGWEED
OLYCOPODIUM
 0.003 0.006 0.1
0.03  0.06  1
   Figure 24.   Comparison of experimental settling efficiencies with
                calculated ones.
                                      71

-------
0
cc
Q 0.5
Z
w _
^ 0 0.1
£ P
DC <
X UJ
01 O
i ill'11! ' ' ' \ ' ' 'X
' OLYCOPODIUM ^A / -
SPORES /
%o° °^ AA
f & °° ~-
: ,0/e -
' / o AMETHYLENE
' / o° BLUE ' URANINE "
/ i , 1 i i i i 1 i i __i — 1 i i i i
                            0.05  0.1
0.5    1
                       STANDARD DEVIATION a (-)
                       CALCULATED BY EQS.(1)  AND (2)
Figure 25.  Comparison of experimental and calculated standard deviations
           of concentration ratio.
j
T
>\
-------
REFERENCES

 1.  Yoshida, H., T. Osugi,  H. Masuda,  S.  Yuu,  and  K.  linoya.
     Kagaku Kogaku Ronbunshu 2:336,  1976.

 2.  Yoshida, H., T. Osugi,  H. Masuda,  and K.  linoya.   Zairyo:
     J. Soc. Material  Sci.  Japan.  25:667,  1976.

 3.  Ushiki, K., K. Kubo,  and K.  linoya.   Kagaku  Kogaku Ronbunshu
     3:172, 1977.

 4.  Hess, J.L.  J. Fluid  Mech.  60:225,  1973.

 5.  Lewis, W.,  and R.J. Brun.   NACA Tech. Note 3658,  1955.

 6.  Langmuir,  I., and K.B.  Blodgett.   U.S.  Army  Air  Force  Tech.
     Rep. No.  548, 1946.

 7.  Brun, L.D., and M.  Vasseur.   Rech.  Aeronaut.  15:1, 1948.

 8.  Ranz, W.E., and J.B.  Wong.   Ind.  Eng. Chem.  44:1371, 1952.

 9.  May, K.R.,  and R. Clifford.   Ann.  Occup.  Hyg.  10:83, 1967.

10.  Gregory,  P.H., and Q.J. Stedman.   Ann.  Appl.  Biol.,  40:651,
     1953.

11.  linoya, K.  In: Fine  Particles,  B.Y.Liu,  ed.  Academic  Press,
     New York,  1976.   p 24.

12.  Yuu, S.,  N. Miyake, and K.  linoya.   Kagaku Kogaku Ronbunshu
     1:115, 1975.

13.  Strand, T.  J. Aircr.  4:466,  1967.

14.  Yuu, S.,  and K. linoya.  Kagaku Kogaku 34:427,  1970.

15.  Rosenhead,  H.  Laminar Boundary Layers.   Oxford  Press,  1963.
     p. 114.

16.  Yuu, S.,  and K. linoya.  Kagaku Kogaku 35:1251,  1971.

17.  Yoshida,  H., et al.   J. Chem.  Eng.  Japan 11:48,  1978.
                                73

-------
                             PAPER 4


        SIZING SUBMICRON PARTICLES WITH A CASCADE IMPACTOR
                         MICHAEL J. PILAT
                  DEPARTMENT OF  CIVIL  ENGINEERING
                     UNIVERSITY OF WASHINGTON
ABSTRACT
     The UW Mark 3-4 Source Test Cascade Impactors and associated
sampling train have been designed, constructed, and used for
measuring the size distribution over the approximately 0.02 to
20 ym aerodynamic range.  The UW Mark 4 Cascade Impactor utilizes
low absolute gas pressure which results in large Cunningham cor-
rection factors and accordingly enables sizing of particles of
0.02 to 0.2 ym diameter.  The Mark 3-4 sampling train includes
the UW Mark 3 and Mark 4 Cascade Impactors followed by a 90 mm
diameter filter, a low pressure drop tabular coiled condenser,
a two-stage high vacuum pump, and an instrumental control box
for pressure and temperature gauges, heater controls, and valves.
The UW Mark 3-4C Cascade Impactors operate around 0.4 to 0.5
acfm whereas the UW Mark 3-4D model has a gas sampling flow rate
in the 1.6 to 1.8 acfm  (stack conditions) range.  Particle size
distributions measured at emission sources including the J.E.
Corette Power Plant  (pulverized coal-fired boiler), UW Power
Plant  (pulverized coal-fired boiler), and Kearny Power Plant
(Pratt and Whitney oil-fired gas turbine) are presented.

INTRODUCTION

     Cascade impactors have been used since about 1968 to measure
the in-stack distribution  (in the 0.2 to 20 ym diameter range)
emitted from stationary sources.  Research at the University
of Washington has resulted in the development of the University
of Washington Source Test Cascade Impactor  (models Mark 12
3, 4, 5, 10, and 20) which have been or are being patented by
Pilat1 and licensed out by the University of Washington  (to Pol-
lution Control Systems Corporation of Renton, WA) for manufac-
ture and commercial sale.
                                74

-------
     This paper reports on  the Mark  3-4  Source  Test  Cascade  Impac-
tor sampling train and its  application  for  sizing  particles
emitted from electric utility power  plants.  Pilat, Ensor,  and
Bosch2 reported on the development and  use  of  the  Mark  1  and
2 UW Source Test Cascade  Impactors.   The Mark  1,  2,  3,  and 5
models size particles in  the general range  of  0.2  to 20 urn aero-
dynamic diameter.  The Mark 5 model  has  11  stages  followed by
a filter and is designed  for use  at  high particle  concentrations
such as exist at the  inlet  to control equipment.   Pilat3  described
the earlier development work on  the  Mark 4  impactor.  Pilat,
Fioretti, and Powell1* reported on the sizing of particles (in
the 0.02 to 20 ym diameter  range)  emitted from  coal-fired power
boilers using the Mark 3-4  cascade  impactor  sampling train.

THEORY OF CASCADE IMPACTORS

     Cascade impactors fractionate  the  particulate matter from
an emission source  into size  increments  by  inertial  impaction
of the particles on  a collection  surface.  This occurs  at suc-
cessive stages within the impactor.   The resulting index  of
particle size is traditionally  expressed by the particle  size
collected with 50%  collection  efficiency for each  stage,  d  •
The particle diameter has been  related  to the  Stokes inertial
impaction parameter  Y which is  defined  by Ranz  and Wong5  as
 c?dp  vj
  18u  D.
                                                               (1)
where  C  is  the  Cunningham correction factor,  p the particle den-
sity,  dp the  particle diameter,  Vj the gas velocity in the jet,
u  the  gas viscosity and Dj the jet diameter.   Solutions of the
equation of particle motion at various magnitudes of ¥ and experi-
mental studies  have shown that the Stokes inertial impaction
parameter at  50%  collection efficiency (Yso)  for a particular
diameter (d50)  ranges between 0.12 and 0.17 for circular jets.
These  values  were originally reported by Ranz and Wong5 and later
confirmed by  McFarland and Zeller.6  Solving  for the particle
diameter from equation (1) gives
fisi
t
                               .
                          Cp  V.
                            P  3
                                  h
                                                               (2)
 Substituting  an average value of 0.145 for Y50 provides an equa-
 tion  for  d50,
                                75

-------
                     IB o
                          2.61p D.
                                                               (3)
Equation (3)  provides an expression which relates  the  cascade
impactor stage d50 and the impactor parameters.  These param-
eters can be appropriately altered to provide an even  distri-
bution of dso's throughout the impactor stages.  For sizing  of
submicron particles, the Cunningham correction factor  becomes
of particular significance due to the physical limitations  in
further altering the other impactor parameters.  The Cunningham
correction factor C is defined by an equation reported by Davies7
            C = 1 +
2X
d
                     5 0
[l.
275 + 0.40 exp
(-1.
                 10
(4)
where X is the gas mean free path.  Thus, it can be seen  by  exami-
nation of equations  (3) and  (4) that it is possible to  select
the appropriate magnitudes of the impactor parameters necessary
to provide a stage dso as low as 0.02 Mm.  Assuming a particle
density p of 1 g/cm3 and substituting into equation (3) provides
an equation for the  aerodynamic cut diameter daso

                                     h
                    da
                      5 0
2.61y D.

  C V.
     D  J
                      (5)
UW MARK 3-4 CASCADE IMPACTOR INSTRUMENTATION

Sampling Train

     The UW Mark 3-4 Cascade Impactor sampling train  is  shown
in Figures 1 and 2.  Figure 1 illustrates the Mark 4D and  90
mm filter located  inside the stack, whereas Figure 2  shows them
external of the stack.  Heaters can be used to maintain  the Mark
4D and filter holder at the desired temperatures.  The Mark 4C
cascade impactor can also be used with the Mark 3-4D  sampling
train.  The UW Mark 3-4 Cascade Impactor sampling train  includes
a UW Mark 3 impactor, a UW Mark 4 impactor, a filter  holder,
a condenser, a leakless vacuum pump, a dry gas meter, and  a'con-
trol box.  The train can also be used with a BCURA cyclone up-
stream of the Mark 3 impactor.  When physical constraints  such
as too small a diameter of the sampling port exist, the  sampling
train can be arranged with the Mark 4 located outside the  stack
External heaters can be used to maintain the Mark 4 and  filter
holder temperature above the dew point.

     The control unit contains the  instruments for measuring
the temperature and gas pressures,  heater control, and pressure
tap valves.  Pyrometers are used for the temperature  readouts
measured by type J  (iron-constantan) thermocouples.   Thermocoupl
                                    es
                                76

-------
LJCURA
CYCLONE
MARK 3
IMP ACTOR
                                           90 mm
                              MARK 4      FILTER
                              IMPACTOR     HOLDER
  GAS FLOW
                            TO
                            CONTROL BOX
              (Tt) THERMOCOUPLE
               ?y) PRESSURE TAP
                                                   STACK WALL
                                                      trr::
                                                        ooooooooo
                                                          CONTROL BOX
                                                                                         CONDENSER
                                                                                DRY GAS
                                                                                METER
                                                                                                   VACUUM PUMP
                          Figure 1. U. of W. Mark 3-4D cascade impactor sampling train schematic.

-------
     BCURA
     CYCLONE
MARK 3
IMPACTOR
oo
                            3.
                            S
                            r
        GAS FLOW
            THERMOCOUPLE
            PRESSURE TAP
                                    STACK WALL    TO
                                                  CONTROL BOX
                        STAGE
                        PRESSURE
                        TAPS
                                                    ©T®T©  MK 4 IMPACTOR
                                                                            90 mm FILTER HOLDER
                                                                               HEATING
                                                              INSULATION OR \  MANTLE
                                                              HEATING TAPE
                                            CONTROL BOX
                                                         DRY GAS
                                                         METER
                                                                                                     VACUUM PUMP
                           Figure 2. Mark 3-4D sampling strain with Mark 4D located outside the stack.

-------
are located for measurement of the gas  temperature  inside  the
stack, at the Mark 4 inlet, Mark 4 outlet and  filter outlet.
Gas pressures are measured at all Mark  4 jet stages, the filter
inlet, and the filter outlet.  The gas  velocity  and static  pres-
sures are indicated by Dwyer Magnahelic gauges.   The external
heaters for the cascade  impactors and/or filter  holder  are  con-
trolled by rheostats housed in the control  unit.

UW Mark 3 Cascade Impactor

     The UW Mark 3 Cascade Impactor has 7 stages  followed by
a filter holder (47 mm diameter filters).   Figure 3 presents
a graph of the Mark stage da50's  (calculated)  as  a  function of
the gas volumetric gas sampling rate at stack  conditions (as-
suming a gas pressure of 2S.92 in. mercury).   The number of jets
per stage and the stage  jet diameters are presented in  Figure 3.


UW Mark 4C Cascade Impactor

     The UW Mark 4C Cascade Impactor has jet stage  and  collection
plate dimensions similar to the Mark 3 model such that  the  cy-
lindrical casing diameter is about 2.9  in.  (will  fit through 4
in. diameter pipe sampling port).  However, the  Mark 4C has gas
pressure taps on the jet stages.  Also  the  Mark  4C  has  a unique
arrangement of jet hole  diameters and numbers  per stage such
that the gas velocity does not reach Mach 1 (sonic  velocity)
on any one stage until an upper limit gas sampling  rate is  reached,
This upper liir.it gas sampling rate is about 0.5  cfm for the Mark
4C.  With this lower gas sampling rate, a 47 mm  diameter filter
holder can be used.

UW Mark 4D Cascade Impactor

     The Mark 4D Cascade Impactor model was designed in 1974
to have approximately 2  to 3 times the  gas  sampling flow rates
of the Mark 4C  (or about 1 to 1.8 cfm at stack conditions).
The Mark 4D has a jet stage of about 3.55 in.  diameter  and  a
cylindrical casing of 3.95 in. diameter and thus requires  a mini-
mum 5 in. diameter pipe  sampling port.  Copper tubing of 1/8-
in. diameter is connected to the pressure taps on each  jet  stage.
This pressure tubing is  connected to the pressure gauges in the
control box.

     For collecting those particles passing the  last stage  of
the Mark 4D, a 90 mm filter holder is used. This 90 mm filter
holder was designed and  constructed at  the  UW.  The condenser
is connected to the sampling probe by a Teflon lined flex  hose.
The condenser is to condense and collect water vapor and other
condensable vapors.  The condenser is a 3/4-in.  diameter stain-
less steel tube coil with a built-in water  trap.  It employs
dry ice as a coolant and is capable of  handling  a 5.0 scfm gas


                                79

-------
            1.20
             102
           £
           a.
           6
           in
           Q
           Ul
o
o

<
           Q
           O
           cc
           o
           cc
             10
             10°
             IO-
   I    i
                 FOR UPPER CURVE IN GROUP T = 500 °F

                -FOR MIDDLE CURVE IN GROUP T = 300 °F

                 FOR LOWER CURVE IN GROUP T = 100 °F
                                              I
               10
                rl
   3   4567  8910°

FLOW RATE, Q, cfm
                                             C/3
                                          Ul  111
                                          C3  "'

                                          V)  Z

                                          1   1
                                                    3  12
                         4  90
                         5 110
                                                    6  110
                                 CC
                                 111

                                 LLJ
                                                            — HI
                                                            Q I
                                 0.7180
                         2   6   0.2280
                                 0.0960
                                                 0.0310
                                                 0.0200
                                 0.0135
                         7  90  0.0100
          Figure 3. Calculated aerodynamic cut diameters for U. of W. Mark 3 stages.
flow  rate.   A two-stage,  leakless vacuum pump is used  with the
Mark  3-4.D sampling train.   A Rockwell  Model 250 dry  gas meter
with  temperature compensation to 70°F  is used to measure the
volume  of gas sampled  and  the gas sampling flow rate.

BCURA Cyclone

      A  BCURA  (British  Coal Utilization Research Association)
Cyclone is used to collect the larger  sized particles  which at
the higher particle  concentrations  can overload the  inlet par-
ticle collection plates of the Mark 3  impactor.  The BCURA Cyclone
is located at the inlet of the Mark 3  impactor, as  illustrated
in Figure 1.  The particulate sample is collected  in the hopper.
                                  80

-------
When physical constraints  hinder  the use of a 90°  angle probe,
the BCURA Cyclone  offers a convenient approach for enabling the
sampling nozzle  to be  faced upstream.  The BCURA Cyclone (as
commercially available from Pollution Control Systems Corporation,
Renton, WA) can  be used in sampling  ports of 4 in. or larger
diameter  (this commercially available model is slightly modified
from the British model).

     The equation  for  calculating the aerodynamic cut diameter
da5o of the BCURA  Cyclone  has  been reported by Hawksley, et al.,8
                     da
                       5 0
                            18  K a.p  D
                                c i
                               P  Q
(6)
where  ai  is  the  cross-sectional area of the cyclone inlet,  D
the  cyclone  body diameter,  y the gas viscosity,  p the particle
density  (assumed to be unity),  Q the gas volumetric flow rate
through  the  impactor,  and Kc a  dimensionless cyclone constant.
Kc  is  defined  by the equation

                     K  = X/L                                  (7)
                      \f
where  L  is the cyclone length and X is the "range"  of the par-
ticles.   The variable X is  defined by the equation

                     X = u V/g                                 (8)

where  u  is the Stokes velocity  of the particle,  V is the fluid
velocity  and g the acceleration of gravity.

     The  aerodynamic cut diameter da5 0 for the BCURA Cyclone
as  a function  of the gas sampling flow rate at stack conditions
is  presented in  Figure 4.

UW MARK 3-4  CASCADE  IMPACTOR  SAMPLING  PROCEDURE

Pre-Test Preparation

     Prior to  a  particulate  source  test,  certain  information
about  the  emission source should  be  known.   Since the  aerodynamic
particle diameters  (d50's) of the  impactor  stages are  dependent
upon the gas flow rate  through  the  impactor,  approximate  values
for the exhaust  gas  temperature  and  volumetric flow  rate  should
be known.  From  this information,  a  jet  stage  sequence can  be
chosen to provide an even distribution of  particles  throughout
the impactors  for the particle  size  range  expected.

     To reduce the tare weight  for  the particulate  collection
plates, 0.002  in. thick stainless  steel  inserts are  cut  and formed
for the impactor plates.  The inserts  must  be  conditioned for
                                81

-------
    10.0
                                                           10.0
                        ACFWI AT STACK CONDITIONS


            Figure 4. BCURA cyclone aerodynamic cut diameter versus gas
                   sampling rate.
the particular emission source.  They  are  first baked at a tem-
perature slightly higher than  the  expected exhaust gas tempera-
ture to alleviate the possibility  of weight loss due to evapora-
tion of surface impurities.  If  the particulate matter to be
sized is of a non-adhesive nature  (e.g., coal dust)  the collec-
tion inserts can be greased with a thin  layer of an adhesive
such as Dow Corning High Vacuum  Grease prior to baking.  This
minimizes bounce off and re-entrainment  of particles within the
impactor.  After the baking process the  inserts and filters are
desiccated for at least 12 hours and weighed with an accuracy
of ± 0.01 mg.  They are then stored in marked petri dishes and
are ready for shipment to the  sampling site.  Blank inserts are
prepared in order to identify  weight changes caused by reasons
such as weighing balance out of  calibration or grease volatiliza-
tion.

     Certain consideration must  also be  given to the physical
restrictions of the sampling site. A  probe length must be chosen
to be compatible with the particular stack or exhaust duct to
be tested.  The size and location  of the actual sampling plat-
form can also affect the lengths of reinforced flex hose required
to connect the components of the sampling  train.

     Prior to testing, it is important to  thoroughly clean the
particulate sizing components  of the train.  An ultrasonic cleaner
is recommended for cleaning the  impactor jet stages.
                                82

-------
Test Procedures

     With the impactors cleaned  and  loaded,  the  sampling  train
is assembled as described above.   Temperature  measurements  are
performed and the gas humidity  is  calculated by  the  wet bulb-
dry bulb method.  A type S pitot tube  is  used  for  velocity  head
and stack static pressure measurements.   A velocity  profile
across the duct is selected  for  isokinetic sampling.

     When the test parameters have been measured and calculated,
the probe is inserted inside the stack with  the nozzle facing
downstream.  Sufficient time (at least 15  minutes) is allowed
to pre-heat the impactors and filters  to  stack temperature.
The probe is then rotated so that  the  nozzle faces upstream and
the test is started.

     After an isokinetic sampling  rate has been established,
pressure measurements for the various  stages of the Mark  4  impac-
tor are made and recorded.  After  all  pressure readings have
been recorded, the pressure at  the filter  inlet is monitored
in order to detect an overloading  of the  filter.   The tempera-
ture in the stack and at the impactor  outlets  is also monitored
and recorded on the data sheet.

     Upon completion of the  test the probe is  removed from  the
stack and allowed to cool.  The  impactors  and  filter holder are
disassembled and the collection  inserts and  filter are carefully
removed and stored in the appropriate  petri  dishes.  The  cyclone
catch is stored in a marked petri  dish and the cyclone is washed
with acetone.  The wash liquid  is  also stored  in a sample bottle.

Post-Test Procedures

     The collected samples  (inserts  and filters) are first  baked at
250°F to drive off any moisture  which  might  have been collected
in return shipment.  The wash solutions are  evaporated at slightly
elevated temperatures in cleaned and tared aluminum  dishes.
They are then desiccated for at least  12  hours and weighed.
The particle weights are then recorded and used  in the computer
program for data reduction.

     The data reduction computer program  RASS  is used to  cal-
culate size distributions, mass concentrations and other  per-
tinent data to be used  in the final  analysis.  It  also generates
input information to be used in a  particle collection efficiency
program which calculates the collection efficiency as a  function
of particle size using  data  from simultaneous  inlet  and  outlet
tests.  Figure 5 presents a  computer  flow diagram  for the data
reduction program which illustrates  the calculation  procedures.
                                83

-------
oo
        No. of Holes
        Per Jet Stage
              Absolute Stage
              Pressure
              (in. Hg)
 Hole Diameters
 Per Stage
 (in.)
                 40.
            "jet
                    imp.
                                                                    T;OKS
                                                                       1 duct
                                                                                                 Ma;r -= 2S.9
                                                                                                     J
                                                                                                          R = 8.31 x 10'
                                                                      VISCOSITY
                                                                      ^ = 63 + 0.40T(°K)10-6
        ^impactor
        A WEIGHTS FOR EACH COLLECTOR
        PLATE PLUS FILTER
                                                 pp = 1.0	«P
                                                    = 0-145
                                                                        (I    M
                                                                                                           P = 1  ATM
                                                     AIR MEAN FREE PATH

                                                      , _  M(82.057)T
                                                                                                         0.499 pM
                                                                                                                   8RT
                                                                                                CUNNINGHAM i CORRECTION
                                                             V
                                          jet
     CUMULATIVE SIZE DISTRIBUTION BY WEIGHT

WT total on collection
     plates with d50  d50 plate x       % BY WEIGHT
	(100) = LESS THAN
                  WT
                    total
                                   d50 FOR PLATE X
                                                              	^  \]\l j
                  SUBROUTINE:
                  LEAST SQUARES FIT FOR STRAIGHT LINE
                  THROUGH DATA (LOG NORMAL DISTRIBUTION),
                  95% CONFIDENCE LIMITS
                                                                                  ITERATIVE
                                                                                  LOOP
                                                          C = 1 +-F  1.257 + 0.40e
                                                                    (-'•'•
                                                                                        1 meter
                                                                                 1 total
                                                                                        V
                                                                                         meter-
                                                                  CONCENTRATION (GRAINS/SCF)
                                                                                                                   (15.43)
                                                                                                           520° R
                                                                                                                 'meter
                                                                                             p
                                                                                             rmtr
    % BY-WT-LESS-THAN
    FOR 6 JET STAGES
              MASS MEAN
              DIAMETER
STANDARD
GEOMETRIC
DEVIATION
PLOT OF LN. PARTICLE DIA.
vs % BY-WT-LESS-THAN
(WITH 95% CONFIDENCE
LIMITS + STRAIGHT LINE FIT)

           PRINTOUT
d50 FOR
EACH STAGE
CONCENTRATION
FOR TEST
                                      Figure 5. Computer f/ow diagram for reduction of U. of I/I/. Mark
                                               3 and Mark 4 cascade impactor test data.

-------
PARTICLE SIZE DISTRIBUTION RESULTS

J.E. Corette Power Plant

Boiler and Electrostatic Precipitator  Description—

     Unit No. 2 at the J.E. Corette  Power  Plant, Billings, MT,
burns pulverized coal in a Combustion  Engineering  boiler  rated
at 163 MW electrical output.   Sub-bituminous  Grade C  coal having
a gross heating value of 8,600 Btu/lb  and  a sulfur content of
0.7% is introduced in a tangential firing  (swirling)  pattern
from 16 burners located at four elevations in the  boiler  corners.
Combustion gases leaving the unit typically contain 80% of the
total ash load and pass through a regenerative air preheater
before entering a Research-Cottrell  electrostatic  precipitator.
The precipitator is designed for 600,000 acfm gas  flow at 300°F
and 96% by weight particulate  collection efficiency.

Sampling Site Description—

     The inlet sampling site was located on the top of a  short
horizontal section of duct connecting  the  air preheater and the
precipitator.  The 4 in. diameter sampling port used  was  located
about 0.34 equivalent duct diameters downstream and less  than
0.1 diameters upstream from major gas  flow disturbances.   The
arrangement of this port necessitated  vertical insertion  of the
sampling equipment.

Sampling Technique—

     The Mark 3-4D Cascade Impactor  sampling  train was used for
the tests.  Due to certain physical  constraints at the sampling
ports, the Mark 4D impactor and the  absolute  filter were  located
outside the stack as illustrated in  Figure 2.  Efforts were made
through thermostatically controlled  heating tape and  insulation
to maintain the Mark 4D and the filter  at  stack temperatures.

     Due to the nature of the  aerosol  to be tested, the collec-
tion inserts were greased with Dow Corning High Vacuum Grease,
conditioned at 350°F and weighed.  All  other  pre-test and testing
procedures as well as the post test  analysis  were  performed in
the same manner as described above in  this paper.

     Five'tests  (A through E,  Tables 1  and 2)  were conducted
at the site during September 29 and  October 8, 1975.  The first
four were performed at the outlet sampling port while the last
(Test E) was at the inlet to the precipitator.  All of the tests
were conducted under normal operating  conditions with the excep-
tion of tests C and D in which the soot blowers in the super-
heater section were curtailed.
                                85

-------
Test Results—

     The distribution of particulate matter collected by the
various components of the Mark 3-4 sampling train  is presented
in Table 1.  The source test results are listed  in Table 2.
The Pearson Correlation Coefficient, listed in Table 2, is  a
measure of the degree of fit between the log normal approxima-
tion  (a linear regression) and the actual particulate size  dis-
tributions.  The Pearson Correlation Coefficient is more pre-
cisely defined as the ratio of the covariance to the square root
 TABLE 1.  DISTRIBUTION OF PARTICULATE WEIGHT COLLECTED BY  THE
  UW MARK 3-4 IMPACTOR SAMPLING TRAIN FOR J.E. CORETTE TESTS

Particulate weight, g
Test
A
B
C
D
E
BCURA cyclone
hopper & wash Mark III Mark IV
0.0514
0.0332
0.1182
0.1850
0.9984
0.0559
0.0617
0.0888
0.0883
0.1808
0.0015
0.0032
0.0023
0.0045
0.0024
Condenser
Filter trap & wash
0.0006 0.2142
0.0007 0.0298
0.0007 0.0348
0.0018 0.0018
0.0029 0.0076
Total weight
excluding
condenser
0.1094
0.0978
0.2100
0.2796
1.1845


TABLE
2. SOURCE TEST RESULTS
FOR J.E. CORETTE TESTS


Test
A
B
C
D
E

Mass mean
diameter,
ym
4.9
3.5
10.4
35.7
210.6

Standard
geometric
deviation
5.17
5.32
5.10
12.97
12.73

Pearson
Correlation
Coefficient
0.985
0.974
0.967
0.953
0.910

Condensed
Solid particle particle
concentration, concentration,
gr/dscf gr/dscf
0.064
0.052
0.110
0.192
3.151
0.126
0.016
0.018
0.001
0.033
                                86

-------
of the product of squares of  the  variation  in  X  and  the  variation
in Y.  The actual particulate  size  distributions for  each  test
are illustrated in Figure 6.

Discussion—

     The average size distribution  for  the  four  tests conducted
at the outlet of the precipitator (Tests  A-D)  shows  that 13.4%
of the particle mass is  less  than 1.0  ym  in diameter.

     The actual size distribution for  the inlet, Test E, shows
a marked skew to the right  for  particles  greater than about  0.8
ym in diameter indicating a decreasing  concentration  of  large
particles.  The mass mean diameter  for  this test,  calculated
from the log-normal approximation,  is  indicated  as 210 ym.   The
lack of additional actual data points  for particles  greater  than
4.0 ym has skewed the log-normal  approximation to the left and
given it a greater relative slope.   Extrapolation of  this
curve from the last actual  data point  of  7.5%  of the  cumulative
weight to the 50% points results  in the unreasonably  high  mass
mean diameter.  A further breakdown of  the  mass  which was  consoli-
dated in the last data point  (approximately 90%  of the total
mass) would eliminate the necessity of  extrapolating  the curve
to 50% of the cumulative weight and result  in  a  more  reasonable
mass mean diameter.  For this particular  test  the BCURA  cyclone
has a cut point diameter which was  too  small,  thus collecting
and consolidating too much  data into one  point.

     The vertical insertion of the  sampling train into both  the
inlet and outlet sampling ports meant  that  the UW Mark 3 and
4D impactors were oriented  in an  upside-down position.  Disas-
sembly of the impactors  after each  test showed that  some par-
ticles had fallen off the collection plates onto the  preceding
jet stages.  These jet stages were  cleaned  by  washing with dis-
tilled water and the particle weights  were  determined (after
evaporation to dryness)  and added to appropriate collection
stages.  However, the extra lab work caused by the vertical
sampling probe alignment could be obviated  by  either  a horizontal
or a right-side up positioning of the  impactors.

UW Power Plant

Description of Source—

     UW Power Plant Boiler  No.  5  is a  Riley Stoker Corporation
pulverized coal-fired boiler.   It has  a rated  steam capacity
of 120,000 Ib/hr with outlet  steam conditions  of 400  psig  and
600°F.  The exhaust gases from Boiler  No. 5 pass through a Re-
search-Cottrell electrostatic precipitator  with an overall design
efficiency of 94% for particulate matter.  The precipitator  is
designed for a volumetric flow rate of 50,000  acfm at 400°F.
                                87

-------
  10.0
              II    I
                                            I   I
1   I
E
6
in
D
OC
UJ
I-
ui
o
o
Q
O
cc
ui
<
at
u
cc
Q.
    0.1
    0.01
                           I
                                       TEST A   «  OUTLET
                                       TEST B   A  OUTLET
                                       TEST C   V  OUTLET
                                       TEST D   O  OUTLET
                                       TEST E   D   INLET
       0.01
                       1            10              50
                    % OF MASS LESS THAN STATED DIAMETER
             90
           Figure 6. Particle size distributions for tests A-E, J. E. Corette
                    Power Plant.
                                    88

-------
     The simultaneous samples were  taken  at  the  inlet  and  outlet
of the precipitator.  The  inlet  sampling  port  is located at  the
No. 5 Boiler exhaust duct  prior  to  entrance  into the precipitator.
The exhaust gases  flow  vertically upwards at the sampling  point.

Sampling Technique—

     The UW Mark 3-4 Cascade  Impactor  Sampling Train used  was
identical to the one described above.   The BCURA Cyclone,  the
Mark 3 and Mark 4  Impactors and  the 90 mm glass  fiber  filter
were inserted  inside the duct.   A Mark 4C was  used  at  the  pre-
cipitator inlet and a Mark 4D was used at the  precipitator out-
let.

     The pre-test  preparation, the  testing procedures  and  the
post-test analyses  were conducted in the  same  manner as described
above.  All pre and post test tasks were  performed  at  the  UW
Air Resources  Lab  since the UW power plant is  directly adjacent
to the Civil Engineering Building.   The two  tests reported  (A
and B) were simultaneous source  tests  performed  at  the inlet
and outlet of  the  electrostatic  precipitator.

Test Results--

     The size  distribution and collection efficiency results
are summarized in  Table 3. The  overall collection  efficiency,
including solid and condensible  matter, was  found to be 94.4%
and 90.3% for  the  two  tests performed.  The  particle size  dis-
tributions are presented in Figure  7.

Discussion--

     These tests demonstrated that  the Mark  3-4  impactor trains
were capable of simultaneous  particle  sizing (during the same
time period) at the inlet  and outlet of particulate control de-
vices.  Testing was performed at the inlet and outlet  of the
control device at  considerably different  gas sampling  rates pro-
viding particle collection efficiency  data as  a  function of par-
ticle size over a  0.07  to  3.5 ym size  range.

Kearny Generating  Station

Test Site Information—

     The primary objective of the source  tests at the  Public
Service Electric and Gas Company Generating  Station, Kearny,
NJ, was to determine the effect  of  three  different  fuel additives
upon the particulate size  distribution in the  exhaust  gas  from
an FT4C-1LF Pratt  and Whitney gas turbine engine.  The three
different smoke suppressing fuel additives injected into the
turbine fuel supply are listed  in Table 4.  To avoid any con-
flict as to the industrial designation of the  additives, they


                                89

-------
   10.0
10   in
Q    1.0
111

<
Q
H
D
O
o
Z

Q
O
oc
              TT
1     I
     0.01
                                                          I   I
        0.01    0.1        10           30              60        80

                  % OF MASS LESS THAN STATED DIAMETER


     Figure 7. Particle size distributions for U. of W. Power Plant.
                                  90

-------
TABLE 3.  SOURCE TEST RESULTS OF UW POWER BOILER TESTS

Particle mass concentration, gr/dscf Overall

Test
A-Inlet

A-Outlet
B-Inlet

B-Outlet
Mass mean
diameter ,
ym
25

12
23

34
Standard
geometric
deviation
12

12
9

21
Pearson
Correlation
Coefficient
0.92

0.91
0.91

0.90

Solids
0.708

0.033
0.784

0.050
particle
collection
Condensibles efficiency,
0.010
94.4
0.007
0.000
90.3
0.026

-------
             TABLE  4.   DESCRIPTION OF FUEL ADDITIVES
                     USED  FOR KEARNEY TESTS

Additive
Test designation
A None
B I
C I
D II
Additive metal content,
% by weight

6
6
5
1
	
.75
.75
.34
.48

Fe
Fe
Mn
Ba
                     III                      24.7 Mn
are defined as additives I, II and III.  Additive I was an  iron
based substance, additive II was an organic manganese-barium
compound and additive III was an organic manganese compound.
All additives were mixed with the fuel at a concentration of
approximately 50 ppm.

     The FT4C-1LF Pratt and Whitney gas turbine which was tested
at the Kearney Power Plant is one of two engines included in
a TP4-2LF Twin Pac gas turbine installation.  The two turbines
are located in opposite directions and simultaneously drive the
generator.  The generator is also capable of operation at approxi-
mately half power with one turbine either windmilling or decoupled
from the generator.  For all tests performed, turbine B was de-
coupled.

Test Schedule and Sampling Conditions—

     The tests were performed January 21-27, 1976.  The UW Mark
3-4 Cascade Impactor sampling train was arranged as shown in
Figure 2 with the BCURA Cyclone and Mark 3 Impactor located in-
side the stack and the Mark 4D Impactor and 90 mm diameter filter
holder outside the stack.  The overall test preparation and pro-
cedures were the same as described above with certain considera-
tions given to the extreme conditions to be faced in this test
To alleviate any problem with weight changes in the stainless
steel collection inserts due to the extreme temperatures, pre-
test temperature experiments were performed.  Type 304 stain-
less steel was found to exhibit a significant weight change due
to intergranular corrosion when baked at 950°F for a 2 hour
period.  Type 316 ELC (extra low carbon) stainless steel showed
negligible weight change due to the elevated temperature and
was chosen for the collection insert material.  All inserts
prebaked at 950°F for 2 hours, desiccated, and weighed, then
packed in marked petri dishes.

                               92

-------
Test Results—

     The results from  the  five  particulate  source  tests  are  pre-
sented in Table 5.  The mass  mean  diameters are  shown  to vary
from 0.13 to 0.21 ym.  Figure 8 illustrates the  actual particle
size distribution for  each test.   The  particles  sized  in all
five tests ranged from 0.03 ym  to  3.7  ym in diameter.  Excellent
correlation between the straight line  approximation  and  the
actual size distribution  is demonstrated by the  Pearson  Correla-
tion Coefficients listed  in Table  5.

Discussion—

     The source test results  indicate  that  the turbine fuel  ad-
ditives have a small effect upon the size distribution by mass
of the particulate emissions.   The most  apparent variation is
observed for the larger particles.  The  injection  of additives,
particularly the organic manganese and the  manganese-barium  ad-
ditives, created a greater percentage  of larger particles  (greater
than 0.3 ym diameter).  The additives  had only a slight  effect
upon mass mean diameter,  the  greatest  change being for the two
manganese additives.   The  convergence  of the size  distributions
in the 0.1 and 0.2 ym  diameter  range indicates an  insensitivity
for particles of this  size to the  additives.  Reduction  from
the industrial load schedule  to the minimum load schedule for
the turbine, with the  injection of iron  based additive in both
cases, resulted in a very  negligible change in the size  distri-
bution.

     Due to the particularly  high  exhaust gas temperatures  (about
800°F), the Mark 4D Impactor  was situated outside  the  stack.
The impactor and the exposed  portion of  the probe  were maintained
at an  elevated temperature by external heating.  Despite these
efforts, a substantial amount of weight  was obtained from the
probe  washes.  This weight is labeled  as probe wash  and  not  in-
cluded in the particulate  size  distribution since  the  exact
nature of this weight  is  not  certain.

     To alleviate such problems it is  recommended  that the con-
necting probe section  between the  Mark 3 and Mark  4  Impactors
be minimized and both  impactors plus any connecting  probes be
held at stack temperatures.
                                93

-------
1C.O
9  OUTLET
A  OUTLET
A  OUTLET
O  OUTLET
B  INLET
                                              TESTA
                                              TEST B
                                              TEST C
                                              TEST D
                                              TEST E
                 10   15     20    30   40   50   60    70  80   85
                        % OF MASS LESS THAN STATED DIAMETER

                  Figure 8. Particle size distributions, tests A-E, Kearney
                           Generating Station.
                                       94

-------
TABLE 5.  SOURCE TEST RESULTS FOR KEARNY TESTS

Test
A
B
C
D
E
Turbine
load
Ind.
Ind.
Min.
Ind.
Ind.
Fuel
additive
None
I
I
II
III
Mass
mean
diameter ,
ym
0.14
0.13
0.13
0.17
0.21
Particle mass concentration, gr/dscf
Standard
geometric
deviation
3.5
4.5
4.7
7.1
4.6
Pearson
Correlation Solids
Coefficient
0.96
0.99
0.96
0.99
0.97
0.0033
0.0023
0.0027
0.0014
0.0014
Condensibles
0.0025
0.0162
0.0039
0.0043
0.0040
Probe wash
--
0.0027
0.0052
0.0010
0.0021

-------
CONCLUSIONS

     An improved particulate sampling train was constructed  to
size particles emitted from coal-fired power boilers  in  the  range
of 0.02 to 20.0 pm in diameter.  The new components were  designed
and assembled to accompany the UW Mark 3 and Mark  4 Impactors.
It has been demonstrated that this equipment and technique  is
capable of in-stack particulate sizing for the 0.02 to 20 ym
diameter range.

     Two source test programs were performed on coal-fired  power
boilers at the J.E. Corette Power Plant, Billings, MT, and  at
the University of Washington Power Plant, Seattle, WA.  A par-
ticulate source test was also performed on an oil  fired  turbine
at the Kearny Generating Station, Kearny, NJ.  It  has been  shown
that the new sampling train is capable of sizing particles  at
both the inlet and outlet of particulate control devices.   It
was also demonstrated that two such sampling trains can be  simul-
taneously operated at the inlet and outlet of a particle  control
device on a coal fired power boiler during the same sampling
period to evaluate the collection efficiency as a  function  of
particle size.
ACKNOWLEDGEMENTS

     This research was supported by the Electric Power Research
Institute, Palo Alto, CA.  The assistance of G. Fioretti, G.
Raemhild, A. Thoreen, and E.B. Powell with the field testing
is appreciated.
REFERENCES
1.


2.


3.



4.
5.
Pilat, M.J.  Source Test Cascade Impactor.
3,963,457, 1972.
U.S. Patent
Pilat, M.J., D.S. Ensor, and J.C. Bosch.  Source Test Cascade
Impactor.  Atmos. Environ. 4:671-679, 1970.

Pilat, M.J.  Submicron Particle Sampling with a Cascade
Impactor.  Paper No. 73-284, presented at APCA Annual Meetinq
Chicago, IL, 1973.

Pilat, M.J., G.M. Fioretti, and E.B. Powell.  Sizing of
0.02 to 20 Micron Diameter Particles Emitted from Coal-Fired
Power Boiler with Cascade Impactors.  Presented at APCA
Annual Meeting, Vancouver, B.C., 1975.

Ranz, W.E., and J.B. Wong.  Jet Impactors for Determining
the Particle Size Distribution of Aerosols.  AMA Arch
Hyg. Occup. Med. 5:464-477, 1952.                    '
                               96

-------
6.   McFarland, A.R., and H.W-  Zeller.   Study  of  Large Volume
     Impactor for High Altitude Aerosol  Collection.   USAEC TLD
     18624, 1963.

7.   Davies, C.N.  Definitive  Equations  for  the Fluid Resistance
     of Spheres.  Proc.  Phys.  Soc.  London  57:259-270, 1945.

8.   Hawksley, P.G.W., S. Badzioch,  and  J.H. Blackett.  Measure-
     ment of Solids  in Flue  Gases.   British  Coal  Utilization
     Research Association, Leatherhead,  Surrey, 1961.  214 p.
                                97

-------
                             PAPER  5
     EXPERIENCE  IN  SAMPLING URBAN AEROSOLS WITH THE SINCLAIR
               DIFFUSION BATTERY AND  NUCLEUS  COUNTER
                          EARL  0.  KNUTSON
                          DAVID SINCLAIR
               ENVIRONMENTAL MEASUREMENTS  LABORATORY
                     U.S.  DEPARTMENT  OF  ENERGY
ABSTRACT

     The Sinclair diffusion battery and nucleus counter have
been coupled to a data acquisition and control system for auto-
mated monitoring of ambient aerosol size distribution and number
concentration in New York City.  Previous versions of this equip-
ment required recording of data manually or by strip chart.
The present version also incorporates a newly-designed rotary
sequencing valve and a nucleus counter with increased cooling
capacity and continuous alcohol feed.  Unattended operation for
three days or more is possible.

     Diffusion battery penetration data are obtained on computer-
compatible punched tape at 10, 20, 60 or 120-minute intervals.
Our standard practice is to resolve these data into an eight-
class particle size histogram spanning the diameter range 32
to 322 nm.  Twomey's nonlinear iterative algorithm is used for
this calculation.

     Approximately 1000 size spectra of the New York City urban
aerosol have been obtained with the present system in addition
to 233 spectra that were obtained with an earlier version.  Typi-
cally, the geometric mean diameter and geometric standard devia-
tion are in the ranges 25 to 40 nm and 1.8 to 2.0 nm, respec-
tively.  The spectra typically show a slight positive skew
relative to the log normal.

INTRODUCTION

     This paper is a report on the status of the Sinclair dif-
fusion battery and nucleus counter and an account of our exper-
ience with this apparatus.  Several events of significance have


                               98

-------
occurred since  the  last  status  report,  given over  two years  ago:1
fourteen replicas of  the diffusion battery were manufactured
by a commercial  firm  and distributed to subscribers  worldwide;
the screen version  of the diffusion battery is now commercially
available  (Thermo-Systerns,  Inc.,  St. Paul, MN); we have  made
approximately 1000  measurements of urban aerosol size distribu-
tions and have  made a number  of changes in the apparatus based
on that experience.

     The bulk of the  information  in  the earlier  report,1  includ-
ing calibration data,  remains valid.  The  reader is  referred
to that report and  its references  for descriptions of  the basic
components of the system.   Some additional information concern-
ing the system will appear  in a forthcoming  article  on the New
York summer aerosol.2  The  present  paper will  describe the modifi-
cations made to date,  new peripheral equipment  added  for  control
and data acquisition,  data  processing including  the  calculation
of size distributions from  observed  diffusion  battery penetra-
tions, and the  use  of the system.

MODIFICATIONS TO PREVIOUSLY-DESCRIBED EQUIPMENT

Principal Dimensions  of  the Diffusion Battery

     There now  exist  two manufacturing  runs  of  the Sinclair  dif-
fusion battery  and  these differ significantly  in their principal
dimensions.  The first sets of  diffusion batteries were made
using diffusional separating  elements supplied  by  the Brunswick
Corp. of Chicago.   Brunswick  used  the term "Collimated Holes
Structures" to  identify  these elements.  Each  element consisted
of a circular disk, 4.44 cm in  diameter, containing  14,500 holes
of 230 micrometers  diameter.  Eighteen  disks of various  thick-
nesses were used in the  batteries.3

     The second manufacturing run,  which included  the  14  bat-
teries distributed  to subscribers,  made use  of  diffusional ele-
ments manufactured  by Nuclear Metals of Concord, MA.   The ele-
ments were referred to as "Honeycomb Structures" by  the  manu-
facturer.  These elements were  disks, also 4.44  cm in  diameter,
but they differed from the  Brunswick version in the  number and
size of holes in each disk.   The  Nuclear Metals disks  contain
9,750 parallel  holes  of  380 micrometers diameter.

     Table 1 shows  the principal  dimensions  of  the original  and
recently manufactured diffusion batteries.

Sequencing Valve

     In the previous  version  of the automated  Sinclair diffusion
battery, air flow through the various stages of the  battery  was
controlled by a bank  of  13  solenoid valves which were opened
in sequence by means  of  a cam and microswitch  assembly.   The

                                99

-------
          TABLE 1.  PRINCIPAL DIMENSIONS OF  THE  CHS  AND
                 HS SINCLAIR DIFFUSION BATTERIES

Segment
No.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
Tap*
No.
1
2
3
4
5
6
7

8

9


10



11
Segment Thickness (cm)
CHS**
0.343
0.310
0.640
1.029
1.313
1.880
2.57
2.61
1.228
2.56
2.55
2.60
2.58
2.56
2.58
2.56
2.62
2.57
HS
0.318
0.318
0.635
0.952
1.270
1.905
2.54
2.54
1.270
2.54
2.54
2.54
2.54
2.54
2.54
2.54
2.54
2.54

       CHS:   "Collimated Holes Structures" manufactured
              by Brunswick Corp.

       HS:    "Honeycomb Structures" manufactured by
              Nuclear Metals.

        *  Indicated tap follows the corresponding seg-
           ment in the left column.

       **  The CHS version was used in all measurements
           described in this paper.

valves were noisy, both acoustically and electrically.  The elec-
trical noise was troublesome, since it caused spurious signals
in the digital circuitry used to record data.  A second disad-
vantage of the arrangement was that it was not amenable to ex-
ternal control, such as timing signals for synchronization pur-
poses .

     Based on our experience, specifications were drawn up for
a new sequencing valve.  Particular attention was given to the
requirements  of aerosol mechanics and to compatibility with
digital data-handling circuitry.  The valve was designed and
constructed by the Instrumentation Division at EML.
                               100

-------
     The new valve  is  shown  in Figure 1.   A configuration  is
used in which 15 ports are arranged in a  circular pattern.  A
drive motor, which  runs continuously, is  coupled to the  valve
rotor through a gear  train and an electromechanical clutch.
Each actuation of the  clutch causes the rotor to advance 1/15
of a revolution, stepping the valve to the next port.

     To minimize aerosol losses,  the valve was designed  with
relatively large flow  passages and a minimum number of changes
in flow direction.  The smallest  passage  is the straight passage
through the rotor which has  diameter of 0.64 cm.   Downstream
of the rotor, the 15 ports are connected  to a toroidal manifold,
with relatively large  internal dimensions.

     The time required to step the valve  is one second so  that
the interruption of flow is  negligible.  The clutch is activated
by momentarily  (1/20  to 1/4  second)  grounding a line from  the
clutch solenoid, which is powered by an on-board 24 V DC power
supply.  The solenoid  current is  only 220 mA and no interference
with digital data circuitry  has been noted.

     The fifteen ports include three spares, which are used to
obtain clean air readings  (through an absolute filter) at  the
beginning and end of  each measurement cycle and to obtain  a re-
dundant reading of  the diffusion  battery  inlet concentration.
Table 2 shows the valve sequence  used in  the present system.
Port 0 is used as a "home" position, where the valve starts and
ends each measurement  cycle.

Continuous Flow Nucleus Counter

     As described elsewhere, "* the continuous flow nucleus  counter
utilizes ethyl alcohol as the working fluid which condenses on
the aerosol particles.  During the first  extended outdoor  test
of the nucleus counter, in August of 1976,  we found that the
alcohol also served as a good desiccant.   As long as the alcohol
is fresh, it dehumidifies the air sample  stream.   However, after
two to three days in  humid weather,  the alcohol becomes  so diluted
with water that it  is  no longer an effective desiccant.  Atmos-
pheric water vapor  then enters the cold tube, where it forms
frost and blocks the  light beam.

     To counter the formation of  frost, fresh alcohol is contin-
uously supplied to  the alcohol tube  of the  nucleus counter.
The alcohol flows under gravity through a needle valve adjusted
to 150 cm3/day.  The alcohol tube overflow is collected  in another
receptacle, closed  to  the atmosphere.

     A second difficulty encountered in August 1976,  was that
of maintaining sufficiently  low temperature in the cold  tube
of the nucleus counter.  We  have  found that it is necessary to
                                101

-------
Figure  1. Sequential muft/port samp/ing valve.
                     102

-------
        	TABLE 2.  VALVE PORT ASSIGNMENTS

        Valve Port                 Connection

             0               Absolute Filter
             1               Absolute Filter

             2               Diffusion Battery inlet
             3               Diffusion Battery inlet

4
5
6
7
8
9
10
11
12
13
14
Diffusion Battery
tap no.
tap no.
tap no.
tap no.
tap no.
tap no.
tap no.
tap no.
tap no.
tap no.
tap no.
1
2
3
4
5
6
7
8
9
10
11

maintain -15°C  in  the  cold  tube  for proper nucleus counter opera-
tion.  In  the August sampling  session,  the temperature in the
equipment  shed  often reached 35°C  and we had to supply additional
cooling by means of an air  conditioner.  Since then, a Model
2 nucleus  counter  has  been  built incorporating additional cooling
capacity.  This version was found  to be marginally adequate in
hot weather.  To provide a  reserve of cooling power, Model 3
(now in preparation) will incorporate two-stage thermoelectric
elements to  increase the attainable temperature differential.

NEW PERIPHERAL  EQUIPMENT

Timing and Control Circuit

     Continuous cycling through  the diffusion battery taps pro-
duce more  data  than is needed  in most applications.  Single
cycles initiated periodically  give the  preferred mode of opera-
tion.  To  facilitate correlating aerosol data from the diffu-
sion battery with  other information, such as meteorological
variables, it is convenient to have these single cycles initiated
on the hour.

     The Instrumentation Division  at EML has devised a timing
and control circuit which provides the  desired control signals
to the rotary valve.   As indicated in the functional diagram,
Figure 2,  all timing is based  on counting pulses derived from
the 60 Hz power main.   Counting  commences from zero at the time


                               103

-------
 115V
 60 Hz
                                  RUN/
                                  STANDBY
                                  SWITCH
       TRANSFORMER
       AND CLIPPING
       CIRCUIT
       SCALER CHAIN,
       PULSE FORMING
3.1 SEC
                    1 PULSE/32 SEC
         PULSE
         COUNTING
         AND
         STEERING
                                                TO MULTIPORT VALVE STEP
                                                     HOME DETECTOR
                                                TO DATA RECORDER
                                                TO EAA
                                                    PRESET
              Figure 2. Functional diagram of timing and control circuit.

 when the Run/Standby control is switched  to  Run.   Cycles consist-
 ing  of fifteen 0.1-second pulses spaced 32 seconds apart are
 started at one-hour intervals to step  the multiport valve.  A
 provision is made to insure that the valve stops  at home position
 (port 0)  after each cycle.

      The same circuit also controls the data acquisition equip-
 ment and an electrical aerosol analyzer  (Thermo-Systems Model
 3030).   The latter is often run in conjunction  with the diffusion
 battery/nucleus counter for comparison.

      The  timing and control circuit has proved  to  be  reliable
 in two  separate four-week  periods of continuous operation.   The
maximum observed error  in  cycle initiation time, using  the tele-
phone company  time as  a standard,  was 5 seconds.   The important
point here  is  that the  timing  errors are  not cumulative,  since
the  power  company apparently adjusts its  generators periodically
to keep the  cumulative  number  of cycles on schedule.

      In addition to the hourly schedule,  the timing and control
circuit can  be set to  initiate cycles at  10,  20 and 120-minute
intervals.

Data Recording Apparatus

     The  Sinclair diffusion battery and nucleus counter generate
a large volume of data,  even when operated on hourly  cycles.
                                104

-------
Extended operation  is  feasible  only in conjunction  with  apparatus
for reliable recording  data  in  machine-readable form.  We  pres-
ently use a system  assembled by the EML Instrumentation  Division,
using some commercial  components and some  components which are
standard within our  Laboratory.   It is likely that  this  system
will change considerably  in  the near future to take advantage
of the rapid developments in commercial data handling  electronics.

     The main components  of  the present data recording apparatus
are two analog-to-digital conversion circuits,  a time-of-year
clock, a teletype  interface  and a teletypewriter.   The electronic
modules are housed  in  a standard full-width NIM bin, which also
houses the timing  and  control circuit.

     The analog signal  from  the nucleus counter is  converted
to digital form by  means  of  a voltage controlled oscillator con-
nected to a sealer.  A gating circuit keyed to the  timing  and
control circuit  (described earlier)  gates  pulses from  the  oscil-
lator into the sealer  during a  five second period starting 17
seconds after each  step of the  rotary valve.  The 17-second
period allows for  the  response  time of the nucleus  counter and
the five-second period  provides signal averaging.   The accumu-
lated count, which  is  directly  proportional to the  five-second
averaged analog voltage,  is  sent out to the teletypewriter on
the next step signal from the timing and control circuit.   A
second analog channel  is  normally used to  record data  from the
electrical aerosol  analyzer.

     The data are  recorded in the form of  six-digit integers.
The teletype produces  both a printed and a punched  tape  record
of the data.  Due  to a  local convention in data handling,  the
punched tape approach  is  the most direct method for us to  enter
data into our main  computer.

     Teletype systems  are widely used for  data  recording in our
Laboratory, mostly  in  temperature and humidity-controlled  indoor
environments.  We have  logged about  2,500  hours of  operation
in uncontrolled outdoor equipment sheds and we  find that the
reliability of recording  data varies with  the weather.   In cool
weather, the error  rate is of the order of one  mispunched  bit
per day (1 bit in ^100,000).  In hot weather,  the error  rate
may increase 1000-fold.   We  have found, however,  that  the  punch-
ing errors are of such  a  nature  that the actual numerical  values
are seldom affected.  By  reprogramming our tape reading  routine,
we find that even badly mispunched tapes can be read with  good
reliability.

     The main disadvantage of the teletype is that  it  is cumber-
some in field use.   It  is planned to replace the teletype  in
the near future with a  magnetic  tape cassette system.
                               105

-------
DATA PROCESSING

     A fully mechanized procedure has been developed for pro-
cessing the data from the Sinclair diffusion battery and nucleus
counter.  The input is punched paper tape from the teletype  and
the output is computer cards, one for each measurement cycle.
Each card is encoded with year-month-date-hour and eight values
of AN/A(loglOdp) from that hour's measurement.  The cards are
suitable for filing and subsequent statistical studies.  The
procedure also produces a printed summary, including a bar-graph
histogram, of each hour's results.

     A flow chart of the computer program used for data processing
is shown in Figure 3.  All elements of the program are straight-
forward, with the exception of the size distribution calculation.

     For analyzing diffusion battery data, we sought an algorithm
which would be well suited for automatic calculations on large
volumes of data.  Simplicity and speed of execution were impor-
tant.  Other criteria were that the algorithm should be directly
applicable to field-grade data, without screening or smoothing,
and that it should have sensitivity and resolution sufficient
to bring out the main features of the size distribution.

     Our criteria tended to rule out elaborate, mathematically
proper approaches such as that of Maigne5 and those based on
linear programming6 or nonlinear least squares.7  Four algorithms
were examined in detail and one of these, Twomey's nonlinear
iterative algorithm,8 was selected as the best compromise.

Twomey's Nonlinear Iterative Algorithm

     The nonlinear iterative algorithm described by Twomey8  in
1975 was intended for the calculation of the aerosol size dis-
tribution from measurements of penetration through Nuclepore
filters.  As described below, this algorithm adapted readily
to analysis of data from the Sinclair diffusion battery.

     The diffusion battery taps 1 through 11 will be designated
by the  index i.  It is convenient to define two additional taps:
Tap 0,  sampling the aerosol at the diffusion battery inlet and
tap 12, sampling the aerosol through an absolute filter.  Thus,
the data from the diffusion battery consist of a set of 13 de-
creasing aerosol concentrations C|, i=0, 12.  The last of these
is zero and is used primarily to check the zero reading of the
nucleus counter.

     Determination of the aerosol size distribution involves
comparison of the 13 observed concentrations, C^, to the corres-
ponding trial concentrations, C*.  The latter are given by the
integral expression:           1
                               106

-------
   c
ENTER
CALL PENETR TO SET UP
HISTOGRAM SIZE CLASSES
AND COMPUTE THE PENE-
TRATION MATRIX
  CALL OPTN TO ESTAB-
  LISH COMMUNICATION
  WITH THE TAPE
  READER
                                        THIS THE FIRST
                                         LINE OF A SET
                                            OF 15?
                          
-------
                     c* = N   r
                      1       o
;x)f (x)dx
          (1)
where
         N   =  the aerosol number  concentration

      f(x)   =  the (unknown) differential size distribution

         x   =  the particle diameter

             =  the fractional penetration of aerosol particles
               of diameter x through  the diffusion  battery seg-
               ments preceding  the i-th tap.  Note  that
               <}>o (x)  =1 and $! 2 (x)  = 0.
The penetration functions  i(x)  are calculated as  the product
of penetration expressions  for  each of the diffusion battery
segments  preceding the i-th  tap.   For the latter,  we use Thomas'
expression,9  which is simple and  sufficiently accurate.   Plots
of <|>j_(x)  may  be seen in reference 3 and, in an alternative form,
in Figure 4.

                      SINCLAIR DIFFUSION BATTERY AT 4.0 fipm
                                         T
                              20    30    50  70  100
                           x, PARTICLE DIAMETER, nm
200   300
            Figure 4. Penetration functions for the Sinclair diffusion battery.

                                 108

-------
     Although the algorithm  can  be  applied to the observed dif
fusion concentrations directly,  we  find that convergence  is
speeded by taking their  first  differences, D^,  which  are  the
depositions in the corresponding diffusion battery segments:


                    Di  = Ci-l  ~  Ci'   for i = 1'  12«

The corresponding trial  differences  are:

                             CO
                    D*  = N f fl (x)f(x)dx,   for  i = 1,  12.      (3)
                      i     J
                            o
where

                                               i  = 1,  12.
The functions fi^(x),  which represent the deposition  in  the  dif-
fusion battery  segments  between taps i-1 and i,  are  shown in
Figure 5.  The  function  ft12(x)  represents deposition in the
absolute filter.

     Twomey ' s algorithm  requires preselection of a number of
discrete sizes  to  represent the continuous size  distribution.
There are no fixed rules for selecting the number and spacing
of these sizes.  The  number and spacing should be such  as to
reproduce the major features of the deposition curves,  Figure
5, but using a  larger number and smaller spacing is  permissible.
The computation time, however,  increases in proportion  to the
number of discrete sizes selected.

     We commonly use  a set of eight discrete sizes,  starting
with 42.2 nm and increasing to 237  in a geometric progression
with a common ratio of 10°*2S.   Figure 5 suggests that  it might
be possible  to  add one or two larger sizes, since ft12(x) is still
changing beyond 237 nm.   However, this part of the curve is un-
certain due  to  the unknown effects  of gravitational  settling.
Furthermore, many  aerosols have relatively few particles larger
than 250 nm  diameter, which makes extension to larger sizes
unnecessary.

     In terms of the  discrete sizes, the trial depositions  are:
                           n

                     D*  =
                               . ..
                               13  3
                                109

-------
                    SINCLAIR DIFFUSION BATTERY AT 4.0 £pm
                                      CURVES 4, 5, 6, 8, 9& 10
                                      OMITTED FOR CLARITY
                       10           30

                          x, PARTICLE DIAMETER, nm
                                       100
300
             Figure 5. Deposition curves for the Sinclair diffusion battery.
where
         x.   = the j-th discrete  size

         N.   = the particle concentration at the  j-th  discrete
          -1     size
n
             = the number of discrete sizes.
     Twomey's algorithm starts  with an initial guess for the
size distribution, then refines this guess by a  series of small
changes  to  improve the fit  to  the  observed depositions.  For
the initial guess, we assume that  each of the discrete sizes
has a concentration equal to 1/n times the observed  concentration
at. tap 0; NJ  = C0/n, j = l,n.   The refined values, denoted by
N', are  obtained by applying Twomey's nonlinear  iteration
formula:
                                                                  (5)
                                110

-------
There are no  fixed  rules concerning the sequence in which the
subscripts  i  and  j  in  the formula are to be varied.  We use the
following scheme:

1.   The index  i  is varied in the sequence 1,2,3,...,12,1,2,3,...,
     l-£fj-f£f-jf • • • •

2.   At each  step of the index i, Di is computed from equation
     4 using  the most  recent values of N-;.

3.   For each i,  a  complete cycle through the index j  is per-
     formed using equation 5 to obtain refined estimates of Nj.

This procedure  is continued until there is satisfactory agreement
between D^  and  D^.

     The rationale  of  Twomey's algorithm may be seen as fallows.
Suppose, that for a particular value of i, the computed Dj^  is
smaller than  Dj_.  Equation (5), which is a sum of positive  terms,
shows that  the  only way to close the gap is to increase at  least
one of the  Nj terms.  The strategy used is to increase^all  the
Nj terms, each  in proportion to the impact it has on Di.  Similar
reasoning applies if Di is larger than D^.  By cycling  through
the subscripts  as previously indicated,Athe N-  values  are con-
tinually adjusted so as to bring each D-  closer to the  corres-
ponding D. .

     Two further  steps were taken in the computer program to
increase execution  speed:

1.   The factor ft^ in equation 5 was replaced  by 0.8 ^ij/^^max'
     where  ^imax  is the largest ftjj for the given value Of  i.
     This increases the size of the step made in each  iteration.

2.   No test  is made for convergence.  Experience has  shown that
     30 cycles  through the double loop (i = 1,12; j =  l,n)  is
     sufficient  to  achieve reasonable agreement between D*  and
     D..  Therefore, 30 cycles of iteration are used for  each
     dita set.

Computational Speed and Accuracy

     The data processing just described is done in our  Laboratory
using an IBM  360/30 computer and peripheral IBM equipment,  such
as the paper  tape reader, card punch and line printer.   The
throughput  is about four diffusion battery data sets per  minute.
The calculation  itself (the algorithm)  requires eight  seconds
per data set  and  the balance of the time is used in reading the
paper tape  and  the  printout.  This throughput is adequate for
oS? needs,  but  could probably be increased five or ten  fold by
using faster  equipment.


                                Ill

-------
     All computations are done using single-precision  IBM FORTRAN
(32 bit words).  We think that the entire procedure could also
be done with a field microcomputer programmed  in BASIC.

     A convenient check on the internal consistency of  the data
is provided by comparing the calculated concentrations, Cj,  to
the observed concentrations, C^.  With either  field or  labora-
tory data, we find that the root mean square relative  difference
between these two is usually in the range 2 to 3%, which is  be-
lieved to be comparable to the random perturbances in  the meas-
ured concentrations.  When larger relative differences occur,
they can often be traced to errors in data transmission or to
apparatus malfunctions.

     The Twomey algorithm itself has been tested with  simulated
data.  It was found that simulated data from monodisperse aero-
sols calculates to a unimodal distribution with geometric stand-
ard deviation ^1.3.  Simulated data from a mixture of  two mono-
disperse aerosols calculates to a bimodal distribution provided
that the two sizes are separated by a factor of four or more.
This resolution cannot be improved by increasing the number  of
size classes.

     The algorithm also was tested with simulated data perturbed
by random errors.  It was found that random relative errors  of
2% had little effect, but that 5% errors produced obvious dis-
tortions in the computed size distribution.  This shows that
data of good quality are required to obtain reliable size dis-
tributions.

     A more comprehensive test of the algorithm was carried  out
by analyzing real data obtained with near-monodisperse aerosols.
The body of data used in this test was obtained in a cooperative
project with personnel of the University of Minnesota  Particle
Technology Laboratory, who generated the test aerosols using
their electrical aerosol generator.  The two separate  sessions
of this project are described in references 1 and 10.

     Twenty-one of  the sets of diffusion battery penetration
readings  from  the cooperative project were analyzed by means
of the Twomey  algorithm.  These data sets include several for
which the Pollak counter, General Electric counter, or  an elec-
trical aerosol detector was used to measure diffusion  battery
penetration.

     The  results of  those tests for which the  Sinclair  nucleus
counter was used as  the detector are summarized in Table 3.
It is seen that the  geometric mean particle diameter extracted
by the algorithm agrees well with the size expected from the
electrical aerosol generator.  The geometric standard  deviations
are larger than expected, but this is a measure of the limited
                               112

-------
   TABLE 3.  RESULTS  OF  TWOMEY CALCULATION APPLIED TO DATA FROM
                 NEAR-MONODISPERSE  Nad AEROSOLS

Test
No.
2
3A
14 + 15
17
19A
19B
Aerosol
Size From
BAG (nm)
42
42
42
75
24
24
Calculated
"Old" CFC Calibration
dg (nm)
36
47
49
80
23
24
°g
1.67
1.27
1.43
1.48
1.41
1.38
fit (%)
6.6
10.2
17.2
2.3
4.9
2.6
Results


"New" CFC Calibration
d (nm)
31
43
46
85
25
25
°g
1.49
1.11
1.27
1.35
1.18
1.20
fit (%)
12.2
10.3
5.0
3.6
18.3
8.0
 CFC:   Continuous flow condensation nucleus  counter (Sinclair
       nucleus counter)

 EAG:   Electrical aerosol generator

  d :   Geometric mean diameter
   9
  a :   Geometric standard deviation

 Fit:   Root mean square relative difference  between the observed
       and trial values of aerosol concentration at the diffusion
       battery taps.


resolution of the algorithm.  The table also lists results ob-
tained using two calibration  curves for the  nucleus counter.
Although the curves were somewhat different, the calculated
particle size is nearly the same.

OVERALL SYSTEM:  SERVICE AND  MAINTENANCE

     A block diagram of the complete aerosol measurement system
is shown in Figure 6, while a photograph showing the system  in-
stalled in a roof-top air sampling station is shown in Figure 7.
                         "
    -SBJ sDs-s- aus
                             113

-------
                               ROTARY
                               15-PORT VALVE
AEROSOL
IN
         4 Cprn  J U
                 SINCLAIR
                 DIFFUSION
                 BATTERY
                    4 gpmTO OTHER
                    INSTRUMENTS
            60 £
            BALLAST
            TANK
                                            SINCLAIR
                                            NUCLEUS
                                            COUNTER
                                    STEP AND
                                    HOME
                                    SIGNALS
                                     CONVERT
                                     SIGNAL
                                                          TO PUMP
                              TIMING AND
                              CONTROL
                              CIRCUIT
                                           ANALOG TO
                                           DIGITAL
                                           CONVERTER
              Figure 6. Block diagram of aerosol measurement system.

tank  is  that  some modification of the size distribution is in-
curred by  losses  and by coagulation.  We have estimated mathe-
matically  that  losses by diffusion do not change  the size dis-
tribution  significantly, but coagulation (assuming  a typical
urban aerosol concentration at the ballast tank  inlet)  causes
a 40% reduction in  the concentration of 5 nm particles.  For
particles  larger  than 10 nm, the loss (or gain)  is  insignificant.

Routine  Service Schedule

     When  the system is in use for hourly sampling  of the outdoor
aerosol, it is  serviced once each weekday.  On weekends,  the
system operates unattended for 72 hours.  Our recent experience
indicates  that  in cool or  cold weather, the service interval
could be extended to one week.

     The parameters which  are checked during each visit are the
temperature in  the  nucleus counter cold tube and  the alcohol
supply and flow rate.   Other parameters, such as  the nucleus
counter  lamp  intensity and the aerosol flow rate  have been found
to be very stable.   The cycle initiation time is  also checked
each visit and  has  been found to be reliable.  The  punched tape
is removed twice  a  week to avoid handling awkwardly long  tapes,
but this interval could be extended to one week  if  desired.
                                114

-------
Maintenance

     A provisional  maintenance schedule has been established
for the Sinclair  diffusion battery and nucleus counter in which
the apparatus  is  disassembled and thoroughly inspected at ap-
proximate  1000  hour intervals of running time.  Particular areas
of concern  in  the inspection are the diffusion battery segments,
the rotary  valve  seals and the lenses in the nucleus counter.
The segments should be inspected for discoloration or debris
on the upstream surfaces.   (A slight accumulation of debris is
usually found  on  the first segment.)   The segments should be
inspected  for  blocked holes by holding them up to a strong light.

     If required, the diffusion battery segments are cleaned
by soaking  in  ethanol, acetone or a 20% solution of phosphoric
acid.  The  solvent  treatment should not exceed one hour,  since
the solvents may  attack the aluminum and epoxy used to mount
the segments.   The  organic solvents are cleared from the  segments
by drawing  air  through them.

     The rate  of  fouling of the diffusion battery segments is
very low due to the low duty cycle used.  In the normal one cycle
per hour schedule,  there is flow through the diffusion battery
only 7.2 minutes  per hour.  The segments between taps 10  and
11, where  the  greatest mass deposition is expected, have  a duty
cycle of 1  minute per hour.  The nucleus counter is to a  large
extent self-cleaning due to the continuous flow and condensa-
tion of alcohol in  the cold tube.

     Upon  reassembly of the system,  or after any move of  the
system, it  is  advisable to check for  leaks.   One convenient check
is to place an  absolute filter at the diffusion battery inlet,
then go through a normal measurement  cycle.   Leaks which  con-
tribute 200 to  300  particles/cm3 are  detectable in this way.

USE HISTORY AND FUTURE WORK

     Three  extended sampling sessions have been conducted to
date with  the  Sinclair diffusion battery and nucleus counter.
The first  of these  was in  August 1976, on the roof of the dormi-
tory at New York  University Medical  Center using an earlier ver-
sion of the apparatus.  Data transcription was done by hand and
233 hours  of data were obtained.  The results of this work,  which
was part of a  multi-laboratory study  of the  New York aerosol
under summer conditions, will be described in a forthcoming
article.2

     The second and third  sampling sessions  were conducted on
the roof at EML during November 1977,  and February 1978   The
full complement of  equipment, as described in this report,  was
used   The  two  sessions resulted in  966 hours of data. At this
writing  all these  data have been reduced to cards and a  few
statistical summaries have been done.

                                116

-------
Figure 7. Sine/air diffusion battery and nucleus counter mounted in
         the rooftop sampling station.  (The rotary multiport valve
         is shown in the foreground and the nucleus counter is in
         the left background. Note that the screen battery, rather
         than the CHS or HS battery, is shown in this photograph).
                              115

-------
     Figure  8  shows the grand average number-weighted aerosol
size distribution based on 400 measurements made on the roof
at EML during  November and December 1977.  The distribution is
seen to  be unimodal,  with the modal diameter at 30 nm.  The curve
has a bell shape  closely resembling that of a log-normal distri-
bution.  The grand average number concentration was 26,900 cnT3.

     Figure  9  shows the average diurnal pattern of concentration
for 42 nm particles.   It is seen that the minimum and maximum
concentrations occur  in the predawn hours and during the morning
rush hours,  respectively.  A second maximum occurred during the
afternoon rush hours.   This latter maximum was not present in
the earlier  data  taken during the summer.2

     Additional sampling sessions are planned and further appara-
tus modifications are contemplated to make the system more con-
venient  to use.  We anticipate that in the near future a second
system will  become available so that sampling can be done simul-
taneously at two  sites.

     The most  recent  sampling session also indicated a need for
further  development or calibration work with the  nucleus counter.
This sampling  was done during extremely cold weather.   The con-
centrations  measured  with the nucleus counter were abnormally
low, possibly  due to  the reduced amount of alcohol vapor available
to condense  on particles.  We therefore plan to check  the nucleus
counter  calibration over a wide range of temperatures  in a labora-
tory environmental chamber.

SUMMARY

     The Sinclair diffusion battery and nucleus counter  have
been improved  and modified to make them suitable  for  extended
use in uncontrolled environments.   A new sequencing  valve,  com-
patible  with digital  data recording circuitry and  the  require-
ments of aerosol  mechanics, has been designed and  constructed.
An accurate  timing and control circuit and a data  recording  de-
vice have been added  to make up a system which operates  unat-
tended for three  days  or more.

     Data processing  techniques have been developed  to conven-
iently handle  data from the diffusion battery and  nucleus coun-
ter   The processing  is largely automatic and results  in a com-
puter card file of differential size distribution  data.

     Over 1000 hourly  measurements of the urban aerosol  in New
York City have been made with the  system.   Operation  in  winter
months has been found  to be virtually trouble free.  Operation
Tn hot,  humid  weather  is more difficult,  but it is anticipated
that the recent modification will  prove to be adequate for sam-
pling planned  for this summer.


                                117

-------
                      501
                      40 I
                                  AVERAGE TOTAL CONCENTRATION

                                  = 26,900/cm3
oo
                  CO

                  u
                  -ft
                  •o

                  5
                  vt

                  o
                   a.
                  •o
                   o

                   O)
                  _o
301
2Q\
                      10
                                                  AVERAGE SIZE DISTRIBUTION BASED

                                                  ON 400 HOURLY READINGS
                                         10              30

                                                PARTICLE DIAMETER, nm
                                                   100
300
                               Figure 8. Average number-weighted size distribution on EML roof,

                                       November-December,  1977.

-------
     601—
     50
CO
 3
 o
     40
     30

     20
     10
                                          AVERAGE DIURNAL PATTERN

                                          FOR 42 nm PARTICLES, BASED

                                          ON 17 DAYS OF DATA
     Ol I   I  I  I  I  I  I   i  I  I
            I   I  I  I  I  I  I  I
I  I  I  I
      MID
6 AM         NOON         6 PM

        LOCAL STANDARD TIME
       MID
    Figure 9. Average diurnal pattern for 42 nm particles on EML roof.
                                 119

-------
ACKNOWLEDGEMENT
     F. Guggenheim and M. Cassidy, both of EML's  Instrumentation
Division, contributed the design and supervised the construction
of the multiport rotary valve and the timing and  control  circuit,
respectively.

REFERENCES

 1.  Sinclair, D., R.J. Countess, B.Y.H. Liu, and D-Y.H.  Pui.
     Automatic Analysis of Submicron Aerosols.  In:  Aerosol
     Measurement. Proc. of Aerosol Measurement Workshop,  March
     24-26, 1976, to be published by University of Florida  Press,
     1978.

 2.  Knutson, E.O., D. Sinclair, and B. Leaderer.  New York Sum-
     mer Aerosol Study — Number Concentration and Size Distri-
     bution.  New York Academy of Sciences, to be published,
     1978.

 3.  Sinclair, D.  A Portable Diffusion Battery - Its Application
     to Measuring Aerosol Size Characteristics.   J. Am. Ind.
     Hyg. Assoc.  33:729-735, 1972.

 4.  Sinclair, D., and G.S. Hoopes.  A Continuous Flow Condensa-
     tion Nucleus Counter.  J. Aerosol Sci. 6:1-7, 1975.

 5.  Maigne, J.P., P.-Y. Turpin, G. Madelaine, and J. Bricard.
     Nouvelle Methode de Determination de la Granulometrie  d' un
     Aerosol au Moyen d'une Battery de Diffusion.  [New Method
     for Determination of the Granulometry of an  Aerosol  by Means
     of a Diffusion Battery.]  J. Aerosol Sci. 5:339-355, 1974.

 6.  Cooper, D.W., and L.A. Spielman.  Data Inversion Using Non-
     linear Programming with Physical Constraints:  Aerosol Size
     Distribution Measurement by Impactors.  Atmos. Environ.
     10:723-729,  1976.

 7.  Mallove, E.F., and W.C. Hinds.  Aerosol Measurement  by Com-
     bined Light Scattering and Centrifugation.   J. Aerosol Sci.
     7:409-423, 1976.

 8.  Twomey, S.  Comparison of Constrained Linear Inversion and
     an Iterative Nonlinear Algorithm Applied to  the Indirect
     Estimation of Particle Size Distributions.   J. Comput  Phys
     18:188-200, 1975.

 9.  Thomas, J.W.  Particle Loss in Sampling Conduits.  in:  IAEA
     Symposium Proc.  Vienna, 1967.  pp. 701-712.

10.  Sinclair, D., R.J. Countess, B.Y.H. Liu, and D.Y.H.  Pui.
     Experimental Verification of Diffusion Battery Theory.
     J. Air Pollut. Control Assoc. 26:661-663, 1976.
                               120

-------
                             PAPER 6


        SELECTING LABORATORY METHODS FOR PARTICLE  SIZING
                          RONALD G.  DRAFTZ
                 FINE  PARTICLES RESEARCH LABORATORY
        ILLINOIS INSTITUTE OF TECHNOLOGY RESEARCH INSTITUTE
ABSTRACT

     In spite of  continuing efforts to develop in-situ particle
sizing methods  for  process streams, there still remain many  in-
stances when  in-lab particle sizing is necessary or  desirable.
The analyst has many methods available for  particle  sizing and
often faces the choice  of which one is best.

     This paper presented some general guidelines for selecting
a particle sizing method  based on sample  size,  instrument size
range, analysis time, and measurement parameter and  principle.
Suggestions were  given  for sample preparation  and microscopical
methods for previewing  samples to select  the  ideal sizing method,
                                121

-------
                             PAPER 7
             LONG TERM FIELD,EVALUATION OF CONTINUOUS
                       PARTICULATE MONITORS
                            A. W. GNYP
                          S. J. W. PRICE
                         C. C. ST. PIERRE
                            D.  S.  SMITH
                   INDUSTRIAL  RESEARCH INSTITUTE
                      UNIVERSITY OF WINDSOR
ABSTRACT
     A critical field evaluation of five different particulate
monitors representing four distinctly different principles of
operation was carried out over a one year period at a secondary
lead smelter.  Instrument performance was rated on the basis
of accuracy, reliability and maintenance as criterion variables.

     The Lear Siegler RM41 and RAC transmissometer responses
were primarily dependent on particle size when aerodynamic diam-
eters exceeded 1 ym.  Improvements in the long-term reliability
of the Environmental Systems Corporation PILLS V backscattering
device could make it potentially more useful than the best trans-
missometer because its calibration appears to be less sensitive
to changes in particle size, color and refractive index.  The
Research Appliance Company transmissometer was adequate for moni-
toring emissions from the controlled reverberatory mode of opera-
tion but did not appear to be capable of detecting large par-
ticles whose diameters exceeded 25 pm during lead alloying kettle
production.  Very limited potential for application to either
the reverberatory or lead alloying kettle modes of operation
was exhibited by the charge transfer IKOR 2710 particulate moni-
tor.  Because of repeated mechanical failures in the sampling
module of the Research Appliance Company beta radiation attenuat-
ing device supplied for the study, it was impossible to criti-
cally evaluate its monitoring capabilities.

     Reliable continuous monitoring is possible in stacks ex-
hausting gases that have passed through efficient control equip-
ment and contain particulate matter having constant physical
and chemical properties over long time periods.  Continuous par-
ticulate monitors offer interesting possibilities for improving

                              122

-------
surveillance  capabilities,  validating manual compliance testing
and minimizing  emissions from industrial sources on a 24-hour
real-time basis.

INTRODUCTION

     Increasing awareness of the potential dangers arising  from
the discharge of  toxic materials into the environment from  indus-
trial sources has prompted  regulatory agencies to establish maxi-
mum emission  levels.   At the present time compliance is deter-
mined by periodic manual source testing programs that can provide
data that are valid,  at best, only for the short-term testing
periods.  Conventional manual stack sampling methods cannot pro-
vide records  of any periodic excessive emissions resulting  from
faulty operation  of installed abatement equipment or process
upsets.

     Assurance  of long-term compliance with and enforcement of
regulations requires  the availability of reliable continuous mon-
itoring capabilities.   Although there are several promising par-
ticulate monitoring systems, their application has been restricted
by the lack of  information  on their accuracy,  precision and long-
term reliability.  In the absence of such data,  it is not sur-
prising that  industries have been reluctant to commit significant
capital outlays for the installation of large  scale continuous
monitoring systems.

     This study concentrated on the evaluation of the perfor-
mance characteristics of continuous particulate  monitoring de-
vices because,  with the exception of transmissometer systems,
there are no  established performance specifications for  any com-
mercially available monitors.  The principal objectives  of  this
investigation were to assess the suitability,  reliability, and
accuracy of continuous particulate monitors for  stationary  sources
on the basis  of field experience at a secondary  lead smelter.

Site

     The secondary lead processing plant selected for this  study
provided an opportunity for assessing the viability of  using
continuous instrumentation  for  real-time monitoring of  lead,
which had been  designated as a  hazardous pollutant by Environment
Canada.  From a practical viewpoint,  the stack was of suitable
size and construction to simultaneously accommodate five con-
tinuous monitors  and  three  manual sampling trains.   The two
distinctly different  operating  modes:

       i.  uncontrolled lead alloying kettle

      ii.  baghouse equipped reverberatory furnace

provided a wider  range of emission characteristics than normally
obtainable from a time invariant process.

                                123

-------
Process Exhaust System

     Reverberatory furnace gases, exhausted by means of  an  18,000
scfm fan, were cleaned in a baghouse before entering the stack
through horizontal breeching at the 55-foot level as illustrated
in Figure 1.  Gas temperatures to the bags were kept below  300°F
by means of ambient air drawn through the intakes in the ducting
from the reverberatory furnace.  Cleaning of the baghouse was
initiated manually at 15-20 minute intervals.  Mechanical shaking
of the bags in each of the three baghouse compartments for  periods
of 25-30 seconds set up well-defined vibrations in  the stack.
Pulses of particulate emissions were detected by all of  the con-
tinuous monitors during bag cleaning.

     Emissions from the lead alloying kettles by-passed  the bag-
house.  They were removed from the top of the kettles by fume
hoods located at the rear of each unit.  These fume hoods were
connected to a common 30-inch, round, duct which led to  a 24,000
scfm fan located at the base of the stack.  During  reverberatory
furnace processing both the baghouse and alloying kettle fans
were operational; otherwise the baghouse fan was not used.

     The test plant had several kettle units.  They were used
for remelting, alloying and refining purposes.  Each consisted
essentially of a hemispherical cast steel bowl mounted over
burners fired with light industrial oil.

Instrument Selection

     Instruments commercially available in Canada at the incep-
tion of this investigation were limited to systems  employing

        i.  light attenuation

      ii.  light scattering

     iii.  charge transfer

      iv.  beta-radiation attenuation.

Instrument selection was dependent, partly, on the  cooperation
of American and Canadian manufacturers and distributors. As
a result, the final complement consisted of the five monitors
listed  in Table 1.

TESTING PROGRAM

     Figure 2 illustrates the relative locations of the  twelve
ports,  installed at the enclosed sampling and exposed  instrument
platforms, with respect to the breeching from the baghouse.
                               124

-------
 STACK
xxxxx
SAMPLING LEVEL
                 INSTRUMENT LEVEL
                          DILUTION
                          AIR
                      EXHAUST FROM
                      REVERB FURNACE
                                      OVERHEAD
                                      FLUE
                   EXHAUST FROM
                   KETTLES
                     REVERBATORY
                     FURNACE
                                             o
                                             o
                                     KETTLES
                                 O
                                 o
                            o
                            o
      Figure 1. Plan and elevation of secondary lead smelter.
                       125

-------
                                                      EL 96' 0"
  SAMPLING
  PLATFORM
 EL 75' 3"
 EL 74' 9"
 EL 74' 3"-
 EL 73' 9'"
EL 70' 9"
/
                                  //
                                                                EL 82' 4"
                                                                EL 81' 10"
                                                                -EL 81'4"
                                                                EL 80' 10"
                                              EL 77' 3"
                                            INSTRUMENT
                                            PLATFORM
          Figure 2. Elevations of ports and instrument and sampling levels.
                                  126

-------
        TABLE 1.  CONTINUOUS  PARTICULATE  MONITORS  SUBJECTED
                        TO FIELD EVALUATIONS
                       1	—	
  Principle of         Instrument
     operation	model	Manufacturer

Light  Attenuation   RM 41 No. 275     Lear Siegler Inc.
                                       Environmental Technology
                                       Div.

                     RAC No. 2700      Contraves Goertz Corp.
                                                with
                                       Research Appliance Co.

Light  Scattering    PILLS V           Environmental Systems
                                       Corp.

Charge Transfer     2710              IKOR Incorporated

Beta Radiation      Automatic Stack   Research Appliance Co.
Attenuation         Monitor No. 2412
Sampling  Trains

     The  basic components of  the  particulate matter sampling
trains, distributed by the Western  Precipitation Division of
Joy Manufacturing  and sold under  the  trade  name "Emission Param-
eter Analyzer",  are represented schematically  in Figure 3.  Prior
to use  the  S-type  pitot tube,  orifice rate  meter and dry total
gas meter were calibrated in  the  University of Windsor labora-
tories  according to EPS standard  procedures.1

     Aerodynamic particle size determinations  were carried out
by means  of an Andersen Stack  Sampler in  conjunction with a
second  Joy  sampling train. The standard  sampling probe-pitot
tube arrangement was modified  by  extending  the S-type pitot tube
in order  that velocity determinations could be made in the vi-
cinity  of the sampling nozzle.  Figure 4  shows the arrangement
of the  extended  S-type pitot  tube,  Andersen impactor and sampling
nozzle.

     In order to acquire samples  for  microscopic particle sizing
and to  test the  validity of single  point  monitoring and sample
acquisition a third sampling  train  was required.  The arrange-
ment of components, illustrated  in  Figure 5, also facilitated
the acquisition  of gas samples for  on-site  gas chromatographic
analysis.

Location  of Ports

     Because seven ports were required for  the five particulate
monitors  and four  ports were  needed for the manual sampling
                               127

-------
                         TEMPERATURE SENSORS
                                   FILTER
                  HEATED AREA   // HOLDER
                   THERMOMETER
    PROBE
   S - TYPE
   PITOT TUBE
               STACK
               WALL
                  PITOT  L
                MANOMETER
                THERMOMETERS


                  ORIFICE
         BYPASS VALVE GAUGE
                               DRY
                            I   TEST
                            V  METER
                  AIR-TIGHT
                  PUMP
\ ___ /_^f^ _____ |
THERMOCOUPLE |~
              l_
                                CHECK
                                VALVE
                                  VACUUM
                                  LINE
                   Figure 3. Paniculate matter sampling train.
                                 128

-------
                    NOZZLE
S-TYPE
PITOT TUBE
                       ANDERSEN
                       CASCADE
                       IMPACTOR
         THERMOCOUPLE
                        PROBE
                        SHEATH
Figure 4. Arrangement of extended S-type pitot tube with respect
        to Andersen cascade impactor and sampling nozzle.
                          129

-------
                  MERCURY
                  BAROMETER
DRY GAS
METER
GAS SAMPLE
BULB
                                                      VACUUM PUMP
                 Figure 5. Components of membrane sampling train.
trains, it was not possible to locate all of them at  one  level
on the stack.  Limitations imposed by scaffolding dimensions
and minimum requirements of the EPS source testing  code1  dictated
that the manual sampling train ports be provided at the upper
level as shown in Figure 2.  The arrangement of the continuous
monitoring instruments is shown in Figure 6.  Under the test
conditions all monitors were at least four stack diameters  down-
stream from the flow disturbance created by the baghouse  breech-
ing.  The manual sampling trains were 6 1/2 stack diameters from
the same flow disturbance and 3 1/2 diameters upstream  from the
stack exit.

     The placement of the instruments at the lower  level  was
designed to minimize mutual interference.  The proximity  to the
flow disturbance was not expected to handicap the sampling  pro-
gram because submicron particulate matter would predominate
during the reverberatory furnace campaign.  Introduction  of
exhaust gases at the base of the stack during the lead  alloying
kettle production mode provided more than 8 stack diameters of
separation between the sampling sites and the exit  from the
induced draft fan.

Sampling Points

     All particulate matter loading evaluations were  determined
from samples collected at 12 points along each of the two per-
pendicular traverses as shown in Figure 7.

     Aerodynamic particle size determinations with  the  Andersen
in-stack cascade sampler demand that isokinetic conditions be
maintained at the nozzle for representative sample  collection.
                               130

-------
                                            PILLS V
                         BAGHOUSE    _
               D
                                                      RAC
                                                      "RETRO-
MEMBRANE
TRAIN
                     NOT USED
                          BREECHING
                                                       LEAR SIEGLER
                                                       "RETRO"
            STACK
            DIAMETER = 45 FT
  ELEVATIONS
    O  81' 10"
    A  82' 4"
    O  8T 4"
    D  80' 10"
ALL PORTS CAPPED
WHEN NOT IN USE
           SAMPLING PLATFORM
                                                                            N
                                                 INSTRUMENT PLATFORM
             Figure 6. Arrangement of ports at the sampling and instrument levels.

-------
                         SAMPLING PORT
                         FOR MEMBRANE FILTER
             SAMPLING
             PORTS
  TRAIN

PARTICULATE O
PARTICLE SIZE 9
MEMBRANE •
                  Figure 7.  Location of sampling points.


 In  addition,  a  constant  volumetric flow rate must be maintained
 through  the device  because the impaction efficiency of each  col-
 lecting  plate is  a  function of the gas flow rate.  In order  to
 satisfy  both  conditions, it was necessary to locate sampling
 points along  both traverses where the stack conditions were  such
 that  a constant flow rate provided, essentially, isokinetic
 sampling conditions.   Aerodynamic particle size sampling was
 carried  out at  the  points shown in Figure 7.  The cumulative
 method of  sample  collection was employed for both particulate
 loading  and particle size determinations.

      Initially, the  membrane sampling train was to be used to
collect  particulate  matter for  microscopic particle sizing and
gas samples for chromatographic analyses.  In view of its limited
traversing capabilities  this train provided samples from a single
fixed point only.  Because two of the continuous particulate
                                132

-------
monitors represented  stack  conditions  in  terms  of  measurements
at a single point,  it was  useful  to  check  the validity  of  their
data with grain  loading  determinations derived  from  single point
sample acquisition  with  the membrane train.  The sampling  probe
on this train  provided sample  collection  from the  point £2 in
Figure 7.                                          r      ^

Sampling Time  Per  Point  and Gas Sample Volume

     Sampling  times per  point  for particulate loading and  particle
size determinations were designed to provide readily measurable
amounts of materials  without overloading  the filter  or  plates
of the Andersen  impactor.   Consequently,  gas sample  volumes cor-
responded to  about  150 ft3  for particulate matter  and approxi-
mately 125 ft   for  particle sizing tests.   The  membrane train
was kept at one  point for  the  duration of  any test.

CONTINUOUS PARTICULATE MONITOR DATA  LOGGING

     Although  all  the continuous  particulate monitors were in-
stalled at the lower  level, where they were exposed  to  adverse
effects of the environment, the remote control  and recording
components had to  be located in a protected area equivalent to
an industrial  control room.  The  sampling  level was  modified
to control room  specifications when  it became apparent  that
location of  the  remote control and recording devices in the field
office, at ground  level, would not permit  real  time  observation
of monitor performance in conjunction  with the  manual sampling
program.  Before and after every  test, each continuous  particu-
late monitor  system was zeroed and calibrated according to pro-
cedures outlined by the instrument manufacturers.

Optical Transmissometry

     The electrical output from the  optical head assembly  of
the RAC transmissometer passed to the  remote control panel which
provided:

        i.  direct  readings for 0-100%  opacity

       ii.   the operating mode selector switch  (normal,  span and
            zero calibration modes)

     iii    electrical connections for  both the  data  transmitting
           cable and 115-volt single-phase power  input.

The two-speed  strip chart recorder provided with the remote con-
trol panel was not  used because its  scale  was inadequate for
the scientific purposes of this study.  Instead, the remote out-
put signal was fe^to a Hewlett-Packard, Model  7100B, strip chart
Recorder with  a  17500 A multiple-span  input module.


                                133

-------
     In the Lear Siegler RM 41 monitor, the electrical  signal
from the transducer unit was directed to the Optical Density/
Opacity Converter which provided, simultaneously, linear opacity
and optical density outputs.  The convertor unit also provided

       i.  manual controls for remote zero and span calibration
           checks

      ii.  a remote fault indicator for the transmissometer

     iii.  a shutter position indicator

      iv.  an over-range indicator for the selected measurement
           range

       v.  a filter air-purge flow restriction indicator

      vi.  an automatic compensation for zero drift and exces-
           sive compensation indicator

     vii.  an alarm level indicator and reset switches.

     The four-inch strip chart recorder normally supplied with
the RM 41 system as an optional unit was replaced with a Hewlett-
Packard Model 7100B version, equipped with a 17500 A multiple-
span input module, for improved accuracy when integrating optical
density signals.

Backscattering

     The ESC Particulate Mass Concentration Monitor was a com-
pletely self-contained unit with meter read-out and range selec-
tion located on the instrument panel at the monitoring level.
For remote data logging at the sampling level control room, the
output signal was fed to a Rikadenki B-161-361 Series multipen
recorder with a 50 ohm resistor connected across its input ter-
minals.  The resulting 0-1 volt analog signal was integrated
with a Monitor Lab Model 8640 Mean-Value Integrator.  A second
channel of the Rikadenki recorder produced a permanent record
of the output from this integrator.  On the model supplied for
this investigation the manufacturer provided measurement ranges
of 0.05, 0.2, 1.0 and 5.0 gr/acf.

Charge Transfer

     The continuous output signal from the IKOR 2710 sensor probe
was fed to a control unit consisting of

       i.  a power supply for the device

      ii.  a sensor output display
                               134

-------
     iii.  an integrating totalizer

      iv.  a test set function switch that  is used for checking
           sensor electronics.

The 0-10 volt output was fed to one of the  Hewlett-Packard Model
7100B recorders located in the control room area.  Five decades,
varying from 0.1 to 1,000, provided sensitivity selection for
mass flow sensing.

Beta Radiation Attenuation

     The RAC Automatic Stack Monitor control console  in associa-
tion with a Monroe, Model 1810, programmable printing calculator
regulated the entire operation of this system.  Automatic gov-
erning of all system sequences, as well as  individual component
functions, was performed by the master control module.  Input
signals from the instrument subsystems were assimilated by the
control module and then transmitted to the  mini-computer for
storage, calculation and printout.

     The control console panel provided visual, digital readouts
of

       i.  gas sample volumes

      ii.  beta counts for filter taring and loading

     iii.  time intervals

Tape printouts of the above parameters and  particulate matter
concentrations in appropriate units were obtained from the mini-
computer .

RESULTS

     Thirty-two particulate matter concentration, particle sizing,
and membrane tests were carried out at the  secondary  lead smelter
during the nine month period from 4 June, 1976 to 7 March, 1977.
Twelve of these tests accounted for the reverberatory furnace
mode of operation.  The remaining tests were conducted while
refining processes were in progress in the  various lead alloying
kettles.

     The simultaneous evaluation of the five continuous particu-
late monitors ended on 15 October, 1976 after the completion
of seventeen tests.  A five month period of long-term reliability
evaluations terminated on 7 March, 1977.
                               135

-------
Particulate Matter Concentrations

     Since particulate concentrations in the stack gases were
determined simultaneously with three different trains, it  is
possible to compare single point  (membrane) and limited travers-
ing  (Andersen impactor) sample acquisition with the standard
EPS  source testing procedures.

     Figure 8 illustrates the close agreement between the  data
obtained from the 24 point conventional grain loading tests and
values based on particle size determinations using 12 sampling
points.  During some of the lead  alloying kettle tests, a  wide
range of particulate loadings in  the stack gases was obtained
through the cooperation of the Smelter Supervisor, who provided
conditions simulating  undesirable upset episodes that could occur
during normal processing.

     With the exception of two tests during which obvious  sam-
pling train failure occurred as a result of glass breakage, a
paired t-statistic test indicates a 92% level of confidence for
the  particulate concentrations measured.

     According to Figure 9, particulate concentrations determined
from the one point, membrane, sample acquisition technique are
approximately 35% higher than the mean values determined from
the  24 point and 12 point traversing tests.  Deviations of this
magnitude indicate that single point sampling with membrane
filters can serve only as a semi-quantitative measure of con-
tinuous particulate monitor performance.   It should be noted
that the mode of plant operation  did not significantly bias the
particulate concentrations measured with the membrane filter.

Aerodynamic Particle Size Distribution Data

     The experimental  data were plotted on logarithmic-probability
(log-prob) paper as illustrated by Figure  10.  Normal heating
of a molten charge during lead alloying kettle processing  pro-
duced particulate emissions corresponding  to the linear plot
exemplified by Test 24.

     Disturbance of a  kettle melt by the addition of  sawdust
or sulfur was conducive to the generation  of particles whose
cumulative log-probability size distribution plot showed two
linear segments comparable to the Test 13  representation in Fig-
ure  10.  The break in  the linearity seems  to be  indicative of
particulate production as a result of normal emissions from a
hot  melt plus charring of granular additives dumped on to  the
hot  metal surface.
                               136

-------
    20
Z .a

_i <5



11
GO fl

Z <
01 CC

£z
111 HI
0 O
Z Z
< O
  O
    16
i:   12
            BEST LINEAR FIT


            95% CONFIDENCE
                            CYCLONE FAILURE
                           8
                                       12
16
20
                   PARTICULATE SAMPLING TRAIN

                   CONCENTRATION, arbitrary units




  Figure 8.  Comparison of standard and particle sizing train data.
                           137

-------
      20
      16
  5   12
03
  O
  U
          BEST LINEAR FIT 	

     PERFECT AGREEMENT	


95% CONFIDENCE INTERVAL H!
                             8
                             12
16
                                                            20
                        MEAN CONCENTRATION OF
                      SAMPLING TRAINS, arbitrary units


Figure 9.  Comparison of paniculate concentration determinations from

         single point membrane and two traversing techniques.
                             138

-------
E
a.
LU


<

Q

O
Q
O
cc
HI
      50

      40

      30


      20
      10

      8
       1

     0.8


     0.6



     0.4





     0.2
1
—


—


—
—

—

_




•—
1
1 . I 1 1 1 , 1 , , , 1 , , 1,
RUN 13 - KETTLE / , |
WITH ARTIFICIALLY ' ' /
CREATED PEAK LOADS / / i
\ / i -
\ / / '
\ / °
V / RUN 24 - /
9 o KETTLE i
/ // '
/ ° / f
1 r i
/ /
? ' J\
1 D ^\
f ; y\
1 n f RUN 20 -
I / / REVERBERATORY
^\ i f
Y J( 4 FURNACE
/ ? /
1 / /
' /
/
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
1
—


—


—
—

	

_




•—
|
        0.1      125  10     30   50    70      90        99     99.9


        PERCENT LESS THAN OR EQUAL TO STATED SIZE ON A MASS BASIS



       Figure 10.   Typical aerodynamic particle size distribution data.
                                 139

-------
     Test 20 illustrates the typical log-probability distribu-
tion of the particles collected during the reverberatory  furnace
mode of operation.  The two linear portions of the resultant
plot again suggest that the sample was a composite of emissions
from two different processes.  It must be remembered that during
reverberatory furnace production the lead alloying kettles were
normally operational.  As a result, reverberatory furnace test
samples really represent superimposition of baghouse emissions
on conventional kettle particulate matter.  When the data from
Test 15 are excluded, on the basis of sample color and documenta-
tion of simultaneous lead-alloying kettle operation, from the
eleven other reverberatory tests, the arithmetic mean of  the
aerodynamic particle diameters of the baghouse emissions  is 0.43
ym with a standard deviation of 0.13 ym.  The arithmetic mean
of the aerodynamic particle diameters for the twenty lead alloy-
ing kettle tests  is 18.9 ym for the approximate range from 0.05
to 150 ym.

Particulate Matter Analysis

     Identification of the major metallic components in the par-
ticulate emissions was required in order to determine whether
continuous monitor performance characteristics could be related
to particle compositions.  A preliminary ESCA determination
showed that lead, tin and zinc were the three principal metals
in both the reverberatory furnace and lead alloying kettle stack
emissions.  No other metals were present, consistently, in excess
of 0.5%.

     The results  of X-ray fluorescence analyses carried out in
the EPA laboratories at Research Triangle Park, North Carolina,
confirmed that lead, tin and zinc would be the predominant metal-
lic species in all the samples.

     Due to the presence of tin oxides in the collected solid
materials, it was necessary to fuse the particulate matter before
atomic absorption analyses were carried out on all samples.
The data in Table 2 represent average values determined from
the combination of particulate matter recovered from the  nozzle,
probe, cyclone, filter and impinger components of the sampling
train.

Continuous Particulate Monitor Performance

     Figure 11 illustrates the Lear Siegler RM 41 instrument
response.  It is  impossible to correlate the results of the 32
tests by a single curve.  However, three distinctly different
least square linear calibration plots can be recognized in terms
of the aerodynamic particle size of the emissions.  The behavior
of the RAC instrument was essentially similar to the Lear Siegler
RM 41 as shown in Figure 12.
                               140

-------
TABLE 2.  CHARACTERISTIC COLORS AND COMPOSITIONS
             OF PARTICULATE SAMPLES

Test
number
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
Color of particulate
on membranes
grey
blue
grey



grey
dark


grey

brown
black
brown

grey
black
brownish grey
white
grey
white



black
black

black
brownish





dirty
grey

membranes
black
brown
brown
whitish
grey
white
dark
ruined



grey
yellowish
yellowish
grey
grey

dark
brownish
black


black
silver grey
dark

grey
brown
grey
black
light grey

black
brown

Composition
by atomic
Pb
11
31
27
6.0
22
11
30
27
50
39
44
14
45
32
47
36
11
23
24
16
12
9.6
22
56
58
40
39
Sn
4
22
18
3.
21
6.
12
4.
5.
6.
5.
5.
7.
5.
15
14
3.
30
31
33
11
9.
20
8.
8.
3.
3.
of particulate matter
absorption analysis ,
weight %




5

7

3
8
9
6
1
0
9


6




4

6
7
0
6
Zn
0.
2.
2.
0.
*
•
•
12
1.
0.
*
3.
0.
.
•
2.
0 .
2.
2.
1.
2.
1.
2.
0.
•
•
•

33
0
6
23
39
95
95

2
28
56
3
75
70
75
5
30
1
1
9
4
5
2
11
11
13
14
Total
metal
16
55
47
10
44
18
42
43
57
46
50
22
53
38
63
52
15
56
57
51
25
20
43
65
66
43
43
                      141
                                    (continued)

-------
              TABLE 2  (continued)
Test
number


28
29
30
31
32
Color of particulate


brown light cream
membranes ruined
orange grey grey
black
black
Composition of particulate matter
by atomic absorption analysis,
weight %

Pb
28
16
19
33
34

Sn
2.9
2.4
4.2
4.6
19

Zn
0.24
.11
.21
.55
.62
Total
metal
31
18
23
38
53

  JD

  O
  •
  U)
  O.
  O
     0.08 -
     0.06 -
          BEST LINEAR FIT
          95% CONFIDENCE:?!
                INTERVAL!
     0.04 -
     0.02 -
        0        4        8        12       16       20

         SAMPLING TRAIN CONCENTRATION, arbitrary units


Figure 11.   Calibration data for Lear Siegler RM 41 transmissometer.
                         142

-------
             CO
             Q.
             .O
             o
             73
             CO
             2
             LU
             Q
             Q_
             O
                0.08 -
                0.06 -
                    95% CONFIDENCE :i?i
                         INTERVAL^
                0.04 -
                0.02 -
                   04      8      12      16      20
                    SAMPLING TRAIN CONCENTRATION, arbitrary units

                  Figure 12.  Calibration data for RAC transmissometer.

     According  to Figure  13,  it would appear that there  are  two
distinctly different  calibrations for the  PILLS V continuous
particulate monitor.   These lines correspond to periods  following
initial installation  and  extensive field servicing  by personnel
from ESC head office.

     When the 31  test points  during which  the IKOR  device  was
operational are plotted in  Figure 14, particle size considera-
tions once again  provide  a  means of classifying  instrument per-
formance according to the two linear plots.

     It was extremely difficult to derive  reliable  calibration
curves for the  RAC beta radiation attenuating device because
of repeated mechanical failures in the tape drive and clamping
systems.  Figure  15  illustrates the instrument response  during
the 13 tests when data could  be collected.  The  two calibration
lines suggest that the performance of this continuous particulate
monitor was also  dependent  on the size of  the particulate  matter
being examined.

Continuous Monitor Reliability

     Figure 16  and Table  3  summarize the results of the  long-
term reliability  evaluation of the five continuous  particulate
monitors used in  this study.
                                143

-------
       12
    c
    3
    GO

    O
    a.
    GO
    HI
    cc

    >
          INITIAL INSTALLATION  •
          AFTER MAJOR SERVICING O
          BEST LINEAR FIT
          95% CONFIDENCE INTERVAL
                                                  I
                   6,          8         12         16

                  SAMPLING TRAIN CONCENTRATION, arbitrary units
20
               Figure 13.  Calibration data for ESC PILLS V monitor.

     It is clearly  evident  that the Lear Siegler RM 41 transmissom-
eter operated  throughout  the entire testing period without any
major servicing.  Only  routine cleaning of filters and retro-
reflector and  replacement of indicating bulbs were required.

     The RAC transmissometer experienced a blower-motor failure
after about five weeks  of operation.  However, the capacity of
the retro-reflector blower  provided sufficient purge air  to permit
the instrument to function  satisfactorily until its removal from
the stack.

     The IKOR  charge  transfer device operated during the  entire
testing program but required regular removal from the stack for
cleaning of the sensor.   Although this was a relatively simple
procedure requiring minimal time, the conditioning of the sensor
following cleaning  often  took several hours.

     Factory trained  personnel were called to the site twice
during the testing  period to make appropriate adjustments to
the ESC PILLS  V backscattering monitor.  Prior to Test 8, the
optical interrupters  and  a  printed circuit board were replaced
in an effort to eliminate the excessive base line current signal
which made zeroing  and  spanning of the instrument impossible.
When the same  problems  reappeared after Test 14, the unit was
overhauled completely.  The amount of servicing was consistent
with the field development  of any new instrument.  This was the
fourth PILLS V manufactured and the first subjected to rigorous
evaluation in  an industrial stack.
                               144

-------
c
3


to
k.
4-»

15




O
a.
co
DC
O
                         POINT

                         AT 30
        SUSPECTED ELECTRICAL SHORTS
                  BEST LINEAR FIT



         95% CONFIDENCE INTERVAL ??
     0
      0246

     SAMPLING TRAIN EMISSION RATE, arbitrary units



     Figure 14.  Calibration data for IKOR monitor.
                     145

-------
    12
.5
'E
 3
s   8
a.
O


LU
LU

CO
         BEST LINEAR FIT
95% CONFIDENCE INTERVAL|H||
            Dp<1
      048



         SAMPLING TRAIN CONCENTRATION, arbitrary units




 Figure 15.   Calibration data for RAC beta radiation monitor.
                          146

-------
     TEST NUMBER
            ^
                           Mte-
                                                          I7v  J. A            zr
                                                                 JZa           \
TESTING
IKOR
RESPONSE
1 1

II

• 1
•f 	 	 : :
I

LLS \l
ESPONSE
1 II [:|



   TESTING
LEAR SIEGLER
       TESTING
RAC TRANS
RESPONSE
                   TESTING
                RAC B GAUGE
                RESPONSE
                                     1
                                                        1
                                                                  1
                                                                                   TESTING PERIOD
                                                                                   OPERATIONAL
                                                                                   SERVICINGOR FAULT
                                                                                   (SEE TABLE 3)
                                                                                   NON OPERATIONAL
                                                                            I
                                                                                     i
                                                                                               _L
                                                                                                   _L
         MAY
             JUNE
                            JULY     AUGUST   SEPTEMBER OCTOBER  NOVEMBER DECEMBER JANUARY  FEBRUARY  MARCH
                            	1976	H	197?	1
                       Figure 16.   Summary of servicing record and operational periods of
                                  continuous monitors over a one year period.

-------
       TABLE 3.   SERVICING RECORD OF CONTINUOUS MONITORS
    Instrument
Key
Servicing or fault
IKOR
PILLS V
 Lear  Siegler RM  41
   Transmissometer
 1.    Installation complete.
 2.    Bullet sensor cleaned and turned
         horizontally and exposed at sug-
         gestion of Mr. A. Gruber.
 3.    Reading high and erratic, probe
         cleaned.
 4.    Additional cleanings required.  Mr.
         A. Gruber and Mr. E. Allen visit
         site.
 5.    Instrument functioning, however,
         showed signs of severe dust build-
         up.
 6.    Instrument removed from stack.

 7.    Installation complete.
 8.    Excessive base line current, manu-
       facturer notified.
 9.    Impossible to zero or span, serviced
         by Mr. B. Nuspliger.
10.    Full scale deflection.
11.    Returned to normal.
12.    Optical assembly retracts and blower
         fails.
13.    Major  servicing by Mr. Nuspliger and
         Associate.
14.    Optical assembly retracts, fail safe
         switch placed in "on" position in
         order to keep optics in stack.
15.    Retracts in "auto" position, again
         left in fail safe "on" mode.
16.    Instrument removed from stack.

17.    Installation complete.
18.    Fault  light, indicates dirty retro-
         reflector cleaned by Mr. T. Novak.
19.    Routine cleaning of filters and
         automatic compensation check per-
         formed by Mr. I. Kent.
20.    Operate light burned out.
21.    Light  bulb replaced.
22.    Instrument removed from stack.

                    (continued)
                               148

-------
                      TABLE  3  (continued)
    Instrument
Key
Servicing or fault
RAC Transmissometer
RAC 3-Gauge
23.    Installation complete.
24.    Blower-motor failure,retro blower
         sufficient to provide air to both
         sides of transmissometer.
25.    New blower arrived  (not installed).
26.    Instrument removed  from stack.

27.    Installation complete.
28.    Tape drive control  failure.
29.    Tape drive fault causes "double
         spotting".
30.    Operational only when tape drive
         advanced and controlled manually.
31.    Low sample volumes.
32.    Tape drive advancing continuously,
         clamping device not sealing.
33.    Major servicing by  Mr. D. Wetick.
34.    Tape drive malfunction.  Clamping
         device fails.  Instrument not
         operational.
35.    Instrument removed  from stack.
     The RAC beta radiation attenuation monitor arrived after
the completion of Test 3 because of problems experienced by the
supplier during reconditioning after use at a potential site
in the U.S.A.  Although it functioned for 13 tests, manual assis-
tance to the tape drive had to be provided for 6 of them.  Ex-
tensive on-site servicing by a factory trained technician failed
to correct the major faults.  Because of the repeated failures
in the Sampling Module the RAC 3-gauge was eliminated from the
program after Test 19.

     Of the four remaining monitors the Lear Siegler RM 41 trans-
missometer, the ESC PILLS V and IKOR 2710 were retained for a
long-term reliability evaluation because they represented three
distinctly different classes of instrumentation.  The RAC trans-
missometer was removed from the stack and further consideration
due to the blower-motor failure and satisfactory performance
of the alternate light attenuating instrument.

DISCUSSION OF RESULTS

     The interpretation of continuous particulate monitor per-
formance depends on the reliability of the manual stack sampling
data used as a standard of comparison.  This means that a thorough
appreciation of the errors and assumptions inherent in the de-
termination of particulate concentrations, mass emission rates,
                               149

-------
and aerodynamic and optical particle sizes  is needed  for  a  com-
prehensive analysis of instrument characteristics.

Random Error Analysis for Particulate Sampling Train

     The acquisition of a truly representative sample from  a
source stack involves a careful step-by-step process  using  a
sampling train consisting of several parts, each designed to
perform a specific task.  Determinations of particulate concentra-
tions and mass emission rates require a series of calculations
employing various measurements which leads  to a compounding of
errors.  Systematic and random errors are compounded  differently.

     Systematic errors were minimized by:

       i.  calibrating the S-type pitot tube - sampling probe
           assembly, integrating dry test meter, orifice  rate
           meter and stack temperature sensing element

       ii.  sampling isokinetically  to within ± 10%

      iii.  following standard procedures outlined by  the  EPS
           source testing code1

       iv.  assigning specific responsibilities to individuals
           in  the sampling team.

      Random  errors are  inherent in  any measurement.   For  any
 stack  sampling program  they can be  attributed to

        i.  source condition variation

       ii.  equipment and personnel  variations in field procedures

      iii.  equipment and personnel  variations in the  laboratory

 In the calculation of mass loading,  there will be compounding
 of 7  random  errors involving

        i.  the variance  in average  stack gas velocity

       ii.  the variance  in stack or duct cross-sectional  area

      iii.  the variance  in proportion by volume of  water

       iv.  the variance  in the average absolute stack gas tem-
           perature

        v.  the variance  in the absolute stack gas pressure

       vi.  the variance  in particulate matter collected

      vii.  the variance  in total gas sample.

                               150

-------
     Table 4 summarizes the individual measurement  variables
along with their standard deviations used  to  calculate  the  rela-
tive random errors in particulate concentrations and mass emis-
sion rates.

     In this error analysis the measurement of average  stack gas
velocity and total gas sample comprised approximately 85% of
the total random errors in the determination  of the mass emission
rate except for tests involving particulate samples weighing
less than 50 mg.  For low loading tests, the  measurement of the
particulate catch was the principal source of random error.

     Random error limits, corresponding to one standard deviation,
for the manual  sampling program have been  defined in Figures
11-15.

Particulate Matter Analysis

     Results of ESCA, X-ray fluorescence and  atomic absorption
analyses showed that lead, tin and zinc were  the three most
prominent metals encountered in the stack  emissions.

     Although the ESCA procedures provided measures of composi-
tion at particle surfaces only, the results are in  reasonable
agreement with  the atomic absorption analyses.

     It is difficult to comment on the X-ray  fluorescence results
provided by the U.S. EPA laboratories because the techniques
employed in preparing and mounting membrane samples for analysis
were not described.  When raw data in terms of pg/cm2 of filter
area were recalculated to percent of mass  reported, the levels
of lead, tin and zinc were essentially comparable to those  de-
termined by atomic absorption.  However, the  compositions ex-
pressed on a weight per cent basis by the  U.S. EPA  laboratories
are much lower  than atomic absorption determinations.  Because
of the extreme  variations in the sample characteristics it  is
suspected that  matrix effects could be responsible  for the  dis-
crepancies in the X-ray fluorescence analyses.

     The metal  composition data in Table 2 represent the results
of replicate analyses of material recovered from the sampling
nozzle, probe,  cyclone, filter and impinger components of the
sampling train.  Each of these composite samples provided a measure
of the average  composition of the stack emissions during the
period of any particulate matter concentration determination
in terms of the entire spectrum of particle sizes.  Examination
of membrane samples by X-ray fluorescence  neglected the signifi-
cant portion of particulate matter that had been collected  in
the sampling nozzle ahead of the filter.

     The recovery of material from dried beakers and filters
for the fusion  step in the atomic absorption  procedure  represented


                               151

-------
                TABLE 4.  SUMMARY OF INDIVIDUAL MEASUREMENT VARIABLES AND
                         THEIR CORRESPONDING STANDARD DEVIATIONS
       Error term
                                     Individual measurements affecting error term
                          Symbol
     Description
Standard deviation, a
NJ
   Cross-sectional flow
     area of duct, A
                    s
   Mass of particulate
   matter, M
Average stack
velocity, (Us)
based on 24   avg
local measurements
   Stack gas moisture
   content, B
             wo
                             D.
                             W
                                M
                                Vi
Stack diameter
Gross weights of filter
and beakers including
errors resulting from
washing, drying, and
weighing

Tare weights of filters
and beakers

S-type pitot tube  co-
efficient  (by calibra-
tion)

Absolute stack gas
temperature

Stack gas velocity
head (inclined manometer)

Absolute stack gas
pressure

Molecular weight of
stack gas on wet basis

Final .volume of impinger
contents

Initial volume of im-
pinger contents
    1/2  in.
     4 mg
    1/2 mg


     0.005



       5°R


    0.01 in. H20


    0.05 in. Hg
                                                                    0.1 Ib /lb-mole
                                                                          m
                                                                         0.5 ml
                                                                         0.5 ml
                                                             (continued)

-------
                                     TABLE 4 (continued)
Ul
CO

Individual measurements affecting error term
Error



term



Average stack gas
temperature (T )
Absolute
pressure,

Total gas
(Vre£'
errors in
velocity,
stack gas
Ps

sample,
including
average stack
(U )
s avg
Symbol
Vm
P
m
Tm
Ts
Pbar
P
static
K0
DN
MH
Description
Dry gas metered volume
Absolute pressure at
the dry test meter
Absolute temperature at
dry gas meter
Local stack gas tem-
perature
Atmospheric pressure
at sampling site
Stack gas static pres-
sure
Calibration constant
for orifice
Nozzle diameter
Molecular weight of
Standard deviation, a
0
0


0
0
0 01 ft' f
mm 1
n
.02 ft3
.05 in. Hg
2°R
5°R
.05 in. Hg
.1 in. H20
lbm in. Hq
Ib-mole in. H2O,
0.001 in.
, lbm






1"
°Rj
                                  m
stack gas on dry basis

Absolute pressure up-
stream of the orifice

Absolute temperature up-
stream of the orifice
    Ib-mole

0.05 in. Hg


       2°R
                                                                   (continued)

-------
                            TABLE 4 (continued)
Error term
                              Individual measurements affecting error term
Symbol
Description
Standard deviation, a
                   (AH) setting
                     (1-B  )
                     v   wo'
            Sampling time interval

            Error associated with
            setting the required
            orifice pressure drop

            Proportion by volume of
            dry gas in stack gas
            stream
                               0.5 sec

                            0.02 in. H2O



                                  0.01

-------
80 to 92% of the particulate matter caught  during  any  mass  loading
test.  Trial runs with laboratory  formulations  of  lead,  tin and
zinc compounds of compositions approximating  those of  collected
samples showed that better than 90% of  each metal  was  accounted
for after the fusion process.  On  this  basis  it is believed that
the atomic absorption procedure provided  the  most  reliable  evalua-
tion of metal levels in stack emissions.

Particle Sizing Determinations

     Because of the differences between theory  and practice,
aerodynamic particle sizes must be used with  caution.   In prin-
ciple, cascade impactors provide discrete fractions as  approxi-
mations to the true continuous particle size  distributions  that
are sampled.  The uncertainty in particle size  is  compounded
by errors associated with wall losses,  particle bounce  and  devia-
tions from theoretical calibration curves.  Evaluations  of  the
severity of these errors are topics of  current  investigations.2

     Particle bounce could have been  significant during  any test
because the impactors used for particle size  determinations
employed no substrate material on  the plates.   It  was  decided
to work with bare metal stages to  minimize  any  potential weighing
errors that could result from anomalous weight  increases in glass
fiber substrates as a result of sulfate formation  in the presence
of S02.3  The use of unlined impactor plates  facilitated quantita-
tive recovery of collected particulate  matter for  future analytical
purposes.

     According to McCain et al.,1*  particle  bounce  can  severely
distort size distributions of aerosols  having large mass mean
diameters.  As a result, the reported dimensions of distributions
with large mass median diameters could  be smaller  than  the  true
values.  On the other hand, mass median diameters  for  small par-
ticle aerosols  (whose mass median  sizes are less than  10 ym) could
be systematically larger than the  true  values because  of the
low  resolution provided by cascade impactors.

     Although it was recognized that  sampling times as  long as
4 hours could contribute to particle  re-entrainment in  the  cascade
impactor, the particle sizing train was operated as long as the
particulate loading train

       i.  to provide a check on the  mass concentrations which
           served as the primary standard for instrument evalua-
           tion

      ii.  to ensure a representative sample  for the random
           smelter process over the sampling  period.

Because of particle bounce and re-entrainment considerations,
which cannot be readily evaluated,  the  aerodynamic diameters

                               155

-------
are subject to an uncertainty approximated as ± 25% of the  re-
ported value.  However, this accuracy is sufficient for the analysis
of continuous particulate monitor performance characteristics.

     Aerodynamic particle sizes affect the performance of the
IKOR charge transfer and RAC g-attenuation devices because  both
instruments depend on particle capture from a flowing gas stream.
The light attenuating Lear Siegler RM 41 and RAC transmissometers
and backscattering PILLS V monitor respond to the optically pro-
jected sizes of particles.

     In principle, it is possible to convert aerodynamic parti-
cle sizes to optical dimensions using the relationship between
the true density of the particles under consideration and the
theoretical  1 g/cm3 standard.  This conversion becomes virtually
impossible when dealing with particulate matter whose composition
could vary from test to test and during any specific test period.
The problem  is further complicated by the fact that the geometric
standard deviation, aa, is required for computation of median
diameters on a number basis.5  Table 5 summarizes the lead, tin
and zinc compounds that could be found in varying proportions
in the stack emissions.  The colors of the materials listed are
consistent with the characteristic colors of the membrane samples
reported in  Table  2.  Because of the additions of sulfur and
sawdust  to the lead alloying kettles, elemental sulfur and  carbon
also could have been present in substantial quantities in any
sample.  Without a detailed evaluation of the density of any
test specimen  it is not possible to derive reliable optical sizes
from the aerodynamic data.

Continuous Particulate Monitor Performance

     For each  instrument, calibration curves were expressed in
terms of the best  linear fits wherever justified by the statisti-
cal "F"  test.  Error variances for each calibration curve were
evaluated and  illustrated as 95% confidence intervals.  Random
error limits for each manual particulate matter concentration
test have been indicated in Figures 11-15 in terms of one
standard deviation, a.

     In  Figures 11-15 particulate matter concentrations or
mass emission  rates have been used as independent variables be-
cause they were the primary standards against which instrument
responses were compared.

Transmissometers

     Figures 11 and 12  indicate that the Lear Siegler RM 41 and
RAC transmissometer responses are primarily dependent on particle
size when aerodynamic diameters exceed one micron.  This behavior
is consistent  with the  theoretical predictions of Pilot and
Ensor5 and the experimental work of Uthe and Lapple.7

                               156

-------
TABLE 5.  SUMMARY OF PHYSICAL PROPERTIES  OF METALLIC COMPOUNDS
     LIKELY TO BE EMITTED FROM A SECONDARY LEAD SMELTER6

Compound
Pb

PbCl2
PbCl2 .3PbS
Pb20
PbO
PbO

Pb30^
Pb203
Pb02
PbCl2.Pb(OH)2
PbCl2 -Pb(OH) 2
PbCl2. PbO. H20
PbCl2 -2PbO
PbCl2 -3PbO
Molecular
weight
207.21

278.12
995.95
430.42
223.21
223.21

685.63
462.42
239.2
519.35
519.35
519.35
724.54
947.75
Color
cubic silver
blue white
rhombic white
red
amorphous
black
tetragonal
yellow
rhombic
yellow
crystalline
red amorphous
powder
amorphous
yellow powder
tetragonal
brown
tetragonal
white
rhombic
monoclinic
prism colorless
to white
rhombic yellow
yellow
Refractive
index


2.199
2.260


2.665
2.535
2.51
2.61
2.71


2.3
2.04,2.15
2.15

2.146
2.24, 2.27, 2.31

Specific
gravity
11.3

5.85

8.342
9.53
8.0

9.1


7.21
6.24
6.05
7.08

                                                   (continued)

-------
                                       TABLE 5 (continued)
m
00

Molecular
Compound weight
PbCl2. 7PbO 1840
PbS04 303
PbSCH. PbO 526
PbS208. 3H20 453
PbfHSOit) 2 . H20 419
PbS 239
Sn 113
SnCl2 139
SnCl2 • 2H20 225
SnCU 260
SnCli, • 3H20 314
SnO 134
Sno. xH20
Sn02 150
SnC-2 . xH2O
a stannic acid
.59
.28
.49
.39
.37
.28
.7
.61
.65
.53
.58
.70

.70

Refractive
Color index
yellow crystal
or powder
monoclinic 1.877
or rhombic white 1.882
monoclinic 1.93
white 1.99
2.02
deliquescent
crystalline
cubic black 3.912
metallic
a cubic gray
3 tetragonal
white metallic
Y rhombic white
rhombic white
white monoclinic
colorless liquid
monoclinic crystal
tetragonal (cubic)
black
white powder or
yellow brown crystal
tetragonal 1.997
white, brown 2.093
black
amorphous or
colorless precipitate
Specific
gravity

6.2
6.92


7.5
5.75
7.28
6.54
3.39
2.71
2.23

6.64

6.95

                                                                   (continued)

-------
                                        TABLE  5  (continued)
en
vo

Compound
Snoa • xH20
3 stannic acid
SnSC\
SnS
SnS2
Zn
ZnCl2
Zn(OH) 2
ZnO
ZnO
ZnOa + ZnO
ZnSOi,
ZnSO,, . 6H2O
ZnSCU • 7H20
Molecular
weight

214.77
150.77
182.83
65.38
136.29
99.40
81.38
81.38
178.76
161.44
269.54
287.56
Color
amorphous or
gelatinous white
yellowish white
crystalline powder
rhombic gray
black
hexagonal gold
yellow
hexagonal bluish
white metal
cubic white
deliquescent
rhombic
colorless
white or yellowish
amorphous powder
hexagonal
white
white yellow
powder
rhombic
colorless
monoclinic or
tetragonal
colorless
rhombic
colorless
efflorescent
Refractive
index





1.687
1.713


2.008
2.029

1.658
1.659
1.67

1.457
1.480
1.484
Specific
gravity


5.08
4.5
7.14
2.91
3.05
5.47
5.605
1.571
3.74
2.07
1.97
                                                                    (continued)

-------
                                      TABLE  5  (continued)

Compound
ZnS
ZnS
ZnS . H20
ZnS03 . 2H20
Molecular
weight
97.45
97.45
115.46
181.48
Color
hexagonal
colorless
cubic
colorless
yellowish
white powder
white crystalline
powder
Refractive
index
2.356
2.368


Specific
gravity
4.087
4.102
3.98

Ol
o

-------
     In principle, the sensitivity of  a  transmissometer  shows
a monotonic decrease with  increasing particle  size  if  particulate
matter having an absorptive  index of refraction  is  involved.
However, a maximum in the  response-particle  size relationship
is to be expected according  to  the classical Mie theory  for par-
ticles having only a real  index of refraction.   Figure 17  illus-
trates the effect of the absorptive refractive  index on  the
response-size relationship for  a real  refractive index of  1.5.
Because of these size and  refractive index effects,  transmissom-
eter s should not be capable  of  detecting very  small, non-absorbing
particles, but would respond well to absorbing  particles in the
same size range.

     Most theoretical discussions involve monodispersed  particu-
late systems which are seldom encountered in real life situations.
Figure 18 shows that as the  polydispersivity of  an  aerosol in-
creases, as evidenced by increasing values of  ag, the  effect
of particle size on transmissometer response is  diminished.

     Because the stack emissions under investigation consisted
of the black and/or opaque whitish particulate  matter  and par-
ticle size distributions were of a highly polydispersed  nature,
as indicated by the high slopes of the log-probability curves,
the effects of particle size on instrument performance should
have been minimized for particles smaller than  about 1 urn  and
larger than 25 ym optical  diameter.  Consequently,  the typical
performance curves supplied  by  manufacturers showing the effect
of particle size on light  attenuation  are virtually useless for
the evaluation of the applicability of these instruments to any
specific source.

     Both the Lear Siegler and  RAC transmissometers satisfy the
U.S. EPA performance specifications.10  According to the operating
manual provided, the RAC instrument was  designed with  a  smaller
angle of view.  On the basis of collimation  considerations the
RAC device should be better  than the Lear Siegler RM 41  model.
However, a comparison of Figures 11 and  12 shows that  the  Lear
Siegler system exhibits higher  sensitivities and provides  cali-
bration curves with lower  error limits.   In  actual  fact, the
RAC transmissometer was incapable of detecting  particles,  during
this testing program, when the  aerodynamic diameters exceeded
25 vim.

Environmental Systems Corporation PILLS  V

     The PILLS V monitor provided two  calibration curves that
were relatively independent  of  particle  size.   The  two data sets
were due, most likely, to  a  change in  the instrument calibration
as a result of the replacement  of the  optics head and  other ad-
justments made during the  major overhauling  of October 11, 1976.
                               161

-------
       100
                  GEOMETRIC STANDARD DEVIATION = 2
       0.1
         0.01            0.1             1.0

               GEOMETRIC MASS MEAN RADIUS,
10.0
Figure 17.   Effect of absorptive refractive index on opacity-size
            relationship.^
                            162

-------
        ja
        0)
        D

        O
        O
        GO
        O
        cc
        HI
        CO
        z
        O
        o.
        GO
        LU
        CC
        Q
        HI

        O
        Q
        ill
        CC
        a.
           35
           30
           25
20
15
10
05
                           CARBON M = 1.96- 0.66 i
                           X = 0.56 jum
0
0.05
                                              I
           0.2     0.5    1.0    2.0

           VOLUME MEDIAN DIAMETER, j
                                              5.0   10.0   20.0
         Figure 18.  Transmissometer response as a function of geometric
                  standard deviation and volume mean diameter.9

     The calibration curve, corresponding  to the data collected
after major  servicing,  exhibits a zero off-set  and an increase
of approximately  2.3 in the "effective gain" or sensitivity.
Discussions  with  H.W. Schmitt, President of  Environmental Systems
Corporation, confirmed  that both of these  effects could be at-
tributed to  the replacement of the optics  head  and adjustments
made during  the on-site reconditioning.  The ESC personnel made
no attempts  to quantify or adjust for the  instrument changes
that could have resulted from their modifications.

     Some of the  scatter in the data collected  after the major
servicing can be  attributed to changes in  both  the real and ab-
sorptive components of  refractive indices.   Figure 19 illustrates
how a backscattering instrument would respond to particulate
matter of varying refractive index.  Additional scatter in the
data can be  attributed  to mean diameters beyond the flat por-
tion of the  PILLS V response curve and the general backscatter-
ing response curves as  shown in Figure 19.

IKOR Particulate  Monitor

     The data in  Figure 14 show that  the  IKOR monitor has limited
sensitivity  to particles smaller than one  micron in aerodynamic
                                163

-------
    104E
  «  103 -
       =  X = 0.904 /urn
  " 102
  V)
  V)
     10
  EC
  ID
  0.
  CO

  o
  Q.
  CO
     1.0
     0.1
   I—
 8 = 167°
n\2 = 0
 ag = 1.65
             \
              \
         e = 167°
       in-, = 1.96
       - ag = 1.65
         A = 0.904 jum
            I
         0.05 0.1
          0.5  1.0
5.0 10.0  0.05  0.1
0.5  1.0
5.0 10.0
          Figure 19.  Response per unit mass vs. dj, mj = 1.33, 1.40, 1.50, 2.0;
                  rr>2 = 0, 0.1, 0.3, 1.96 for backscattering. 11


diameter.   This is  not surprising  in  terms of its design prin-
ciples.   Charge transfer from particles to the sensor  can occur
only if particulate matter impinges on the collecting  head.
For the stack  conditions encountered  the impaction  efficiencies
were generally so low that only  that  fraction of the particulate
matter with diameters exceeding  4  ym  would make contact with
the sensor  surface.

     When it became apparent during the testing program that
particulate matter  with diameters  below one micron  was being
missed by the  IKOR sensor, the recommendation was made by A.
Gruber, Vice President, IKOR  Inc.,  that the sensing element be
exposed and oriented with its axis perpendicular to the stack
gas stream.   When this was done  there did not appear to be any
significant effect on the instrument  performance.

     The  wide  scatter about the  calibration curve for  particles
whose diameters are larger than  5  ym  can be due to  variations
in
                                164

-------
       i.   electrical resistivity of the particulate matter

      ii.   stack gas humidity

     iii.   stack gas temperature

      iv.   particle precharge characteristics

       v.   probe surface conditions as a result of the accumula-
           tion of particles or cleaning with abrasive cleansers,

as suggested by John.12

RAG Beta Radiation Monitor

     The RAC beta radiation  attenuating  instrument supplied  for
this program was a reconditioned  unit  which  suffered  from  re-
peated mechanical failures  in  the tape drive,  indexing and clamp-
ing components  of the  sampling  module.   Consequently, this moni-
tor functioned  during  only  13  of  22 possible testing  periods.

     According  to design principles, a single  calibration  curve
should have been obtained.   However, Figure  15  shows  that  this
instrument was  more  sensitive  to  smaller particles whose aero-
dynamic diameters were less  than  one micron.  This behavior  sug-
gests that the  RAC 3-gauge  was  affected  by particulate deposition
in the sampling nozzle and  probe  and the transport lines to  the
filter tape.  Such deposition  was confirmed  at  the conclusion
of the testing  program when  substantial  amounts of particulate
matter were recovered  from  the  nozzle, probe and boundary  layer
dilution screen.

     Neither calibration curve  passed  through  the origin.  The
observed shift  in these curves  would result  from

       i.  the  previously discussed particulate deposition in
           the  lines

      ii.  in-leakage  at the sampling  head due  to poor clamping

     iii.  filter tape losses  as  a result of de-fluffing under
           vacuum during the sampling  interval  after  taring

      iv.  filter tape losses  as  a result of abrasion during
           tape transport between taring, sampling and final
           counting.

CONCLUSIONS AND RECOMMENDATIONS

     The performance characteristics of  5 continuous  particulate
monitors were evaluated over a one-year  period  to assess  their
                               165

-------
       i.   suitability

      ii.   reliability

     iii.   accuracy

with respect to their substitution for manual methods as  a means
of ensuring long-term compliance with and enforcement of  federal
regulations pertaining to emissions from secondary lead smelters
in the Canadian environment.

     The Lear Siegler RM 41 transmissometer was more reliable
than the other four monitors.  The experimental data indicate
that this device would be suitable for monitoring emissions  from
controlled sources provided that the particulate matter had  ap-
preciable absorptive indices of refraction.  Its first order
dependence on particle sizes exceeding one micron aerodynamic
diameter makes it unsuitable for use where process variations
result in the generation of particulate matter of varying sizes,
colors and/or refractive indices.  Transmissometer performance
could not be related to changes in the chemical composition  of
the emissions.

     The Environmental Systems Corporation PILLS V monitor per-
formance was handicapped by its poor reliability and high main-
tenance requirements.  These deficiencies were consistent with
the difficulties experienced by prototype units undergoing long-
term field evaluations for the first time.  Improvements made
to the optical interrupters, controlling the zero-span band,
and provision of an external standard for referencing the band
should eliminate many of the problems encountered during  the
reliability determinations.  If the long-term reliability were
improved, the PILLS V device could be potentially more useful
than the best transmissometer because its calibration appears
to be less sensitive to changes in particle size, color and  re-
fractive index.  Variations in the metal content of the particu-
late matter could not be directly correlated to the calibration
curve for this backscattering instrument.

     Performance of the Research Appliance Company transmissom-
eter was adequate for monitoring emissions from the controlled
reverberatory mode of operation consistently producing particu-
late matter with median diameters approximating 0.5 ym.  However
it does not appear to be capable of detecting large particles    '
whose diameters exceed 25 pm.

     The IKOR 2710 particulate monitor showed limited potential
for application to either the reverberatory or lead allovina
kettle processes.  The particles passing through the baqhousP
were too small to impact effectively on the sensor   On th   t-h
hand, short, periodic bursts of high emissions durinq the nn
controlled refining operations necessitated frequent
of the sensing element.                        yuent

                               166

-------
     Because of the repeated  mechanical  failures  in  the  sampling
module of the Research Appliance  Company beta  radiation  attenuating
device supplied for the  study,  it is  difficult to comment  criti-
cally on its possible application to  measurement  of  emissions
from a secondary  lead smelter.

     Continuous particulate monitors  have not  been developed
to the stage where  particle size, shape, composition and color,
which have  pronounced effects on  instrument performance, can
be accounted for  in the  calibration curves for the instruments.
Reliable continuous monitoring could  be  possible  only if the
physical and chemical properties  of the  emissions remained suf-
ficiently constant  over  long time periods.  These conditions
are  approximated  in stacks exhausting gases that  have passed
through efficient control equipment.

REFERENCES

  1.  Standard Reference  Methods for Source Testing:   Measurement
     of Emissions of  Particulates from Stationary Sources. EPS
     l-AP-74-1, Air Pollution Control Directorate, Environmental
     Protection Service, Environment  Canada, Ottawa, Ontario,
     1974.

  2.  Harris, D.B.  Procedures for Cascade Impactor Calibration
     and Operation  in  Process Streams.  EPA-600/2-77-004,  U.S.
     Environmental  Protection Agency, Research Triangle  Park,
     NC, 1977.
                                             i
  3.  Hemeon, W.C.L.,  and A.W. Black.   Stack Dust  Sampling:  In-
     Stack  Filter or  EPA Train.  J. Air  Pollut. Contr. Assoc.
     22(7):516-518, 1972.

  4.  McCain,  J.D.,  and  J.E. McCormack.  Non-Ideal Behavior in
     Cascade  Impactors.    APCA paper  77-35.3,  presented  at 70th
     Annual Meeting,  Toronto, Ontario, June, 1977.

  5.  Pilat, M.J., and  D.S. Ensor.  Plume Opacity  and Particulate
     Mass Concentraion.   Atmos. Environ. 4:163-173,  1970.

  6.  Handbook of  Chemistry and Physics,  R.C. Weast,  Editor, 49th
     Edition, The Chemical Rubber Co., Cleveland, OH, 1968-69.

  7.  Uthe,  E.E.,  and  C.E. Lapple.  Study of Laser Backscatter
     by Particulates  in  Stack Emissions.  SRI  8730,  Stanford
     Research Institute, Menlo Park,  CA, 1972.  NTIS PB  212530.

  8.  Feldman, P.L., and  D.W. Coy.  Comparison  of  Computed  and
     Measured Opacities:  Lignite Fired  Boilers.   APCA paper
     73-168, presented  at 66th Annual Meeting, Chicago,  IL, June,
     1973.
                               167

-------
 9.   Markowski,  G.R.,  G.J.  Woffinden, and D.S. Ensor.  Optical
     Method for  Measuring the Mass Concentration of Particulate
     Emissions.   EPA-600/2-76-062, U.S. Environmental Protection
     Agency,  Research  Triangle Park,  NC, 1976.

10.   Nader, J.S.,  F. Jaye,  and W.  Connor.  Performance Specifica-
     tions for Stationary-Source Monitoring Systems for Gases
     and Visible Emissions.   EPA-650/2-74-013, U.S. Environmental
     Protection  Agency,  Research Triangle Park, NC, 1974.

11.   Miller,  A.C.   Theoretical Modelling and Calibration for
     a Particulate Mass  Concentration Monitor.  M.S. Thesis,
     The University of Tennessee,  Knoxville, TN, August, 1977.

12.   John, W.  Investigation of Particulate Matter Monitoring
     Using Contact Electrification.   EPA-650/2-75-043, U.S.
     Environmental Protection Agency, Research Triangle Park,
     NC, 1975.
                               168

-------
                              PAPER 8


            AN  IN-STACK FINE PARTICLE  SIZE SPECTROMETER;

            A DISCUSSION OF ITS DESIGN AND DEVELOPMENT
                       ROBERT G.  KNOLLENBERG
                 PARTICLE MEASURING SYSTEMS,  INC.
ABSTRACT
     The development of an in-stack fine particle size measur-
ing device for the EPA has been underway at PMS  for  the past
several months.  The instrument utilizes a laser fed optical
system with detection by near-forward light scattering.  Sam-
ple volume is established through the use of a high  resolution
imaging system using paired detectors viewing the sample plane
through a masked beam splitter.  The instrument  covers a 0.3
to 10.0 yrn size range with 60 channels resolution.   Absolute
theoretical accuracy is ±20% of size for completely  unknown
refractive index.  The instrument is designed to operate con-
tinuously at in-stack temperatures up to 250°C at flow velocities
up to 30 m/sec.  Flow velocities are determined  from measured
particle transit times through the laser beam.   Internal probe
components are cooled by a water jacket and external heat ex-
changer.  The heat exchanger, probe pulse processing electronics,
data acquisition system and operating controls are housed in
a central electronics console.  The instrument is being tested
on a local coal fired power plant.  Its eventual use will be
directed at the characterization of particulate  emissions of
stacks or other stationary sources and to qualitatively evaluate
the performance and collection efficiencies of particulate con-
trol devices now in operation.

INTRODUCTION

     In September, 1977 Particle Measuring Systems,  Inc.  (here-
after PMS) was contracted by the Environmental Protection Agency
(hereafter EPA) to design, fabricate, and evaluate an  in situ
Fine Particle Stack Spectrometer System  (FPSSS).  The  FPSSS will
                                169

-------
be used to characterize the particulate emissions  of  stacks  and
other stationary sources and to quantitatively evaluate  the  per-
formance and collection efficiencies of particulate control  de-
vices now in use.  The EPA design criteria that  the FPSSS  had
to satisfy were to provide in situ high resolution particle
sizing over a size range from 0.5 to 5.0 urn diameter  with  con-
centrations in this range above lOVcm3 and integrated partic-
ulate loading from 0.3 to 3.0 g/m3.  The FPSSS is  also required
to operate at temperatures from 20 to 250°C and at flow velocities
from 1 to 30 m/sec.   An operational prototype instrument has
been designed and fabricated and initial performance  testing
begun.  This paper describes the current status of this develop-
mental effort.

     The basic design approach followed in the FPSSS  utilizes
existing technology.   There are three major areas of  prior work
which have provided the needed technology base upon which  the
underpinnings of the FPSSS design could be established.  These
are:

     1)   The PIONEER VENUS Large Probe Cloud Particle Size Spec-
         trometer (LCPS),1 development work with joint involve-
         ment of PMS and Ball Brothers Research Corporation
          (BBRC).

     2)   The recent experience by PMS in stack measurements using
         plumbed instruments.

     3)   The well developed PMS technique of utilizing high reso-
         lution imaging systems with light scattering to perform
         in situ single particle size measurements.

     The current prototype FPSSS instrument would appear to meet
the original EPA design objectives.   It has a near-forward light
scattering optical system with an expanded 60 channel 0.3  to
10.0 ym size range divided into four subranges of 15  size  chan-
nels each.  The instrument is capable of relatively accurate
measurements at concentrations up to 105/cm3 without  regard to
refractive index.  An optical velocimeter has also been designed
into the FPSSS.  The instrument operates continuously at 250°C
temperatures utilizing a water-cooled head design and external
heat exchanger.  Extensive theoretical modeling of thermal as
well as optical performance has been utilized in configuring
the FPSSS Probe head.  Wind tunnel facilities at PMS  have  played
an extremely important role in measuring aerodynamic  impacts
of the FPSSS sampling section.  Calibration has included lab-
oratory and wind tunnel tests on particulates having  known or
independently verifiable size distributions.  Field tests  on
an operating coal-fired power plant stack began in April,  1978
and some preliminary results are presented here.
                               170

-------
DESIGN APPROACH OF THE  FINE  PARTICLE STACK  SPECTROMETER SYSTEM
(FPSSS)

     A hot stack environment may  appear  to  present possibly too
high concentrations  for  in situ single particle  measuring  devices;
however, measurements with a standard laboratory aerosol spectrom-
eter manufactured by PMS employing  a ducted sample flow showed
this not to be the case.  Today most sources must  comply with
much more stringent  emission  controls.   The standard compliance
device for coal-fired power  plants  is an opacity monitor which
measures total extinction.   Permissible  emissions  generally  com-
pute to extinction coefficients less than 3 x  10~Vcm.   This
would correspond to  a visibility  of  approximately  120 meters
and maximum concentrations around 5  x 103/cm3  for  1 ym  radius
particles.  Such concentrations are  well within  the range  of
standard aerosol spectrometers offered by PMS.   The real problem
is performing measurements in the hot environment.  The stack
is often well above  boiling  temperature  and if continuous  mea-
surements are desired the instrument must be cooled to  survive.
Our approach was to  provide  a reasonable thermal environment
for an existing PMS  light scattering spectrometer  electro-optical
system using an active  cooling system.

     The FPSSS design involves a  laser fed  high  resolution imaging
optical system with  particle detection and  sizing  by strong  for-
ward light scattering  (see optical  system in Figure 1).  The
imaging system provides  accurate  sample  volume definition  and
enables accurate particle transit time measurements to  extract
flow velocity.  The  FPSSS sampling  head  design shown in Figure
2 reveals a water cooled insulated  electro-optical system.   The
probe head communicates  to a standard PMS Data Acquisition System
 (DAS) and thermal control system  packaged in a control  console
 (see Figure 3).  The FPSSS Probe  has now been  fabricated much
as shown in Figures  1 and 2;  however, the subsystems within  the
control console are  still evolving  and will eventually  be  re-
packaged.

     The development of  the  FPSSS was not considered a  high  risk
task although  it did require the  application of  diverse and  de-
manding technology.  The performance requirements  are  within
the range of standard PMS instruments (with the  exception  of
the high temperatures involved).  Extensive use  has been made
of prior success in  developing technology to perform measurements
in even more severe  environments.   For instance, the Cloud Par-
ticle Size Spectrometer  developed for NASA  and  the PIONEER VENUS
payload must withstand  450°C.1'2  This technology  base has been
applied to design the FPSSS.  An  80  node thermal model for the
probe head was developed by  BBRC  predicting cooling requirements,
thermal gradients and mechanically  induced  changes in  optical
alignment.  The design  in Figures 1 and  2 primarily reflects
efforts to minimize  alignment error  predicted  by the model.
The optical system design, scattering response,  and thermal

                               171

-------
 design will be detailed  here.  The actual  hardware description
 is deferred to the section in which the  prototype is discussed,
 below.
                 5mW He-Ne LASER
                                                  ADJUSTABLE BEAM
                                                  STEERING MIRRORS
DETECTOR
MODULE
 BEAM
SPLITTER
       SECONDARY
       20- OBJECTIVE
                                                                 7cm RADIUS
                                                                 CONDENSING BEAM
                                                                 FOLDING MIRROR
                                                      OBJECT PLANE
                                                 AR COATED
                                                  WINDOW
                                                          LASER BEAM DUMP
                                                          SPOT
               Figure 1. Fine particle stack spectrometer probe optical system.
                            LASER MODEL 80-5T
     STAINLESS STEEL BOOM        (COHERENT RADIATION)
HIGH VOLTAGE          REFERENCE DETECTOR  \
LASER LEAD  -^
  OUTPUT   ^
  WATER LINE
    SIGNAL _. 't_-
    CABLES   ^
     INPUT
     WATER
     LINE
    STAINLESS
    STEEL INSULATION
    RETAINER AND COVER
                                   FIBERGLASS
                                   INSULATION
                                                    HIGH REFLECTIVITY FLAT
                                                    MIRROR <2>
                                                                        HEATER
                                                                   PURGE AIR
          PHOTO DETECTOR
          ASSEMBLY
                                    \
                                 BEAM
                                 SPLITTER
                                                                AIRFLOW
                                                              PURGE AIR
20x NIKON
MICROSCOPE
OBJECTIVE
               /
              HIGH REFLECTIVITY
              MIRROR 7.5mm
              RADIUS
LOW LOSS AR COATED
WINDOW
                  Figure 2. Fine particle stack spectrometer probe head.

  FPSSS  Optical  System Design

       The optical system  became  the  primary design  driver  in the
  FPSSS.   Its alignment  is  the single most  important optical  param-
  eter requiring  control.   The optical system shown  in Figure 1
  is essentially  identical  to that  originally proposed to the EPA.
  The output of  a 5 mW high order multimode  laser  is directed to-*
  wards  a  7 cm radius condensing  mirror by  a pair  of plane  mirrors,
  The condensing  mirror  focuses the laser beam down  to approxi-
  mately 125 ym  diameter at the object plane of the  light collect-
  ing/ imaging system.   The laser beam then  expands  to approxi-
  mately 3 mm diameter before being absorbed by a  dump spot on
                                    172

-------
    PROBE
    ELECTRONICS
       I SIGNAL _,
       CABLE
TO FPSSS;
PROBE   'WATER'
       LINES -~
                                                      MASTER
                                                      CONTROL
                                                      PANEL
THERMAL-CONTROLLER
                RESERVOIR WATER PUMP
                                         HEAT EXCHANGER
                      Figure 3. FPSSS data/control console.


  the FPSSS window.   Particles in the vicinity of the object plane
  scatter energy  through the window which is collected by  the prime
  objective  (F/1.8,  50  mm f.l.)  and relayed at 2:1 magnification
  to the secondary  objective which is a 20X Nikon microscope ob-
  jective operated  at 10X.   The total magnification  is thus  20X.
  The final  image is produced on a pair of exit faces of a beam
  splitter.  The  reflected  image face is masked with a 0.78  mm
  wide vertical mask aligned in the direction of particle  flow.
  The second transmission prism face is unmasked.  A pair  of photo-
  diodes and their  associated preamps view the particle  images
  through each prism face.

       The capabilities of  this optical system are of a  fundamental
  nature in  that  they provide a means of defining a  desired  sample
  volume effecting  the  in situ measurement capability.3'4'5  The
  masked beam splitter  derives two signals, which in conjunction_
  with double pulse height  analysis, provide a means of  determining
  if a particle's position  is in the desired sample  volume.  The
  relative size of  the  sample volume cross section with  respect
                                  173

-------
to the laser beam is depicted in Figure 4.  The sample  volume
includes only the region near the center of the laser beam.
The sample volume cross section is noticeably diamond shaped-
The center of this diamond cross section coincides with  the  ob-
ject plane of the collecting optics.  The points of  this  diamond
cross section define the limiting depth-of-field of  the  FPSSS.
Both the width of the cross section and the depth-of-field vary
inversely with the magnification used in the collecting  optics.

     The diamond shaped sample cross section results from the
accept/reject criteria used in comparing signals at  the  masked
and unmasked detectors.  The light transmitted on axis  through
the beam splitter is the signal used to size the particles.
The light reflected at 90° forms its image on a circular  aper-
ture with the central opaque vertical mask.  Shown in Figure
5 are the size and positions of images formed by particles at
various positions in the illuminated volume.  It is  important
to understand that for small particles (essentially  point ob-
jects) the  image size is only a function of its axial displace-
ment from the object plane.  The image size is linearly  related
to the numerical aperture of the collecting optics and  is given
approximately by:


     Image  size = N.A. x displacement from object plane-

It is apparent that only images that are near the object  plane
and the center of the sample volume form images with light con-
centrated on the 'opaque mask as illustrated in Figure 5.  Thus,
such images transmit little signal through the masked aperture.
Particles whose pulse amplitudes, as seen by the masked aperture
detector, are greater than those seen by the signal aperture
detector are rejected.  This defines the diamond shaped  sample
cross section and image relationships shown in Figure 6.  We
use a gain  ratio of masked aperture detector to signal aperture
detector of 4X for best noise immunity.  The sample cross section
area is the product of the sample volume width and one-half  the
depth-of-field.

     One final aspect of the sample volume needs explanation.
As we have  defined it the sample volume is only the  region of
accepted measurements.  The total view volume includes a  much
larger volume where both accepted and rejected particles  are
viewed.  This view volume is as much as ten times larger  than
the sample  volume, and must be used for coincidence  error esti-
mates.  The ratio of the sample volume to view volume is  a func-
tion of the inner numerical aperture of the collecting solid
angle (2°,  N.A. = 0.03).  This presents an obvious trade-off
between a design to collect very strong forward scattering and
one which maximizes measurements at the highest concentrations
                               174

-------
                     OBJECT PLANE
    SAMPLE VOLUME
    CROSS SECTION
                                                1/E2 INTENSITY
                                                 (BEAM EDGE)
                                                         HIGH ORDER
                                                         MULTIMODE
                                                          INTENSITY
                                                         DISTRIBUTION
MAXIMUM VARIATION
 IN INTENSITY OVER
 SAMPLE VOLUME
          Figure 4. Relative size and position of sample volume cross section.
Theoretical Optical Performance

     The optical  system discussed in  the  previous section was
obviously constrained by several factors.   The FPSSS collecting
solid angle of  2  to 11° is smaller  than  that employed in standard
aerosol spectrometers offered by PMS  (4  to  22°).   This collecting
solid angle has primarily evolved from  the  alignment analysis
incorporated  in the thermal model.  The  2°  inner  angle can be
increased but the 11° outer angle cannot  be increased without
moving the object plane closer to the probe window or increasing
the lens diameter.   The latter choice may induce  some flow errors,
Wind tunnel results of flow through the  present sample volume
location insure sample flow velocities  within 5%  of free stream.
The option of increasing the inner  angle  remains  and more will
be said in this regard in the section on  future work; however,
all theoretical computational work  thus  far has used the 2 to
11° collecting  solid angle.

     The computed optical response  curves along with some ex-
perimental data points are presented  in  Figure 7.  The oscillat-
ing curves presenting the results of  Mie  scattering computations
for real indices  should be viewed as  worst case in that the ef-
fects of laser  beam convergence and multimode characteristics
have not been included and all particles  are nonabsorbing  (any
                                175

-------
MASKED APERTURE
              APERTURE AT
               PRISM FACE
                                             0.78 mm

                                              - 2.50 mm
J APERTURE AT
 PRISM FACE

    	IMAGE
          PLANE
SIGNAL APERTURE
                                                                               TO OBJECT PLANE
                             IMAGE PLANE
                 Particle Image at end of
                 Depth-Of-Field at center
                 of Sample Volume Width
                 Particle Image within
                 Depth-Of-Field and within
                 Sample Volume Width
                 Particle Image near
                 Object Plane and center
                 of Sample Volume Width
                                           BEAM SPLITTER
Particle Image at end of
Depth-Of-Field but
outside Sample Volume
Width
Particle Image within
Depth-Of-Field but
outside Sample Volume
Width
Particle Image near
Object Plane but
outside Sample Volume
Width
               Figure 5. Image sizes and positions on masked aperture detector.
                           OBJECT PLANE
                                                                        MASKED APERTURE
                                                                            SLIT WIDTH
                                                                   T
                     LIMIT OF DEPTH-OF-FIELD
           Figure 6. Image size as a function of sample volume position for the
                    case of 4X gain ratio of masked-to-signal aperture.
                                            176

-------
       BOUNDARY OF UNCERTAINTY
                                            BEST FIT CALIBRATION CURVE
                BOUNDARY OF UNCERTAINTY
            0.5 ±0.12 urn
                                              O LATEX PARTICLES
                                              • GLASS BEADS
                                        3.0
4.0
5.0
                               RADIUS,
          Figure 7. Theoretical Mie scattering for 2-11 o real indices 1.4, 1.5,
                 1.6, and 1.7.

of these will reduce the amplitude of  the oscillations).  Thus,
the error bounds  apply to all  indices.   Small amounts of absorp-
tion simply  reduce the amplitude  of the oscillations, as well
as the probable  error, and few particles would be expected  to
be completely nonabsorbing.  The  effect of absorption is illus-
trated in Figure  8 for a single real index of 1.4 and complex
index values of  O.OOli, O.OOSi, and O.Oli.

     The bounded  results presented in  Figure 7 represent sizing
tolerances for all particles,  i.e., particles with higher and
lower indices or  absorbing particles will still fit within  the
envelope given.   However, what we really desire is the  average
error expected.   Using the best fit calibration curve presented
this would be within 10% of actual size.  The latex and glass
                                177

-------
particles, in fact, show errors to be considerably less  than
that theoretically predicted.  This is partially due to  beam
convergence and laser multimode properties as well as  the poly-
dispersion in the case of the glass beads.  In general,  the
results are better than expected considering the many  compromises
involved in configuring such an instrument.

     The choice of the collecting solid angle has been largely
dictated by other design constraints; however, it is nearly as
good a choice as any other set of angles.  Strong forward scat-
tering is quite insensitive to particle shape because  the
diffracted light contribution is itself a function only  of cross
sectional area.  It also provided the greatest .working distance
for viewing particles and thus enabled more nearly in  situ mea-
surements.

Thermal Analysis

     Single particle size spectrometers designed to operate at
high particle concentrations and at small size require an ex-
tremely small view volume.  Ordinarily, the beam width must be
small  if  the view volume is to be small.  A laser is required
to produce beam widths of 100 ym dimension if any useful energy
density is to be achieved.  In the FPSSS this beam must  stay
essentially fixed with respect to the imaging system if  the beam-
splitter  detector set is to view particles in the same region
of the laser beam cross section.  Because of the high  order multi-
mode beam  intensity profile a movement of ±25% of the  beam width
 (25 )jm or  0.001 in.) is tolerable.  The essential thermal problem
is thus to prevent a transverse beam movement of one mil over
a 250°C temperature range.  The general problem of cooling the
laser  electronics and optics to a tolerable temperature  is trivial
by comparison.  Looking at the optical system in Figure  1 and
the probe  head  in Figure 2 it can be seen that only two  optical
components see  the high temperature environment 	 the  7.5 cm
radius mirror and the window.  All other elements are  within
the insulated water-cooled regions.  The window has zero power
and thus  cannot introduce alignment errors except by tilting,
which produces  a negligible beam offset as long as it  is per-
pendicular to the optical axis to within a couple of degrees.
The 7.5 cm mirror is thus the single element of concern.

     The  80 node thermal model was used to predict the thermal
effects on alignment as well as cooling requirements.  First
the optical effects of thermal-mechanical movement of  the laser,
all mirrors and the windows were measured using an optical brass-
board with x, y, z translation stages.  The thermal model then
provided  the positional data for optical elements from which
changes in alignment were calculated.
                               178

-------
     The most important  results  of  the  thermal  analysis  can  be
summarized as follows:

     a)  Maximum cooling  load  of 765  watts  is developed  at 250°C
         and 30 m/sec velocity with 20  feet of  support boom  (see
         below).

     b)  The internal head  can be maintained to within 3°C of
         ambient outside  air  temperature (as seen  by heat ex-
         changer)  at a  1  gpm  coolant  flow rate.

     c)  Internal  head  temperature  gradients are less than 1°C.

     d)  The alignment  is only sensitive to cross  gradients  be-
         tween  the two  support arms holding the external 7.5
         cm mirror mount.

     The resulting FPSSS head design  reflects  these results  in
subtle ways.  The  internal  head  body  must be fabricated  from
like material with high thermal  conductivity and high thermal
mass 	 aluminum  was selected.   The  external mirror support
arms should have low thermal  conductivity and coefficient of
expansion  	 stainless steel was found adequate.   Since these
support arms attach directly  to  the cooled  aluminum inner head
body they  must  withstand the  nearly full temperature gradient
from outside ambient to that  inside the stack.   It is always
desirable  to maintain maximum gradients in  the  most stable ma-
terials, thermally.

DESCRIPTION OF  THE PROTOTYPE  FPSSS

     At the time of this writing the  FPSSS  design is nearly  com-
plete  but  only  certain  subsystems have  been fabricated  and tested,
The final  FPSSS will contain  a dedicated intelligent DAS instead
of the  standard DAS shown in  Figure 3,  which will be capable
of real time computations of  size and mass  distributions, mass
loading, and extinction coefficient (or opacity).   However,  it
was found  highly desirable  to make  preliminary  in-stack  measure-
ments  to determine the  scope  of  the DAS requirements, as well
as uncovering any  probe problems early.   For the preliminary
test work  an existing Model CSAS-100  Classical  Scattering Aerosol
Spectrometer electronics  console satisfied  the  DAS requirements.
Furthermore, because of the great similarity in the FPSSS elec-
tronics to standard PMS instruments preliminary measurements
could be made with existing probe electronic subsystems  as well.
Pulse processing electronics  and pulse  height  analyzers  were
fabricated and  installed  in the  CSAS-100 electronics console.
Other fabricated subsystems include the FPSSS  head, support  boom,
thermal control system  and  port  bearing assembly.   These sub-
systems are shown  in Figures  9 and  10.
                                179

-------
z
(3
CO
O

E
U i02
o) IU
co
LLJ
CC
  101
  10°
     m = 1.4-0.0101-
     m = 1.4-0.005i-
     m = 1.4-0.001 r
        f

        f
                 1.0
                             2.0           3.0
                                 RADIUS, jum
4.0
5.0
               8. Theoretical Mie scattering for 2-1Jo absorbing particles with
                 1.4 real index.
FPSSS  Head

     The head of  the prototype FPSSS  illustrated  in  Figures  2
and  3  is shown  in Figure 11  with the  insulation retainer split.
The  head is approximately  20 in. long,  has a 2.25  in.  x 3.5  in"
elliptical cross  section and weighs seven pounds.  The head  body
is fed by two water lines  which have  circuitous paths runninq
the  full length of the head  body making several internal bends

                                  180

-------
before running back  to  the  rear  and  exiting.   Thus,  four water
lines are fed through the boom.   Two high voltage laser leads,
a multiconductor  signal cable,  and an air line also  feed through
the boom to  the FPSSS head.

     The optical  system is  identical to that  described above.
The laser is mounted on "0"  rings without adjustments.  The only
adjustments  are x-y  adjustments  on the first  beam-folding mirror
and the 7.5  cm mirror.   The  adjustment on the 7.5 cm mirror was
not initially planned;  however,  it was found  necessary when we
discovered that adjustment  using the beam folding mirror had
near zero effect  at  the object  plane by virtue of the object
plane being  centered at the  focus of the 7.5  cm mirror.

     The head body was  constructed in three  sections to gain
access to the various optical element cells  and for  machineability,
"0" ring seals are used for  the  water paths  and sealing is posi-
tive up through 100  psi. The photodetector  assembly loads from
the rear end can  be  removed  without splitting the head body.

     Purge air was provided  only for the 7.5  cm mirror initially.
This element has  a small aperture and is easily purged.  Con-
tamination on its surface is, however, more  critical than on
the window.  We eventually  plan  to purge the  window, as well,
but did not  initially  in order  to determine  its potential ex-
posure and rate of contamination.

FPSSS Support Beam and  Port  Bearing

     The FPSSS is designed  to permit installation on a stack
port flange  and penetrate into  the stack to  any desired length
in order to  sample continuously  across the stack. This has been
accomplished using a sectioned  tubular support boom  which can
be fed through a  lateral bearing mounted to  a stack  port flange.
All water lines and  electrical  cables are continuous through
all boom sections.   To  add  a section it is merely necessary to
screw it into the preceding  one.  The first  boom section is nor-
mally left mounted to the probe  head and all  boom sections are
of 5 feet length. The  boom  sections are constructed of thin-
walled stainless  steel  tubing.   Approximately 0.5 in. of fiber
glass insulation  and an inner 1.125  in. I.D.  PVC sleeve allow
sufficient room to slide the lines and cables when joining and
separating sections. Each  boom  section adds  about 6 pounds of
suspended weight  although the final  section  is slightly heavier
due to a larger wall thickness  required for  the increasing loads.

     The port bearing design is  of a clamshell nature and is
split to allow passage  of the larger probe head.  Once the head
is by the bearing it is closed  forming a snug fit to the 2.5
in. O.D. stainless steel walls  of the boom sections.  The lateral
bearing has  four  sets of four concave stainless steel rollers.
                                181

-------
Thermal Control System

     The thermal control system was  rather  simply constructed
using a small centrifugal pump, an automotive type heater radia-
tor, instrument blower and storage reservoir all packaged in
a single housing.  The purge air  pump  is  also currently housed
in the thermal control system.  The  water pump has a throughput
of 1 gpm with 30 feet of line and a  corresponding pressure drop
of 7 psi.  Quick disconnects are  used  on  all lines.

FPSSS Probe Electronics

     A block diagram of the FPSSS Probe electronics is shown
in Figure 12.  The section enclosed  in the  box containing the
preamps and photodiodes is a separate  module housed inside the
FPSSS Probe head.  The amplifiers have a  minimum bandwidth of
300 KHz.  The second stage is a programmable amplifier used to
gain switch between size ranges.  The  two diodes with their
preamps provide the signals which make it capable of distinguish-
ing whether a particle is within  the proper  sample volume and
rejecting particles which are not.   A  reference detector con-
structed using a photodiode and an appropriate amplifier is also
inside the FPSSS Probe head.  This reference detector provides
a reference signal proportional to the power output of the laser.
Changes in laser output are thus cancelled  when the signal is
applied as the reference input of the  pulse  height analyzer.
        Figure 9. Photograph showing the FPSSS head mounted to the section*!
              boom and CSAS- WO electronics console.
                               182

-------
       Figure 10. Photograph of FPSSS port bearing assembly and heat exchanger.
     The remainder  of  the  FPSSS electronics are contained in
the CSAS-100 Electronics Console.   The two signal pulse streams
are first properly  leveled with baseline restoration and DC off-
set circuitry.  Dual peak  readers  then momentarily store the
pulse heights  from  both  the signal and masked aperture detectors.
The peak readers  are used  to provide inputs to a comparator to
determine which of  the two pulse heights from the preamps is
the greatest.  This measurement determines when particles are
in the accepted sample volume.

     A pulse height analyzer sizes the signal pulses of all par-
ticles passing through the beam.  The pulse height analyzer has
a set of sixteen  voltage comparators and latches.  The reference
voltage to the comparators provided by the reference detector
is divided by  resistive  dividers.   Because its reference voltage
is derived from the source of illumination, the entire system
has an effective  automatic gain control (AGC).

     The transmit time analyzer measures the half-width of delayed
pulses that are found  to be in  the sample volume.  The transit
times are averaged  over  a  great number of particles to provide
a true statistical  velocity average (note that velocity is actu-
ally the reciprocal of transit  time).
                               183

-------
           Figure 11.  Photograph of FPSSS partially disassembled revealing
                   construction insulation details.
between
     The control
                  (accept/reject)  logic provides the proper  delay
        an event  and  the  strobe  and  reset pulses.  This  logic
also provides gating  for  valid and  invalid strobes.
     The pulse height  analyzer  is currently configured  to  provide
four size ranges of  15  channels  each as follows:
     Range 0  2.5
     Range 1  1
     Range 2  0.5
     Range 3  0.4
                     10     Mm
                      5.5   pm
                      2.0   urn
                      0.85  ym
All size intervals  are  linear  with maximum resolution  in  Range
3 being 0.03 ym.  The ability  to switch ranges has  been  found
to be particularly  important in field measurements.  Calibra-
tions with particles of known  size have been performed previously
using latex spheres and glass  beads with results  shown  in Fiqure
7.

RESULTS OF INITIAL  IN-STACK TESTS

     The first  tests of the FPSSS were conducted  at the  Valmont
Power Plant owned and operated by the Public Service Company
of Colorado on  April 24, 1978.  This is a coal-fired power plant

                                184

-------
with general operation  and  control devices similar to that de-
picted in Figure  13.  Measurements were performed at the 80 foot
level on the stack  which  afforded good access and at which a
Lear Siegler Model  RM41 Opacity Monitor was also operating.
These initial  tests were  limited to an hour of measurement time
with the entire set-up, measurement,  and pack-up completed in
less than two  hours.

     Measurements were  taken at  two foot  intervals  from  3  to
17 feet in-stack penetration.   The  stack  had  an  I.D.  of  21  feet
and we did not have  sufficient  boom to reach  completely  across.
However, the measurements revealed  a  symmetric profile of  par-
ticle flux and the  lack of  measurement over the  final four  feet
was not regarded as  significant.

     The in-stack velocity  profile  revealed a greater amount
of turbulence  than  anticipated  with gusts of  5 m/sec  common near
the stack center.   The  mean flow varied from  5 to 12  m/sec  with
the highest values  at the center.   No regions of reverse flow
could be identified.

     The particle size  distributions  measured at 2  foot  intervals
were surprisingly uniform as viewed on the CRT spectral  display
of the CSAS-100 electronics console.   In  fact, once corrections
for variations in flow  rate were made the distributions  revealed
only minor spatial  spectral differences which were  of the  same
order as temporal changes at a  fixed  location.   For this reason
all measurements were integrated together to  generate a  single
average particle  size distribution  representative of  the entire
stack  (see Figure 14).  The particle  size distribution is  seen
to be highest  in  number at  the  smallest size  (0.4 urn) although
the slope is decreasing.  The overall slope is quite  steep.
In fact, it is steeper  than observed  ambient  background  in many
cases.  A size distribution with such a steep slope is charac-
teristic of air passed  through  coarse filters.

     The computed average distribution of extinction  cross sec-
tion  (2nd moment) as a  function of  particle size is given  in
Figure 15.  Thg extinction  cross section was  computed for  a wave-
length of 5500A in  an effort to make  comparisons with the  opacity
monitor operating with  a  white  light  source with its  spectral
maximum at this wavelength. The extinction cross section  is
seen to peak at sizes of  0.5 to 0.6 ym and has an integral value
of 3.0 x 10l*ym2/cm3.  The  integrated  cross section over  the 6
meter stack diameter provides a computed transmission of 0.83
or an opacity  of  17%.   The  Lear Siegler RM41  had comparable opa-
city values of 14 to 16%  during the period of measurement.

     The close agreement  between the  Lear Siegler RM41 and the
FPSSS opacities must be regarded as fortuitous at the present
time.  A certain  amount of  particle cross section also exists
below the 0.4  ym  lower  limit of sensitivity although probably


                                185

-------

MASKED
APERTURE
DETECTOR
SIGNAL
APERTURE
DETECTOR H>

  BIAS
                                                 SAMPLE
                                                 VOLUME
                                                 VALIDATION
                                                 COMPARATOR
                                                        TRANSIT
                                                        TIME
                                                        ANALYZER
                                                            MEAN
                                                            VELOCITY
                                                                   TO DAS
                                           PULSE
                                           HEIGHT
                                           ANALYZER
                                                      ACCEPT
                                                      REJECT
                                                      LOGIC
                  Figure 12.  FPSSS probe electronics block diagram.
   less than 10% of the total.   The  exact  spectral characteristics
   of the Lear Siegler RM41 were not available and in this size
   range extinction is a strong  function of  wavelength.  Further-
   more, an ideal transmissometer still gains contributions from
   multiple scattering which were neglected  in our treatment.
   Finally, the soiling of the window resulted in a small but ob-
   vious underestimate of particle size and  opacity.

        The average particle volume  (mass) distribution (3rd moment)
   is given in Figure 16.  This  is probably  the most interesting
   of all the spectral plots.  It reveals  several dominant mass
   modes each being statistically valid.   Perhaps most surprising
   is the dominant mass mode at  0.65 ym.   It is more striking when
   presented with the full resolution of Range 3 as shown in Fig-
   ure 17.  Here there is little doubt that  the FPSSS has captured
   nearly all of the mass.  The  integrated mass loading is surprisingly
   low being on the order of only 0.01 to  0.02 g/m3, depending on
   the assumed density.  The known undersizing due to the soiled
   window should have only resulted  in underestimates of mass less
   than 30%.

        We expected mass loadings nearer a tenth of a gram; however
   the only way in which higher  mass loading values would be com-   '
   patible with opacity values of less than  20% (regulatory com-
   pliance value) would be with  an increase  in size and decrease
   in concentration over that observed.  A simple increase in size
   of a factor of two provides an eight-fold mass increase but also
   a four-fold increase in cross section and opacity   Since the
                                   186

-------
00
-O
                                                                      MAIN STREAM
                                                                               TURBINE
                                                                                        GENERATOR  SWITCHYARD
         COAL SUPPLY   CRUSHER^
                       HOUSE
                                                                     COLD REHEAT i
                                                                     HOT REHEAT)Ife-r=i
                                                                     FEED WATER PUMP
                                                                     HEATERS
                                                                                                           COOLING TOWER
                               PULVERIZERS
                                             FORCED DRAFT
                                             FAN
                                                        ASH DISPOSAL
                                                                       REHEATER
                                 Figure 13.  Schematic drawing of a steam electric generating station.

-------
mass-to-cross section ratio is proportional to radius,  or  size,
it is necessary to increase size by a factor of  ten  and decrease
concentration by a factor of 100 to maintain the same opacity
but a factor of ten higher mass loading.  Either of  the above
is totally unreasonable from an instrumental standpoint.  We
are thus left to conclude that this particular stack does  indeed
have a low mass loading characterized by particles of about  1.3
ym diameter.

FUTURE WORK AND CONCLUSIONS

     We are encouraged to believe that the FPSSS will be a satis-
factory instrument for making in situ size distribution measure-
ments in a hot stack environment.  However, field testing  has
only begun and final assessment must await much more exhaustive
work on other stacks and stationary sources where particulate
characteristics may be quite different.  Results of measurements
ahead of the control devices in the Valmont stack are currently
being analyzed.  Evaluation of control devices by performing
measurements up and down stream is a goal of the FPSSS  develop-
ment.  Suffice to say a great deal of work remains.

     It is helpful when analyzing the performance of a  new in-
strument to bear in mind the trade-offs made in  its design.
With regard to the FPSSS two come to mind immediately.   One  has
resulted in the current size limit of 0.4 ym and the other may
prove to limit the maximum concentration to a lower  level  than
desirable.  These two factors are strongly coupled.

     The EPA initially asked for a size range of 0.5 to 5.0  ym.
We felt that a 0.3 ym sensitivity could be obtained.  Our current
instrument has a 0.4 to 10 ym range.  The difference between
0.3 and 0.4 ym is about a factor of five in signal.  An expansion
of the collecting angles from 11 to 20° would pick up the dif-
ference.  However, as mentioned in the previous section, this
would require moving the sample region closer to the prime objec-
tive since this objective's size cannot be increased by the  rough
factor of two required and still allow the FPSSS head to fit
in standard 4 in. stack ports.  Our wind tunnel results do not
preclude moving the sample region closer but it obviously will
not be as aerodynamically clean as it currently is.  in view
of the highly turbulent conditions observed in the Valmont stack
clean aerodynamics may not be a profitable design feature and   '
movement of the sample volume closer could indeed be a  better
choice.  A decision to move the sample region closer must also
await tests of a purge air fitting for the window which will
cause some reduction in available room.

     The current instrument design can handle concentrations
up to 50,000/cm3 although coincidence losses must be corrected
for.  An increase in magnification from 20 to 30X will  nrovidA
measurements up to a maximum concentration of 105/cm3 ---

                               188

-------
   105n
  10*-
   103-
n    _.
 I  io2
   10°
  10'1
                                          DIAMETER,
           Figure 14.   Average in-stack size distribution.  The higher resolution data
                       for size range no.  3 has been summed into 0.1 IJJTJ size classes.
                                             189

-------
  105-
            h
  io3-
o
>
  1Q2J
  101
                       M ! n-h
                                   3         4
                                  DIAMETER, u,
  Figure 15.   Average in-stack extinction cross section distribution.  The
              higher resolution data for size range no.  3 has been summed
              into 0.1 \im size classes.   The mean cross section size is  0.79
                                      190

-------
design goal.  An  increase  in the inner collecting angle from
2 to 4° also doubles  the maximum concentration where measure-
ments can be made.  Halving  the laser beam diameter has a four-
fold effect.

     We previously  mentioned that achieving a higher maximum
concentration limit and greater sensitivity were strongly coupled.
First, from glancing  at Figure 14 it is obvious that increasing
the sensitivity automatically increases the number of particles
viewed and coincidence losses.  Conversely, doubling the inner
collecting angle  reduces  the light collected.  The overall sensi-
tivity is obviously reduced  as well but there is a more subtle
effect.  The 2° inner angle  allows for very accurate measurements
out to 10 ym by collecting the diffracted light at small forward
scattering angles.  A deterioration in sizing performance would
result if the inner angle  were increased above 6° for 10 ym par-
ticles or above 10° for 5  ym particles.  Of course, the latter
would require enlarging the  outer collecting angle to achieve
adequate sensitivity. Halving the laser beam diameter aids sensi-
tivity as well as maximum  concentration limits.  However, here
one must be absolutely sure  that alignment will be extremely
stable.  To decrease  the  beam diameter a factor of two requires
either a condensing mirror of half the radius of the current
one or doubling the laser  beam diameter input.


     Probably the easiest  and least controversial change would
be to increase the  magnification to 30X.   The only penalty paid
is in increasing  the  detector bandwidth (admitting more noise)
to see the relatively shorter pulses which would result.   An
increase in bandwidth is required because the photodiode is sized
to view the full  transit of  a particle and any increase in magni-
fication will truncate the time a particle is viewed.

     Work obviously needs  to be done in all of the above areas
to determine optimum  design;  however, progress is complicated
by the impact of  changes  in  one area of design or another.   Con-
versely, other areas  of continuing work should experience rapid
progress.  The DAS  design  should be ready for fabrication in
July, 1978.  From our field  experience with actual stack measure-
ments valuable insight into  desired packaging improvements af-
fording better portability and human engineering have been found.
For instance, we  have found  that five foot boom sections could
pose a problem when catwalks are narrow and guard rails inter-
fere.  Four or even three  foot boom sections may be preferable.
Anyone who has tried  to make measurements around stacks knows
of the difficulties that can occur.  In designing the FPSSS we
have tried to remain  fully cognizant of the user's environment
and attempted to  maximize  .the usefulness of such an instrument.
The real utility  of a device such as the FPSSS is not in extend-
ing its sensitivity to the smallest particles or its ability
to handle the highest concentrations, rather it is in providing


                                191

-------
  105'
                                  TOTAL PARTICLE VOLUME:  7.3 mm3/m3
   10*-
            fl
 E

M

 O
CO"

 Il03-

 LU
    10H
     10'
                                     3         4

                                 DIAMETER, |iim
         Figure 16.   Average in-stack volume (mass) distribution.  The higher
                     resolution data for size range no.  3 has been summed into
                     0.1 pm size classes.  The mean volume (mass) size is
                     1.31
                                         192

-------
  14,000^
  12,000-J
  10,000-j
                                                    SIZE RANGE NO. 3

                                                    0.03/Jm PER SIZE CLASS
   8,000-
 O
«r
O
   6,000-1
   4,000-1
   2,000]
0.4        0.5
                                —r
                                0.6
     0.7

DIAMETER,
                                                 0.8
                             0.9         1-0
             Figure 17.   Average in-stack volume (mass) distribution from 0.4

                         to 0.85 nm.
                                          193

-------
measurements of sufficient spectral quality to gain  insight  into
processes which produce changes in particle size and number  den-
sity while retaining a reasonable confidence in integrated proper-
ties such as mass loading and opacity.

     One final remark is directed at the measurements  reported
in the section on results, above.  We reported that  the  velocity
variations were quite large.  For the FPSSS this poses little
problem; however, it clearly must be problematic for direct  sam-
plers using so-called isokinetic intakes.  In our view it would
be impossible to follow the fluctuations observed with a pumping
system and achieve isokinetic sampling conditions.  What effect
the stack gustiness has on such techniques is not currently  known
but could possibly be explored by intercomparisons with  the  FPSSS.

ACKNOWLEDGEMENT

     This work was funded by the Environmental Protection Agency
 (EPA), IERL—Process Measurement Branch.


REFERENCES

1.   Knollenberg, R.G., J. Hansen, B. Ragent, J. Martonchik,
     and M. Tomasko.  The Clouds of Venus.  Space Sci. Rev.
     20:329-354, 1977.

2.   Colin, L.  The Exploration of Venus.  Space Sci. Rev.
     20:249-258, 1977.

3.   Knollenberg, R.G-, and R.E. Luehr.  Open Cavity Laser "Active"
     Scattering Particle Spectrometry from 0.05 to 5 Microns.
     In: Fine Particles, B.Y.H. Liu, ed.  Academic Press, New
     York, 1976.  pp. 669-696.

4.   Knollenberg, R.G.  Three New Instruments for Cloud  Physics
     Measurements:  The 2D Spectrometer, The Forward Scattering
     Spectrometer Probe, and The Active Scattering Aerosol Spec-
     trometer.  Presented at The Cloud Physics Conference July
     26-August 6, 1976.  Preprint available from the American
     Meteorological Society.

5.   Knollenberg, R.G.  The Use of Low Power Lasers  in Particle
     Size Spectrometry.  SPIE, Practical Applications of Low
     Power Lasers, Vol. 92, 1976.  pp 137-152.
                               194

-------
                              PAPER 9
             OPTICAL MEASUREMENTS OF PARTICULATE SIZE
                  IN STATIONARY SOURCE EMISSIONS
                          A.L.  WERTHEIMER
                           M.N. TRAINER
                             W.H.  HART
                     LEEDS & NORTHRUP COMPANY
ABSTRACT
     A new light scattering  instrument  is described for  in-situ
measurements of particulates  in  the 0.1  to  10.0 ym diameter size
range.  Two modes of scattering  are used, each with two  wave-
lengths of light, to generate  five size  fractions by volume from
a distribution of particulates.  One mode measures polarized
light scattered in two orthogonal orientations at an angle of
90° to the optical probe beam.   The second  mode measures light
scattered in near forward angles  (4 to  11°).  Both modes allow
the extraction of size data  when particles  of different  sizes
are present simultaneously in  the sensing region.  These prin-
ciples have been incorporated  into a prototype portable  stack
monitor, consisting of a 1.5 meter long, 9  cm diameter insertable
probe capable of withstanding  temperatures  up to  260°C.  The
optical signals are carried  through fiber optic cables contained
in the probe.  An arc source  and silicon photodetectors  are
outside the stack at the end  of  the probe,  while  a digital micro-
processor analyzes the set of  measurements  and calculates the
size fractions.  The microprocessor, an  air purge system, the
lamp power supply, and a digital printer are housed separately
from the probe for ease of installation  and service.

INTRODUCTION

     Light scattering is ideally suited  for measurements of par-
ticulates in real time situations.  The  characteristics  of the
materials are not disturbed  during the  course of  the measure-
ments, measured sizes can be  correlated  well with standard opti-
cal microscopy, and the technique is rapid  and,  in general, real
time.  Frequently it is of interest to  measure the mass  or volume


                               195

-------
of particulates within a given  size  interval,  and  recent develop-
ments have produced low angle forward  light  scattering  industrial
process instruments capable of  real  time measurements of particle
size and volume in either liquid or  gases  in the  2 to 200 ym
diameter range.1'2  These instruments  are  also unique for their
ability to simultaneously accommodate  multiple sizes of particles
in the sensing region, so the loading  level  is considerably
higher than  is normally possible with  single particle counters.

     One of the limitations in low angle forward scattering  is
the difficulty in discriminating sizes much  below  the 1  ym  level
with visible light.   Prior to this work no comparable instrumenta-
tion was available to discriminate mass fractions  in  the  0.1
to 1 ym size range,  the lower decade of the  respirable  region.
This paper discusses a new approach, based on  scattering  of  light
at 90° to the direction of an optical probe  beam for  the  genera-
tion of volumetric size fractions below the  range  normally  covered
by forward light scattering.  A combination  of 90° and  forward
light scattering has been incorporated to construct  a prototype
stack monitor capable of measuring volume in five  logarithmically
spaced size  intervals in the range of 0.1 to 10 ym.

PRINCIPLES OF OPERATION

     Light scattering is classically divided into  regions of
analysis according to the relationship between size  of  the  par-
ticle and the wavelength of light.  For particles  much  larger
than the wavelength, scalar diffraction theory is  adequate  to
describe the interaction and define the angular distribution
of scattered light.3  Low angle forward light  scattering  is
commonly discussed using this analysis.

     For particles much smaller than the wavelength,  the  angular
light distribution is independent of particle  size.   Equal  amounts
of light are scattered into forward and backward lobes.    This
is referred  to as Rayleigh scattering,1* and  is typical  of scatter-
ing observed in the atmosphere or from suspensions of low and
intermediate molecular weight materials.

     The most complicated analysis is  required when  the  particle
is comparable in size to the wavelength.  A  full treatment  for
all size ranges was first performed by Mie,5 and entire  texts
have been written using this theoretical approach.6   The  90°
scattering approach described here is  based  on characteristics
of the transition between simple Rayleigh and  rigorous  Mie  scat-
tering, and  the analysis is included in the  next section.

Principles of 90° Scattering

     Mie theory will be used throughout this paper to describe
the angular  distributions of flux for  particles of different
sizes.  Tables7 and computer programs8 are available to facili
tate rapid analysis using Mie theory,  thus eliminating  the  need

                               196

-------
to decide if a simpler  theoretical  treatment would be sufficiently
accurate for the particular  size  and  refractive index of  interest.
Spherical shapes are  usually assumed  in light scattering  theory
and have been used  for  ease  of  computation.

     To illustrate  some specific  characteristics of light scat-
tering, Figures 1 and 2 were computed for  spherical water drop-
lets of refractive  index 1.33.  A dimensionless size parameter,
a, is frequently used where

                              a = TTD/A,                        (1)

with X the wavelength of light.   Figures 1  and 2 cover  a  range
of a = 0.5 to a = 40.   Two orthogonal polarizations of  incident
light are shown, referred to as ix  and i2.   The electric  field
of ix is in a plane perpendicular to  the plane containing the
probe beam and the  observation  point.   The  log of the flux per
particle is graphed,  covering a hemisphere  from 0° (light re-
turning directly toward the  source)  through  180° (forward scat-
tering direction).

     For a = 0.5 and  1.0, Rayleigh  scattering characteristics
dominate.  Equal intensities are  shown in  both forward  and re-
verse directions, and no light  is scattered  at 90° for  the inci-
dent light designated as i2. As  the  parameter, a, increases,
the null at 90° disappears and  the  two curves tend to be  more
alike.  For larger  values of a, the fine structure of the curves
changes slightly as the refractive  index varies.  However, one
of the more stable  characteristics  of the  patterns is the null
at 90° for small values of "a"  with i2, the  light polarized  so
that the electric field is in the plane defined by the  direction
of propagation of the incident  beam and the  point of observation.

     Finally, it should be mentioned  that  these curves  describe
the light scattered from the individual particles.  Suspensions
of N identical particles widely separated  from each other produce
an angular pattern  N  times as intense as that of the single  par-
ticle, if no significant shadowing  or secondary scattering occurs.
This assumption is  referred  to  as single scattering.

     For small "a"  values the differences  between Figures 1  and
2 are greatest in the region of 90°.   The  relative differences
become smaller as the size parameter  increases, where the dif-
ference in intensity  can be  calculated by subtracting the two
curves at 90°.  At  this point,  it is appropriate to consider
the scattered flux  per unit  volume, since  typical particle size
distribution curves frequently  imply a vastly greater number
of small particles  than large ones.  When the flux difference
per particle, ii -  i2/  is divided by  the volume of the  particle,
and plotted against the log  of  "a", a well-defined peak is ob-
served.  Figure 3 shows such a  curve, computed for spheres of
                                197

-------
4-p
                      60        90        120       150

                    ANGLE OF OBSERVATION, degrees
                                                                  1.0
                                                                 0.5
180
  Figure 1.  Log of scattered intensity per particle as a  function of
            observation angle, with forward direction at 180°.  Two
            orthogonal polarizations of incident light are shown, i\
            in Figure 1, and /2 in Figure  2.
                                 198

-------
4 -r
3 -•
            30         60        90        120        150

                  ANGLE OF OBSERVATION, degrees
180,
 Figure 2. Log of scattered intensity per particle as a function of
          observation angle, with forward direction at  180°.  Two
          orthogonal polarizations of incident light are shown, i\
          in Figure 1, and /2 in  Figure 2.
                                199

-------
index 1.33.  In order to simulate a realistic observation  angle,
the flux difference per unit was computed over  an  angular  collec-
tion range of 90° ± 10°.

     The curve in Figure 3 has a peak at about  a =  1.5,  and  the
width at half maximum covers a range from approximately  a  =  1
to 2.  in order to identify a corresponding particle  size, a
wavelength must be specified.  For a helium-neon laser with
X = 0.6328 ym, the half width covers diameters  from 0.2  to 0.4
ym, and the peak is located at 0.3 ym.  Other wavelengths  can
be used to measure volume components at other locations, as  shown
in Table 1.
            TABLE 1.  VOLUME RESPONSE AS A FUNCTION OF
                  WAVELENGTH  FOR 90° SCATTERING

Wavelength, i_im
0.45
0.6328
0.90
Particle diameter
at peak of response, ym
0.21
0.30
0.43
Diameter
range, ym
0.14 to 0.3
0.2 to 0.4
0.3 to 0.6

     These numbers are computed for an index of 1.33.  Other
indices produce slightly different curves, although the basic
characteristics are preserved.  The curve for glass spheres,
for example  (n = 1.55) has its peak at approximately the same
value  (a = 1.5) and is quite similar in shape to the curve in
Figure 3 for the region around a = 1.5.

     The approach, then, is quite simple.  Scattered light in-
tensities are measured for two orthogonal planes of monochromatic
polarized light, at 90° to the probe beam, and the difference
is proportional to the volume of particles in the size range
where a = 1.5.  This value of "a" translates to a size diameter
of approximately one half the wavelength of the probe beam, and
other size fractions can be defined by using other wavelengths.
For the probe described here wavelengths of 0.45 and 0.9 ym were
used to generate two submicron channels.

Principles of Forward Scattering

     Forward scattering has been discussed in references 1-3,
so only a summary of the techniques and pertinent variations'
is included here.  Low angle forward scattering is most readily
treated by using simple diffraction theory.  Three discrete scat-
tered flux measurements are made at observation angles of approxi-
mately 4, 8, and 11 degrees in two wavelengths, 0.45 and 0.90

                               200

-------
ym.  The signals are then algebraically combined  to  produce  a
response per unit volume of material maximized  for particles
at a particular size or size range and minimized  or  reduced  to
zero for particles far from the size of interest.  Since  large
particle scattered flux is concentrated more  toward  the forward
angles, the largest particle response curves  are  dominated by
flux from the innermost zones.  Smaller particles require higher
contributions from the outer zones.  The  nominal  size  range  peaks
for the three forward scattering channels  are listed in Table 2.

               TABLE  2.  FORWARD SCATTERING CHANNELS

Response peak

ym diameter, nominal
1.0
3.5
7.0
Wavelength,
0.90
0.45
0.90
urn


     After the response shape was defined  through scalar diffrac-
tion theory, which does not depend on the  refractive  index of
the material, the design was tested using  rigorous  (Mie) theory.
As expected, the two upper channels where  the respective size
ranges are somewhat larger than  the wavelength of the  light
showed very little shape variation sensitivity to refractive
index of the material.  The most sensitive peak was in the 1
ym range, with the diameter and wavelength nearly equal.  Mie
calculations for all five response curves  used in the  instrument
are shown in Figure 4.  These were calculated for an  index of
1.5, typical of silica particulates, a common stack material.
The ripples in the forward scattering curves occur due to reso-
nances of light in the non-absorbing  (n  =  1.5 - O.Oi)  material,
but will tend to be smoothed if  small amounts of absorption are
present or if the light is not perfectly monochromatic.

EXPERIMENTAL VERIFICATION

     The performance of the volumetric response functions in
the forward channels is based on knowledge and experience with
the Leeds & Northrup Microtrac™  Particle Size Analyzer.  The
use of forward scattering, here, is merely an engineering exten-
sion of a previously tested system, so no  fundamental  testing
was required.

     Major effort, however, was  put into verification  of the
90° response curves.  Since the  response function requires ac-
curate knowledge of signal differences,  variations  in  beam in-
tensity had to be compensated.   A ratio  of ii/I0 ^nd  ia/Io was
measured, where I0 was the strength of the probe beam. Then
the intensity difference was computed.

                               201

-------
                              a a
7Td\
X  /
FigureS.  Intensity difference per unit volume, (ii-i2)/a3, fora
          scattering angle of 90°.  The size parameter, a,  is plotted
          in equal log intervals.
                                202

-------
UJ
CO
Z
O
a.
CO
UJ
cc
ill
O
>
   100% -
80% -
60% -
    40% -
    20%
       0.10
                                                             10.0
                            PARTICLE DIAMETER,
         Figure 4.  Volumetric response curves, as a function of particle diameter,
                for the five channels of the prototype. Curves 1 and 2 are obtained
                with 90° scattering, and curves 3, 4, and 5 from forward scattering.

      An  experimental system was  built,  incorporating a  lock-in
amplifier  and  an electronic ratio circuit, to accurately  measure
90°  scattering.  This system  recorded  scattering curves for  both
polarizations,  ix  and i2, concurrently.  Hence, the response
curve for  the  function  (i1 -  i2)  could  be generated quite easily
and  accurately.

      The system,  shown in Figure  5,  consisted of a xenon  arc,
grating monochromator, and two silicon  detectors.  The  source
flux  was chopped and a lock-in amplifier  used to filter ambient
radiation  noise from the relatively  small 90° scattering  signal.
The  flux passing directly through  the sample was focused  onto
a reference  detector.  This signal was  electronically filtered
to present a dc level to an analog divider, which ratioed the
scattered  and  reference signals  to correct for variations in
source intensity.   Therefore,  the  output  of the divider was
directly proportional to ii or i2.   While a rotating prism polari-
zer  alternately selected i^ or i2, a synchronous motor  scanned
the monochromator  from 400 nm  to  800 nm at a speed chosen so
that  a pair  of  measurements,  ^  and  i2, were recorded once every
5 mm  on a  chart recorder.  Variations  in  the size parameter,
a, were thus accomplished by changing wavelength rather than
size.  Since the volume of particles remained the same, the  flux
per  unit volume was readily determined.
                                203

-------
                                          OP AMP
                                     ROTATING
                                     G LAN-THOMPSON
                                     POLARIZER
                                                           DETECTOR
                                         XENON ARC'
                                         SOURCE
Figure 5. Schematic drawing of laboratory system used to verify the
         volumetric response functions for 90° scattering.
                             204

-------
     This system was used to record data  for  0.234  ym  and  0.801
ym polystyrene spheres, dispersed in deionized water at  20  ppm.
The relative refractive index of polystyrene  to water  was  1.20.
These two particle sizes generated scattering data  for "a"  values
from 1.22 to 2.44 and 4.18 to 8.37, respectively.   The angular
scattering field was 20° centered at 90°  with respect  to the
incident beam.

     Further theoretical Mie scattering studies indicated  that
particle absorption should reduce the secondary volume response
peaks significantly, but cause negligible changes in the primary
response peak.  Experiments were then performed to  confirm  this
selective reduction of secondary response peaks.  Data at  90°
scattering was recorded for dyed (absorbing)  polystyrene spheres
of 0.234 ym and 0.801 ym diameter.  This  data is plotted along
with a theoretical curve for non-absorbing  particles in  Figure
6.  The primary peak data  (d = 0.234 ym)  for  absorbing and  non-
absorbing particles are almost identical, but the secondary re-
sponse peaks  (d = 0.801 ym) are greatly reduced for absorbing
particles.  Notice the excellent agreement  between  experiment
and theory for non-absorbing particles.   These experiments  con-
firmed the theoretically generated response curves, and  gave
us confidence to proceed with the design  of the prototype  in-
strument.

DESIGN OF THE PROTOTYPE

     Real time measurements inside an industrial stack create
rather unique structural and environmental  operation conditions,
with typical temperatures as high as 260°C, flow velocities up
to 50 feet per second, and atmospheres containing acid vapors.
Access to the measuring point is often limited to 10 cm  diameter
ports, and sampling requirements make penetration well into the
stack a highly desirable goal.  Anticipated loading levels  are
in the range of 4 to 40 parts per billion by  volume, assuming
a specific gravity of 2.5 for stack particulates.   For represen-
tative sampling, a sensing zone containing  a  reasonably  large
volume is required.  The prototype design is  based  on  these con-
straints, and Figure 7 shows a sketch of  the  instrument  with
the associated electronics.

Optical Design

     The interior stack temperatures rule out the use  of in-situ
detectors, so a set of high temperature fiber optic cables  is
utilized to sense the scattered light at  five points (three for-
ward angles and two orthogonal positions  at 90° to  the probe
beam).  These cables are installed inside a 1.5 meter  long  stain-
less steel tube, whose outside dimension  is approximately  9 cm.
The active sensing region is towards the  end  of the probe  and
is a slot 36 cm long by 3 cm wide.  A lens  located  in  the  tube
tip collects scattered flux for the forward angles, while  the


                               205

-------
O
CO
    1.0 -
    0.8
     0.6
NON-ABSORBING (EXP)
ABSORBING (EXP)
THEORY FOR NON-
ABSORBING SPHERES
co    04
LU    "••»
EC
     0.2
                123456

                                   SIZE PARAMETER, a

            Figure 6. Theoretical and experimental curves for 90° scattering showing
                     the flux difference, i\  - i2, per unit volume of material.  Two
                     sizes of polystyrene spheres were used, 0.234 and 0.801 ju/n
                     in diameter, and the wavelength  was varied to change the size
                     parameter, a.
                    10
                                                 TRANSCEIVER
                                                 PROBE
                                                                    PRINTER
                                                                          STACK GAS
                 CONTROL
                 CONSOLE
             Figure 7. Prototype system in use in stack, showing control console
                      and printer with transceiver.
                                           206

-------
two 90° fibers look directly through protective  windows  into
the sample region.  Each fiber cable runs  to  its own  detector,
located outside the stack at the end of  the probe.  A sixth  de-
tector is used to monitor beam strength.

     The optical probe beam is generated by a xenon arc  source,
located in the transceiver end of  the probe.   Thin film  inter-
ference filters with center wavelengths  of 0.45  and 0.90  ym  are
combined with linear polarizers in  a filter wheel.  The  light
is then projected down the center  of the tube in a nearly col-
limated beam of alternating blue or infrared  polarized light,
with a beam diameter of approximately 1.25 cm at the  end.  To
avoid spurious signals the light is not  reflected internally,
but exits the probe through a hole  at the  tip.

Electrical Design

     A digital electronic approach  has been taken, similar to
the single detector Microtrac system as  described in  Reference
2.  For this system the six detectors generate electrical signals
in proportion to  the light flux levels incident  on them,  and
after a pre-amplification stage, the electrical  signals  are  fed
to an analog-to-digital converter.  The  microcomputer consists
of programmable read-only memories  (PROM), random access  memories
(RAM), and a central processing unit  (CPU).   Program  instruc-
tions are inserted in  the PROM's,  and the  CPU carries out the
instructions.  Interim calculations and  the final results are
stored in the RAM's until the point in the program where  a dis-
play command is given  to the output.

     The cycle time is adjustable, but a full measurement cycle
can be completed in as little as four seconds.   The digital
microprocessor handles twelve resultant input  signals, five
angular scattering signals and one beam strength  signal from
each of the two colors.  The signals are first combined to pro-
duce the volumetric response curves shown in  Figure 4, and then
a matrix decoupling routine is incorporated to remove  most of
the effects of the response curve overlaps.   A resulting  nor-
malized five channel histogram of the volume  distribution  is
displayed on a digital printer.  A mean size  is  also  computed
from the histogram, as well as a number proportional  to the  total
volume of particulates.

Mechanical Design

     All parts of the  insertable section of the  probe, except
for glass fibers and lens and window material, are fabricated
from stainless steel.   The probe is mounted to the transceiver
with an insulating collar to minimize heat transfer.
                               207

-------
     To insure cleanliness of the optical  surfaces  during measure-
ments, and to provide cooling of the  enclosed  arc  lamp,  a port-
able skid-mounted air blower is provided.   Air  is  forced into
the probe portion through a set of  four  tubes  running  from the
transceiver end.  These tubes terminate  as  specially designed
air curtains to flush across the faces of  the  two  90°  windows
on the sides and the forward scattering  lens system at the end
of the probe.

SUMMARY

     This paper has described the principles and design  of a
new light scattering instrument for real time  measurements of
the size of source particulates.  A photograph  of  the  recently
completed prototype is included as Figure  8, and the operational
characteristics of the unit are defined  in  Table 3.  The instru-
ment offers a method for in-stack analysis  of  particulate size
without dilution or extraction of material, and directly produces
a distribution of the particulates by volume fraction.   This
device thus provides a unique and valuable  measurement capability
for analysis and monitoring of particulates in  source  emissions.

                  Figure 8. Photograph of prototype system.
                               208

-------
           TABLE 3.  CHARACTERISTICS OF PROTOTYPE  LIGHT
                       SCATTERING INSTRUMENT
Size range (particle diameter)

Size discrimination



Anticipated loading range
Operational range

Mode of operation



Power requirements

Operational temperature
Speed of measurement sequence
0.1 to 10.0 ym

Five volume fractions with
centers at 0.2, 0.4, 1.0, 3.5,
and 7.0 ym

0.01 to 0.1 grams of material/
meter3 or 4 to 40 parts/billion
by volume (with specific grav-
ity of 2.5)

4 to 400 parts/billion

Low angle forward scattering
and 90° polarization dependent
scattering

115 volts, 60 hertz, 45 amps

Probe portion in stack:  up to
260°C  (500°F)

Transceiver portion and other
electronics outside stack:
0° to 43°C (32° to 110°F)

Integration time selectable
from 4 to 256 seconds
ACKNOWLEDGEMENT

     The development, design, and construction of  the prototype
were funded by the U.S. Environmental Protection Agency,  under
EPA contract 68-02-2447,  "Instrumentation  to Measure Particle
Size in Source Emissions."

REFERENCES

1.   Wertheimer, A.L., and W.L. Wilcock.   Appl. Optics  15:1616,
     1976.

2.   Wertheimer, A.L., et al.  Effective Utilization of Optics
     on Quality Assurance.  SPIE Conference Proc.  129:49,  1977.

3.   Born, M., and E. Wolf.  Principles of Optics,  Pergamon,
     New York, 1959.  Chapter 8.
                               209

-------
4.    Kerker,  M.   The Scattering of Light and Other Electromag-
     netic Radiation, Academic, New York, 1969.  Chapter 1.

5.    Mie, G.   Ann. Phys. 25:377, 1908.

6.    Van de Hulst, H.C.  Light Scattering by Small Particles,
     Wiley, New York, 1957.

7.    National Bureau of Standards.  Tables of Scattering Functions
     for Spherical Particles, Applied Mathematics Series - 4,
     U.S. Govt.  Printing Office, Washington, 1948.

8.    Dave, J.V.   Subroutines for Computing the Parameters of
     the Electromagnetic Radiation Scattered by a Sphere.  Re-
     port No. 320-3237, IBM Scientific Center, Palo Alto, CA,
     1968.
                               210

-------
                             PAPER 10
      STUDIES ON RELATING  PLUME  APPEARANCE  TO EMISSION  RATE
       AND CONTINUOUS  PARTICULATE MASS EMISSION MONITORING
                            K. T. HOOD
                           H. S. OGLESBY
          NATIONAL COUNCIL FOR AIR AND STREAM IMPROVEMENT


INTRODUCTION

     The National Council for Air and Stream Improvement has
participated in several studies  incorporating extensive field
work and data analysis in investigations relating plume appear-
ance to continuous mass monitoring and emission rate.  Emission
sources that have been studied with plume observing panels to
date include kraft recovery  furnaces, power boilers, and a lime
kiln.  The experience and results gained through evaluations
performed at these sources will  be presented in the following
discussion.

     Continuous particulate  monitors have proven to be a valuable
tool in the development of relationships between plume appearance
and particulate concentration.   The utility of these devices
has been greatly enhanced by  the established linearity of their
response to particulate concentration determined through stack
sampling.  A synopsis of the  evaluation of a mass monitor relying
on the principle of laser light  backscattering is offered as
a means of obtaining continuous  particulate concentration data
in terms of grams per actual  cubic meter.

THE RELATIONSHIP OF PARTICULATE  CONCENTRATION AND OBSERVED PLUME
CHARACTERISTICS AT KRAFT RECOVERY FURNACES AND LIME KILNS

     A study was organized by the National Council in  the summer
and fall of 1974 to determine the relationship among continuously
measured light transmission  properties of selected pulp and paper
process flue gases, the gravimetrically determined filterable
particulate concentration and the appearance of the plumes as
judged by certified observers.   The entire results of  this study


                               211

-------
can be found as NCASI Atmospheric Quality Technical Bulletin
No. 82.  This relationship was derived to establish a  scientific
basis for adoption of plume opacity regulations.

     Previous studies reported on in NCASI Atmospheric Quality
Technical Bulletin No. 79 indicated the validity of using  a
transmissometer as a continuous monitor of flue gas particulate
concentration at temperatures above the moisture dew point.
This conclusion was based on the instrument's linear optical
density response to particulate concentration.  The transmissom-
eter enabled the subsequent association of particulate concentra-
tion to observer measured opacity determined through field test-
ing at two kraft recovery furnace sites in addition to the data
developed on a lime kiln source.  The lime kiln and one  of the
kraft recovery furnaces were sites located in the Northwest
United States.  The recovery furnace at this site was  a  non-
direct contact evaporator system.  The other kraft recovery
furnace was located at a Southern site incorporating a direct
contact evaporator.

     The majority of  the observing panel members taking  part
in  the study were technically oriented students complemented
by  regulatory agency  personnel with extensive plume reading ex-
perience.  A transmissometer was used as an intermediate,  and
as  such opacity or optical density values were simultaneously
recorded corresponding to both the observer panel runs and the
particulate sampling  tests.

     The accuracy and reproducibility of observer read opacity
was characterized through data analysis that involved  the  cal-
culation of observations in accordance with EPA Method IX  pro-
cedures.  This entailed the arithmetic average of 25 readings
taken  at 15-second intervals, which encompassed a six-minute
total  time span.  The result was a data base of approximately
1800 EPA Method IX observations from more than 300 observer panel
runs which formed the data base from which to work.  The normal
size of  the observing panel was thus an average of six indivi-
duals  making and  recording plume readings simultaneously.

     An  observer  opacity lower detection limit in terms  of par-
ticulate concentration was a parameter sought for the  non-DCE
kraft  recovery furnace Northwest site.  The transmissometer was
used as  a reference  for the detection level depicted in  Figure
1.  The  dotted lines  in this figure encompass a range  for  the
transmissometer opacity response  (corrected to a ten-foot  path
length)  where  25% to  75% of the observers reported "non-visible"
or  zero  opacity.  Transformation of this range to the  transmis-
someter  calibration  curve represented in Figure 2 provides a
comparison of  the percent of observers reading non-visible at
the stack exit against the EPA Method V particulate concentra-
tion.  The dotted lines in this figure indicate 25%, 50% and 75°
                               212

-------
of the observers reported non-visible  opacity  corresponding  to  par-
ticulate concentration levels of  0.041,  0.034, and  0.027  g/DSCM
(0.018, 0.015 and 0.012 gr/DSCF),  respectively.   The  conclusion
obtained from this exercise was  that below  this  range the ob-
servers did not see a plume, while above  the concentration range
a plume was detected with a great  degree  of regularity.   The
point defined as the observer detection  limit  corresponded to
that level where 50% of the observers  reported zero opacity.
The particulate detection limit  for the  source studied was ap-
proximately 0.034 g/DSCM  (0.015  gr/DSCF).

     The relationship of plume appearance or opacity  (based on
a ten-foot path length) to particulate concentration  for  the
Northwest non-DCE kraft recovery  furnace  site  is  presented in
Figure 3.  The total observer member variation is represented
by the associated prediction intervals.   Single  observer  opacity
is depicted here as a function of  particulate  concentration based
on data generated with clear or  blue sky  background conditions.
Use of the large field collected  data  bank  which  was  analyzed
to derive this relationship indicated  that  single observer read
opacity could vary by ±13% opacity for the  range  of particulate
concentration studied at  the 95%  prediction interval.  The equiva-
lent relationship of observer opacity  to  particulate  concentra-
tion is presented in Figure 4 for  the  Southern site incorporating
dark mountain background  viewing  conditions.   Total observer
variation was also found  to be roughly ±13% opacity over  the
measurement range of particulate  concentration.   The  particulate
concentration that was indicated  for the  20% observer opacity
level  for both of the background  conditions presented from the
two sites was approximately 0.080  g/DSCM (0.035  gr/DSCF).

     Observer opacity depicted as  a linear  function of trans-
missometer opacity is shown in Figures 5  and 6 for  the Northwest
and Southern sites, respectively.  The variation  in the observer
readings when compared to the instrument  was ±10  to 15% opacity
for the measurement range studied.  The  second parameter  denoted
as "B", or particulate concentration,  on  the X-axis was obtained
graphically from transmissometer  calibration curves.   Figures
3 and  4 presented previously incorporate  this  parameter to enable
their  construction through a simple axis  transformation.

     The lime kiln opacity segment of  the NCASI  field study was
conducted in 1974 at a Northwest site.  Two certified observers
were used in the nine test runs  accomplished.  During each test,
which  ran approximately one hour,  each observer  recorded  one
plume  opacity reading per minute or 60 per  test.  Simultaneous
particulate sampling provided a  comparison  of  mass  concentration
to observed opacity.  Two lime kilns each equipped  with a venturi
scrubber operating in excess of  51 cm  (20 in.) of water pressure
drop were routed to a common stack.  The plume was  read a few
                               213

-------
seconds after stack  exit  allowing the moisture  to  dissipate.
The plume diameter was  judged to be about 6  to  8 stack diameters
at the point of observation.   The stack was  1.8 m  (4.5 ft)  in
diameter.

    100-,
     75H

 CO
 a:
 LU
 tf>
 CO
 o
 3?
     25-
MEAN DATA POINTS
                                     10

                           INSTRUMENT, % opacity
             15
           Figure 7. (NW) All data:  relationship between observers reading
                 nonvisible and instrument opacity.

     An  exponential regression was assumed from  theory  to fit
the data with  the  resulting  relationship displayed as Figure
7.  The  small  sample size proved to be a limitation  in  the data
and chiefly  responsible  for  the wide confidence  interval  noted.
Each observing run was characterized for plume type  and back-
ground.   The codes for the plume conditions experienced are in-
cluded  in the  figure for  informative purposes.

     The visibility threshold or the particulate  level  at which
50% of  the observations  were reported as non-visible was  also
determined for the lime  kiln source.  The data indicated  a value
of roughly 0.041  g/DSCM (0.018 gr/DSCF) for the  detection limit
on this  source.  This  was relatively close to the level found
for the  kraft  recovery furnace of 0.034 g/DSCM  (0.015 gr/DSCF).

THE RELATIONSHIP  OF PARTICULATE CONCENTRATION AND OBSERVED PLUME
CHARACTERISTICS AT COMBINATION WOOD AND FOSSIL FUEL-FIRED BOILERS

     Another portion of  NCASI studies concerning  the relationship
of observed  plume  opacity and particulate concentration dealt
with combination  wood  and fossil fuel-fired boiler  sources
                                214

-------
   0.060-1


•6
VI
-a
^
o>


Z  0.045-
IT
I-
Z

O  0.030-


O
O
OBSERVATIONS NON-VISIBLE
                EXTRAPOLATION
                 CONFIDENCE LIMITS 95%
   0.01 5H
 o
 i-
 cc
                            10
                               20
30
           50-r
                                  INSTRUMENT, % opacity


                     Figure 2. (NW):  Detection range for observers.
               OBSERVER PREDICTION

                  LIMITS:     95%
                                                       EXTRAPOLATED
                     0.01       0.02      0.03      0.04      0.05


                           PARTICULATE CONCENTRATION, gr/dscf
                                                  0.06
            Figure 3.  (NW) Clear data (Std):  observer opacity vs. paniculate

                     concentration.
                                         215

-------
         50 T
         40-
       •  30
       re
       a
       o
       DC
       LLJ
       >
       cc
       LLJ
       tn
       CD
       O
20--
          10--
             OBSERVER PREDICTION
               LIMITS:     95%
                 0.02    0.04     0.06     0.08    0.10

                      PARTICULATE CONCENTRATION, gr/dscf
                                         0.12
           Figure 4. (S) Dark data (Std): observed opacity vs. particulate
                  concentration.
The study in  its  entirety  can be found as NCASI Atmospheric
Quality Technical Bulletin No.  85.   The two types of  boilers
investigated  in this  project were a bark and coal combination
boiler located at a Middle Atlantic site and a bark and  oil com-
bination boiler at a  Southeastern United States site.  The com-
parison of predicted  single observer opacity and transmissometer
opacity for the Middle  Atlantic location is shown in  Figure 8
with the 80%  and  95%  confidence intervals.  As noted,  the ob-
servations were accomplished against a generally cloudy  and hazy
background which  contributed to the wide scatter in the  data.
The values ascribed  to  the independent variable labeled  "A" in
the figure are  the particulate concentrations  in grains  per DSCF
obtained from the transmissometer's calibration curve.   To obtain
units of grams per DSCM simply multiply by 2.29.

     The relationship of predicted single observer opacity and
transmissometer opacity for the Southeastern site is  represented
in Figure 9.  The background described as primarily bright blue
sky was judged  to result in less observer variation than the
cloudy and hazy background conditions experienced at  the pre-
viously discussed site.  Observer variability  as denoted by the
95% confidence  interval corresponded to approximately ±10% opacity
for the Southeastern  site as compared to ±22%  opacity at the
                                216

-------
               50-r
               40--
             •o
             a 30- •
             o
             cc
             LLJ
             CO
             O
               20- •
               10- •
                  OBSERVER PREDICTION
                      LIMITS:     95%
                         10       20       30
                          INSTRUMENT, % opacity
40
                       0.0175     0.0304    0.0446     0.0615
                     PARTICULATE CONCENTRATION, gr/dscf


             Figure 5. (NW) Clear data (Std) intermediate for Figure 3.
Middle Atlantic  site over the measurement range studied.  As
in the previous  figure, the independent parameter denoted as
"A" in Figure  9  corresponds to particulate concentration  in grains
per DSCF as  obtained from the transmissometer calibration curve
for this source.

     While the observer variability  is relatively small as de-
picted in Figure 9 underlying the  accuracy of the relationship,
the slope or change in observer  readings was small for large
differences  in transmissometer opacity response.  The field data
collected suggested that observer  reading only increased  by 10%
opacity for  a  transmissometer increase of 45% opacity.  The Middle
Atlantic site  on the other hand  reflected a 35% observer  opacity
increase which corresponded to a 45%  transmissometer  increase.
Particle characteristics and plume background were judged  to
be the chief contributors to such  phenomena.
                                217

-------
          50 T
           40+
           30
         o
         a
         a
         o
         o
         ai
         >  20
         LLJ
         CO
         m
         O
PREDICTION LIMITS:

      95%


      80%
           10 +
                     10       20       30
                       INSTRUMENT, % opacity
                                              40
                    00175    0.0304    0.0446     0.0615
                 PARTICULATE CONCENTRATION, gr/dscf


              Figure 6. (S) Dark data (Std) intermediate for Figure 4.


     Fuel combination was  one variable expressed  by  the  investi-
gators as responsible for  plume appearance changes causing ob-
lllver response  variability.   The  magnitude of the fuel  combina-
tion changes  at  the study  sites was indicated by  the ratio of
steam derived from  the  coal  and bark which varied at the Middle
Atlantic site over  a range encompassing 1.0 to 2.2  (coal/bark).
The ratio for steam derived  from oil to that derived from bark
fuel was found to  vary  at  the Southeastern  site  from 1.2 to 2.9
(oil/bark).

     Particulate characteristic changes produced as  a result
of  fuel  combination variability include particle density and
index of  refraction.  A range of densities  between 2.0 and  4.0
q/cm3 were  judged  by the  investigators as  possible for coal-fired
power plants.  In  this context particle density, or  maybe  it
would be more accurate to say  the  physical size  of the particle,
could have  a pronounced effect on  the  opacity level while  being
relatively  independent of particulate  concentration.  The  parti-
cle index of refraction is another parameter which  affects plume
                                218

-------
opacity but is not necessarily a  function  of  particulate  concen-
tration.  A small change  in  this  value  can lead  to a substantial
shift in plume opacity.

     The appearance or color of the  plume  is  obviously caused
by the nature of the particulate 'matter in the plume.   Particu-
lates emitted from an oil-fired boiler  can be characterized  into
three general types:  black, white and  colored.   The black par-
ticles are judged to be chiefly carbonaceous  material  containing
traces of white and colored  matter.   The white portion of the
particulate is mainly in  the form of irregular crystals or a
grouping of spherical particles containing primarily silicon.
The colored particles usually consist of a large fraction of
metallic elements and sulfur compounds  in  the form of  oxides
and salts.  The coal-fired boiler particulate emissions range
from milk white, yellow,  gray, orange,  and brown to black.   Black
spheres found as particles consist of unburned hydrocarbons  while
a colorless glassy sphere fraction was  judged to have  been burned
more efficiently.  All of the particles contained a limited  quan-
tity of metallic elements.   A sand and  char mixture was deter-
mined as the major constituent of particulate emitted  from bark
boilers.  While the sand  is  essentially ash which proceeds through
the system unchanged, the char is for the  most part satisfactorily
described as unburned carbon whose quantity and  nature is deter-
mined by boiler design and operation.

     The background against  which the various plumes were viewed
was an important factor in plume  opacity judgements made  by  ob-
servers.  The kraft recovery furnace plumes were reported by
the observers at a higher value when viewed against a  dark moun-
tain or a blue sky background as  compared  to  a cloudy  sky.   The
maximum contrast for the  predominately  "white" plume was  the
controlling factor.  The  bark and coal  combination boiler plume
was judged to yield the highest observer response when viewed
against a grey cloud background rather  than dark mountains or
other conditions.  The bark  and oil  combination  boiler plume
was found to be most detectable with grey  clouds or hazy  sky
as background rather than white clouds  or  blue sky.  Plume con-
trast was indicated as the major  criterion to follow for  maximiza-
tion of observer response resulting  in  readings  comparable to
those measured by transmissometers.

FIELD PERFORMANCE OF A LASER LIGHT BACKSCATTERING SOURCE  PAR-
TICULATE MASS MONITOR

     A study was recently completed  by  the NCASI to evaluate
the applicability of the  P-5A laser  light  backscattering  mass
monitor to the measurement of particulate  concentration prior
to and following control  devices.  Kraft recovery furnaces and
a wood-waste fired boiler were the sources used  to determine
the monitor's performance by comparison to transmissometer opti-
cal density and EPA Method V sampling.


                               219

-------
•fi
•O
o
s>
o
o

<
oc
o
o
LLI


5
Z>
O
I-
cc
                       0.430 (% OPACITY)
         CONG. = 0.0038e
          OBSERVING CONDITIONS:
A- GOOD, BLUE

B -SLIGHT HAZE

C - INTERFERENCE

D - HAZE. LOOPING
   /••	UPPER LIMIT OF 95%

       CONFIDENCE INTERVAL
                                          LOWER LIMIT OF 95%

                                          CONFIDENCE INTERVAL
        0   1.0  2.0  3.0  4.0  5.0  6.0  7.0  8.0  9.0  10.0  11.0 12.0


                     OBSERVED % OPACITY
       Figure 7. Paniculate concentration vs. observed opacity.
                              220

-------
     The operating principles  and  theory  of  the laser  monitor
manufactured by Environmental  Systems  Corporation can  be found
in NCASI Atmospheric Quality Technical Bulletin No.  92 and  in
several other publications.  While beyond the  scope  of this paper,
Figure 10 is offered to  illustrate the basic operation of the
instrument's optics head.   Particles passing through the one-
ended beam generated by  this optical complex causes  light scatter
in all directions.  As shown,  the  instrument has been  designed
to allow light to be returned  along small incident angles.   The
light follows a path co-axial  to  the emitted beam to a light
collection lens.  This lens serves to  focus  the light  to a  solid
state detector.  Changes in the  instrument response  due to  com-
ponent aging or temperature variation  in  the LED output power
are compensated for through a  ratio of the signal detector  re-
sponse to a reference signal.   Interference  from ambient light
sources  is minimized through the  use of a specific pulsed fre-
quency.  Care must be taken, however,  to  shield the  receptor
from artificial light  (such as fluorescent)  when adjustments
for zero and span are performed.

     The first site on which the  instrument  was evaluated con-
sisted of emissions following  a  non-DCE kraft  recovery furnace
source equipped with a high efficiency electrostatic precipi-
tator.   A comparison at  this site  of the  laser light monitor
to an LSI RM-4 transmissometer encompassed a 21-day  time
interval during which  368 simultaneously  hourly averages of mea-
surement response were obtained  for each  of  the monitors.  The
transmissometer was chosen for the evaluation  based  on the  demon-
strated  linear instrument response of  optical  density  to gravi-
metrically determined particulate  concentration found  at this
site and in previous studies.  Use of  the transmissometer facili-
tated the compilation of a large  data  bank to  enable the conduct
of more  accurate and meaningful  statistical  analysis.   The  instru-
ment ranges chosen for the transmissometer correspond  to a  full-
scale value of 0.45 optical density while 0.1  g/ACM  was selected
for the  laser light monitor.

     The relationship developed  for the instrument comparison
is depicted in Figure  11 with  the  95%  confidence interval in-
dicated  by the dashed  lines.   The  regression equation  corresponded
to:

     PR AMC
           = 0.00069 + 0.1861  (OPTICAL DENSITY)
 The  standard  deviation  calculated was 0.0018 g/ACM,  which along
 with a  correlation  coefficient of 0.88 projected a minimal
 amount  of  scatter  in  the data over the range studied.   This
 range encompassed  the lower  half of the most sensitive setting
 of the  laser  monitor  with particulate concentration measurements
 which corresponded  to less than 0.229 g/DSCM (0.1 gr/DSCF) .
                                221

-------
         50
         40
       I-
       5
       <
       Q_
       O
       cc
       UJ
       >
       cc
       LLJ
       CO
       00
       O
       Q
       LLJ

       O
       Q
       LU
       CC
       a.
         30-
20
         10
          0.011 0.022 0.034 0.047 0.060  0.074  0.089  0.105  0.122 0.141
                    PARTICULATE CONCENTRATION, gr/dscf

           0     5    10   15   20   25   30   35    40   45
                          INSTRUMENT % OPACITY
             Figure 8. Bark and coal combination boiler. Mainly cloudy
                    and hazy background.
     The second  portion of this study  was carried out  at a DCE
kraft recovery  furnace operated under  computer control.   Evalua-
tion of the  mass monitor was undertaken at two locations with
characteristic  high mass concentrations,  i.e., immediately pre-
ceding and  following the direct contact evaporator.  A laser
light monitor modified with a high  temperature "ceramic" valve
assembly in  the  probe was employed  for the testing  accomplished
at the DCE  entrance location to enable both gravimetric sampling
and short time  interval RM-4 transmissometer comparisons to be
made.  The  laser light monitor was  operated on the  2 g/ACM range
while the 0.9 optical density range was chosen for  the trans-
missometer  which utilized an actual four-inch measurement path
length which was mathematically adjusted to ten  feet.
                                222

-------
             50
          >  40
          Q.
          O
          cc
          111
          cc
          111
          Q
          UJ
          I-
          o
          Q
          ai
          cc
          a.
30-
            10-
             0.
                                    95% CONFIDENCE
                                      LIMITS
20- - —
                                 80% CONFIDENCE
                                   LIMITS
          (A) 0.029  0.039 0.049 0.059  0.071  0.083  0.096

          (B)  0    5   10   15   20   25   30

             (A)  PARTICULATE CONCENTRATION, gr/dscf
             (B)  INSTRUMENT % OPACITY
                                   0.109

                                    35
0.124

 40
0.140

 45
              Figure 9. Bark and oil comb/nation boiler. Mainly bright
                      blue sky background.

     The  calibration curve for  the laser  light  monitor developed
through particulate sampling at  the DCE entrance  location  is
depicted  in Figure  12.   This relationship corresponds to the
following regression equation:

     Laser Monitor  = 0.038 + 0.334 (Particulate Concentration)

with a standard deviation of 0.076 g/ACM  and  a  correlation  co-
efficient of 0.987.

     The  corresponding  statistical analysis for the modified
transmissometer at  this site was also calculated  with a result
similar to that obtained with the mass monitor.  A correlation
coefficient of 0.978 was found  for this analysis.  The recorder
                                 223

-------
  trace  of  the  transmissometer visually possessed more noise  than
  that  for  the  mass monitor,  only a small portion of which might
  actually  be  attributable to actual recovery furnace operation.

       The  mass monitor required essentially no maintenance over
  a  six-week  study time interval.  The transmissometer, on the
  other  hand,  required daily  attention with respect to lens clean-
  ing  and removal of particulate build-up in the slotted pipe used
  to reduce the measurement path length of the instrument.  The
  information  compiled at this site indicated the mass monitor
  would operate satisfactorily in the range of approximately  3.75
  g/ACM (5  gr/DSCF) found directly exiting the recovery furnace.
  In this application the data generated could serve as an aid
  to the operator in maintaining particulate emissions from the
  furnace at a minimum.

       A third phase of the mass monitor evaluation incorporated
  a wood-waste fired spreader stoker power boiler site equipped
  with two-stage multicyclones.  The boiler was reported by the
  mill to be rated at about 500,000 pounds of steam per hour.
  A total of 142 hourly averages for the mass monitor and RM-4
  transmissometer were compared with the resulting statistical
  analysis represented as Figure 13.  The relationship between
  the two monitors was exceptional with a standard deviation of
  0.002 g/ACM and a coefficient of variation of 0.986.  The regres-
  sion equation corresponded to:
       GRAMS
        ACM
= 0.005 + 0.154 (OPTICAL DENSITY)
                                    LIGHT COLLECTION
                                    LENS
              BACKSCATTERED
              BEAM
EMITTED
BEAM
                                                              SIGNAL
                                                              DETECTOR
                       Figure 10.  P-5A optics diagram.

                                 224

-------
            0.04- •
         u
         ^  0.03- •
         o
         o

         o
         I  0.02
         cc
         LLJ
         GO
            0.01-•
                                    UPPER & LOWER 95%
                                    CONFIDENCE LIMITS
                    0.04    0.08    0.12    0.16    0.20
                       TRANSMISSOMETER OPTICAL DENSITY
                            (10 FOOT PATH LENGTH)
0.24
           Figure 11.  Non-DCE kraft recovery furnace relationship between
                   ESC laser light monitor and Lear Siegler transmissometer.
The equation for the statistical relationship determined for
the two  monitors in this  application was  found to be surprisingly
close  to that presented  in  Figure 11 for  the  non-DCE kraft  re-
covery furnace equipped with  an electrostatic precipitator.  This
result addresses the similarity of the two  monitors in their
response to  particulate emissions with obviously different  par-
ticle  characteristics.

SUMMARY

     The relationships developed between  in-stack measured  opacity
and simultaneous opacity  measurements by  trained observers  have
been found  to aid in the  interpretation of  regulations which
assume these opacity measurements to be equivalent.  The relation-
ship between particulate  concentration and  opacity was defined
                                 225

-------
                /    /   ,—» UPPER & LOWER 95%
                            CONFIDENCE LIMITS
             0      1.0     2.0     3.0     4.0     5.0

                     PARTICULATE CONCENTRATION, 9/acm
            Figure 12.  West cyclone entry: ESC P-5A calibration curve.
over a practical range of  particulate  concentrations at the re-
covery furnaces studied.   An  additional  study was completed to
determine the relationship of combination wood and fossil fuel-
fired boiler plume appearance,  or  opacity,  and particulate con-
centration within a spectrum  of existing and developing parti-
culate emission regulations.   The  findings  for the fossil fuel-
fired boiler paralleled  in many respects those made during in-
vestigations at the kraft  recovery furnace.   These include, among
others, a well-defined variability in  observed plume character-
istics by trained observers viewing the  same plume, and the need
to consider this variation if plume appearance is not to be the
controlling feature of comparison  plume  appearance mass emission
rate regulations.  The findings differ in that the relationship
between plume appearance and  particulate concentration is not
as precise for wood and  fossil fuel combination boilers as for
kraft furnaces.  Particle  characteristics were discussed as
forming the probable  cause of the  lower  precision encountered.
                               226

-------
     An evaluation conducted on a  laser  light monitor designed
to measure  particulate concentration  as  contrasted to opacity
monitors which  measure the light transmission changes induced
by changes  in  flue gas particulate  concentration displayed exemp-
lary results.   When monitoring data were compared with simul-
taneously generated opacity monitoring  records on controlled
sources from a  kraft recovery furnace and a wood residue-fired
power boiler the laser monitor was  judged to be equivalent in
quality of  data and performance when  used on sources with par-
ticulate concentrations of about 0.229  g/DSCM (0.1 gr/DSCF) and
less.

     The laser  light monitor was also found to perform satis-
factorily and  unattended at particulate  concentrations of about
3.75 g/ACM   (5 gr/DSCF) found in  the flue gas of a kraft recovery
furnace preceding an electrostatic  precipitator.  This appli-
cation was  judged to be particularly  attractive as a diagnostic
tool for operators in defining reasons  for variability in par-
ticulate generation within recovery furnaces.
       0.100
     §  0.075
     cc
     o
    O  0.050
       0.025
                                           95% CONFIDENCE INTERVAL
                          0.15
0.30
                                                           0.45
                         , TRANSMISSOMETER OPTICAL DENSITY

                              (10 FOOT PATH LENGTH)
             Figure 13.  Relationship between a laser light monitor and
                      transmissometer for a power boiler.
                                227

-------
                             PAPER 11
          A DATA REDUCTION SYSTEM FOR CASCADE  IMPACTORS
                           J.D. MCCAIN
                            G.  CLINARD
                            L.G. FELIX
                            J.  JOHNSON
                    SOUTHERN RESEARCH  INSTITUTE
ABSTRACT
     A computer based data reduction system for cascade impactors
has been developed.  The system utilizes impactor specific calibra-
tion information together with operating conditions and other
pertinent information such as stage weights and sampling duration
to determine particle size distributions in several forms for
individual runs.  A spline technique is applied to fit a curve
to the cumulative size distribution obtained from each individual
impactor run.  These fitted curves have forced continuity in
coordinates and slopes.  Averages of size distributions for mul-
tiple runs are made using the fitted curves to provide inter-
polation values at a consistent set of particle diameters, irrespec-
tive of the diameters at which the data points fall in the original
individual run data sets.  Statistical analyses are performed
to locate and remove outliers from the data being averaged, fol-
lowing which averages, variances, standard deviations, and con-
fidence intervals are calculated.  The averages and statistical
information are available in tabular and graphical form in several
size distribution formats (cumulative mass loading, cumulative
percentage by mass, differential mass, differential number) .
The averaged data are stored in disk files for subsequent mani-
pulation.  Additional programs permit data sets from control
device inlet and outlet measurements to be combined to determine
fractional collection efficiencies and confidence limits of the
calculated efficiencies.  These results are available in graphical
form with a choice of log-probability or log-log presentations
and as tabular output.  The program is set up to handle all com-
mercially available round jet cascade impactors, including common
                               228

-------
modifications, which are  in  current  use  in stack sampling.   Other
round jet impactors can be easily  substituted and slot type im-
pactors could be accommodated  with slight program revision.

INTRODUCTION

         Cascade impactors have gained wide acceptance  as a prac-
tical means of making particle size  distribution measurements.
These devices are regularly  used in  a wide variety of  environ-
ments, ranging from ambient  conditions to flue  gas streams  at
500°C (950°F).  Specially fabricated impactors  can be  used  for
more extreme conditions.

     Because of their usefulness,  the U.S. Environmental Protec-
tion Agency has funded research which has explored the  theoretical
and practical aspects of  impactor  operation.  As part  of this
research, an effort has been made  to design a comprehensive data
reduction system which will  make full use of  cascade impactor
measurements.

     The cascade impactor data reduction  system (CIDRS) described
here is designed to automatically  reduce  data taken with any
one of four commercially  available round  jet  cascade compactors:
The Andersen Mark III Stack  Sampler, the  Brink  Model BMS-11 (as
supplied and with extra stages), the University of Washington
Mark III Source Test Cascade Impactor, and the  Meteorology  Re-
search Incorporated Model 1502 Inertial Cascade Impactor.   Pro-
vision is not made in this system  for reducing  data taken with
slotted jet  impactors.  With modification the computer  programs
can accommodate any round jet  impactor with an  arbitrary number
of stages, and with more  extensive revision,  can be made to
handle data  from slotted  jet impactors.

     The computer programs which comprise this  data reduction
system are written in the FORTRAN  IV language.   The plotting
subroutines  used were written  specifically for  the Digital  Equip-
ment Corporation  (DEC) PDP-15/76 computer, and  these programs
are not compatible with other  plotting systems.  However, these
programs can be used as a guide when revision is made  for use
with another operating system.

     A broad outline of the  program  fundamentals is given here
with sufficient detail for anyone  without a specialized knowledge
of computers to understand the methods and rationale of the pro-
gram.  The program comprises two major blocks.   The first block
treats data  from individual  impactor runs while the second  treats
data from groups of runs, providing  averages, statistical  informa-
tion and fractional penetration  (efficiency)  results.   The  six
mainline programs which make up the  data  reduction  system  are
described in the overall  program flow shown  in  Table  1.
                               229

-------
                      TABLE 1.  PROGRAM FLOW
                   BLOCK  1.   SINGLE RUN ANALYSIS

                   I.   Impactor  Program (MPPROG)

Takes testing conditions and stage weights to produce  stage  DSQ'S,
cumulative and cumulative % mass concentrations  
-------
in several forms.  The run analysis  and  output  presentation  are
accomplished by three main programs, MPPROG,  SPLIN1,  and  GRAPH.
MPPROG and SPLINl perform analysis and manipulation  while GRAPH
is totally devoted to various  forms  of graphical  presentation
of the calculated distributions.  The routines  used  in  GRAPH
are specifically for use on a  PDP-15/76  computer  and  are  not
compatible with most other computers without  modification.   How-
ever, the general structure of GRAPH should serve as  a  useful
base for programming to achieve  similar  graphical output  from
other computing systems.

MPPROG

     In MPPROG, sampling hardware information,  sampling condi-
tions and particulate catch information  are used  to  determine
the effective cut sizes of the various  impactor  stages  and the
concentrations of particles caught on these stages.   The  output
is organized into several tabular forms  and stored on a disk
file for latter use.

Input Data to MPPROG—

     Because individual impactors, even  of  the  same  type,  do
not necessarily have precisely the same  operational  character-
istics, the program calculates stage cut diameters on an  impactor
specific basis.  Hardware data are stored within  the  program
which include, for each impactor  to  be used,  the  number of stages,
the number of jets per stage,  the jet diameters,  the  stage cali-
bration constants, and flow-pressure drop relations  for each
stage.

     Run specific input data  to  MPPROG are  listed in  Table 2.
The maximum particle diameter  must be measured  by microscopic
examination of the particles  collected on the first  stage.   Gas
analysis must be made at the  same time  the  impactor  is  run.

Output from MPPROG--

     Both input information pertaining  to individual  impactor
runs and calculated results are  listed on the line printer.
A sample of output from MPPROG generated to the  line  printer
is shown in Table 3.

     Input information for each  run  is given  in  the  first five
lines of the printout.   {Impactor pressure  drop  in inches of
mercury is calculated within  the program; gas composition is
input as dry fractions and output as wet gas  composition  by  per-
cent.)  The mass collected on  each stage in milligrams  is listed
in the tenth line of the table.
                               231

-------
                  TABLE 2.   INPUT DATA TO MPPROG
      1.  Impactor identification (required to call up hardware
         information)

      2.  Gas composition (C02,  CO,  N2, 02, H20)

      3.  Impactor flow rate (acfm at stack conditions)

      4.  Stack pressure

      5.  Stack temperature

      6.  Gas temperature within impactor

      7.  Duration of sampling

      8.  True density of particles

      9.  Maximum particle diameter present in sample

     10.  Masses of catches by stage


     The mass loading is calculated from the total mass of par-
ticles collected by the impactor and the total gas volume sam-
pled, and it is listed in four different units after the heading
CALC. MASS LOADING.  The units are defined as:

GR/ACF  -  grains per actual cubic foot of gas at stack condi-
           tions of temperature, pressure, and water content.

GR/DSCF -  grains per dry standard cubic foot of gas at engineer-
           ing standard conditions of gas.  Engineering dry stan-
           dard conditions in the English system are defined as
           0% water content, 70°F, and 29.92 inches of mercury.

MG/ACM  -  milligrams per actual cubic meter of gas at stack condi-
           tions of temperature, pressure, and water content.

MG/DNCM -  milligrams per dry normal cubic meter of gas at engineer-
           ing normal conditions of the gas.  Engineering dry
           normal conditions in the metric system are defined
           as 0% water content, 21°C and 760 mm of mercury  (torr)
                              232

-------
                                                         TABLE 3.  SAMPLE CALCULATIONS
M
U)
CO
HYPOTHETICAL ANDFRSF.N
IMPACTOR F.UOW»ATE • O.soo ACFM
IMPACTOW PRtSSUPE nRUf « 0.3 TN, oF HG
ASSUMED PARTICLE DENSITY B 1.35 GH/CU.CM,
GAS COMPOSITION (PERCtNT) C02 s
CALC. MASS LOADING a 8.07UE-03 GH/ACF
IMPACTOP. STAGE
STAGE INDEX NI.JMRFP
050 (MICROMETERS) 10
[ MASS (MILLIGRAMS) o
IMPACTOR TMPERATUHE « aoo.o F • 2oa,a c SAMPLING DURATION • 20,00 CIN
STACK TEMPEHATURE
STACK PRESSURE •
1 ,9U CO »
l.OTaeE-02
31 32
I 2
.72 9,93 6.
,72 O.ao 0.
> ano.o F «
26,5" I.N, OF
0,00
GR/DNCF
S3 3a
3 a
35 a, is
53 0,09
20tt,a C
HG MAX. PARTICLE DIAMETER « 100,0 MICROMETERS
N2 « 76,53 02 • 20, S3 H20 • 1,00
l,BU70Etai MO/ACM 3,3718E + 01 M"0/ONCM
0
LL
1-
D
a.

85 36 37 88 FILTER
5 6 T 8 9
2.21 1.2B 0,67 0,33
0,3a 1,Oa  6,02E'04

          1.21E-03  1.10E-OJ
LU


H


D



U



LL
U.

5
        GEO,  MEAN  DIA,  (MICROMETERS)
                 (NO,
 J,27t+01  !,03EtOl  7.9«EtOn


           7.93E+01  1.7flEt01


                     5,03F*07
          5,15E.»00   3,OaEfOO   1.68E + 00

          3,2aE+00   8.96E+00   3.95E+01


          3.35E*07   a,52E+08   1.18E+10
          9.SOE.OI  4.75E.01   2.36E-01


          2,94f.tOl  8,56f>01   B,«7EtOO


          5.I8EMO  1,13E*10   
-------
     Below the run condition data summary, the  information  per-
tinent to each stage is summarized in columnar  form  in  order
of decreasing particle size from left to right.  Thus,  SI  is
the first stage, S8 is the last stage, and FILTER  is  the back-
up filter.  If a precollector cyclone was used, a  column labeled
CYC would appear to the left of the SI column and  information
relevant to the cyclone would be listed in this column.  Beneath
each impactor stage number is listed the corresponding  stage
index number, which also serves as identification  for the  stage.

     Directly beneath these listings are the effective  stage
cut diameters.  The effective stage cut diameter is  assumed to
be equal to the particle diameter for which the stage collection
efficiency is 50%.  This diameter, D50, is calculated from  an
equation of the form
           so
                                                               (1)
where
D
           5 0
= effective cut size,
           k   =  stage calibration constant,
           5
            y   =  gas viscosity,

            d   =  jet diameter,

           p   =  particle density,

            C   =  Cunningham  slip correction factor,  and

            v   =  jet velocity.

      Because  the particle diameter, D50, enters  the  equation
 for  C,  the solution of  Equation 1  is obtained by an  iterative
 process.   If  the particle density, pp,  is set equal  to the  true
 density of the particles, as  is the case in the  sample output
 in Table 3, the resulting diameter calculated from Equation 1
 is the  Stokes diameter, DS-   If Pp is  set equal  to 1.0 the  result-
 ing  diameter  is the aerodynamic diameter DA as defined by  the
 Task Group on Lung Dynamics.1  If  both  pp and C  are  set  equal
 to 1.0,  the resulting diameter is  the  aerodynamic impaction diam-
 eter, DAI,  as defined by Mercer.2  Unless otherwise  specified,
 MPPROG  will automatically provide  parallel output in terms  of'
 DS and  DA-  Parallel results  in terms  of DS and  DAI  or in  terms
 of DA and DAI are available  if called  for.

     The  stage weights, in units of milligrams as input, are
 likewise  listed for the respective stages on the line labeled
MASS.   The mass loadings from each stage follow and  are  labeled
MG/DNCM/STAGE  (milligrams per dry normal cubic meter per stage)
                               234

-------
     The percentage of the total mass  sampled  contained  in  par-
ticles with diameters smaller  than  a particular  D50  is called
the CUMULATIVE PERCENT OF MASS  SMALLER THAN  D50.   It is  the cumu-
lative percentage of total mass accumulated  in the stage j.

     The cumulative mass loading of particles  smaller  in diameter
than the corresponding D5? is  listed in four different units:
milligrams per actual cubic meter,  milligrams  per  dry  normal
cubic meter, grains per actual  cubic foot, and grains  per dry
normal cubic foot.  Note that  these are the  same  units used for
calculating the total mass loading.  They  represent  both metric
and English units and both stack conditions  and  engineering dry
standard conditions of temperature, pressure,  and  water  content.

     The geometric mean diameter for the particles collected
on each stage is then listed  in micrometers.   The  geometric mean
diameter of a given stage may  be expressed as  the  square root
of the product of the D50 of  the given stage and  the D50 of the
previous stage.  In calculating the geometric  mean diameter of
the first stage  (or cyclone  if  applicable),  the  maximum  particle
diameter is used instead of  the "D50 of the  previous stage."
In calculating the geometric  mean  diameter of  the  filter, one-
half the D50 of the last stage  (stage  eight, here)  is  used  in-
stead of the "D5U of the given  stage."   (There is  no D5a for the
back-up filter since all remaining  particles are  captured by
this filter .)

     Finally, an approximate  differential  particle-size  distribu-
tion is listed as DM/DLOGD,  in  milligrams  per  dry  normal cubic
meter, and  as number concentration, DN/DLOGD,  in  number  of  par-
ticles per  dry normal cubic  meter.

     Differential size distributions may be  derived  two  ways:

     1.  Finite difference methods  may be  used based on  the DSQ'S
          (abscissa) and the  particulate masses on  each stage
          (ordinate).  This technique was used  to generate the
         differential size distribution data in  Table  3.

     2.  Curves may be fitted  to  the cumulative  mass distribution
         from which the differential curves  (slope)  for  each
         test can be calculated.   This method  is preferred  and
         is described in the  following paragraphs.

SPLIN1

     In many, if not most, sampling programs,  a number of impactor
runs will be made.  Frequently, these  runs will be made  using
several impactors,  having different performance characteristics.
The latter  may be true even  if the same type of impactor is used
throughout  a sampling program.  This  behavior  results both  from
manufacturing variations which cause  calibration differences


                                235

-------
and run-to-run variations in sampling rates, which  cause  shifts
in the DSQ'S.  Averaging results from such testing  to  obtain
a representative composite size distribution requires  that  the
distributions be broken down into like size intervals  for all
the runs to be averaged.  The same requirement  for  like size
intervals also holds for using inlet and outlet data from control
device sampling programs to obtain fractional efficiencies.
This requires curves to be fit to the data for  each run to  permit
interpolation to obtain values at common diameters  for all  runs
to be compared or averaged.

     Before making the final selection of the spline technique
for fitting curves to the size distribution data, consideration
was given to a number of alternate fitting methods, and several
of them were tried.  It was concluded that any  attempt to fit
a predetermined functional form  (e.g., log-normal)  to  the data
was generally not proper.  Because the slope of the cumulative
distribution curve, the differential distribution,  is  the re-
quired quantity for calculating fractional efficiencies, con-
sideration was also given to fitting curves to  the  AM/AlogD ap-
proximations of the true differential distribution, which are
estimated directly from the stage loadings and  D50's.  However,
the magnitudes of the steps in D30 are large enough in most im-
pactors as to frequently make AM/AlogD a poor approximation to
dM/dlogD.  Moreover, the boundary conditions are more  difficult
to handle in fitting curves to AM/AlogD than in fitting to  the
cumulative distributions.  It was ultimately concluded, after
many  trial fitting methods were tested, that the best  use was
made  of the  data  if the fitting was done to the cumulative  dis-
tribution curve by means of a spline method.

      SPLIN1  operates by fitting a curve which is continuous in
X and Y and  the first derivative of Y with respect  to  X to  the
cumulative mass concentration size distribution data.  The  result-
ing fitted curve  is similar to that which one would draw through
the data points using a "French curve" or mechanical spline.
This  fitted  curve  invokes no a priori assumptions as to the shape
of the distribution  (e.g., power law or log-normal).   The manner
in which the spline fits are made is described  below.

     Initial attempts at using the spline technique on the set
of points defining the cumulative distribution curve obtained
directly from the DSO'S were not satisfactory.   The difficulty
occurred as a result of the inability of the method to generate
sufficiently rapid changes in curvature when the curve to be
generated was defined by a small number of points.  A satisfactory
fit could be obtained by adding a set of interpolated points
between the original data points of the measured cumulative curve
These points are generated by means of a series of parabolas
through consecutive sets of three adjacent data points of the
original cumulative curve defined by the impactor stage data
                               236

-------
The fitting is done using  log  (concentration)  and  log (particle
diameter) as variables and  begins  with  the  segment containing
the smallest D50 in the data set.

     The sequence of operations  by which  the  interpolated points
are generated is shown in  Figure 1.   A  series  of parabolas are
fit through consecutive sets of  3  data  points  beginning  at the
smallest D50 as shown  in Figures la and Ib.   In this description,
three interpolation points  between each pair  of D50's will be
assumed.  However, the program will accommodate up to 5  interpola-
tion points.  The use  of more  points will improve  the accuracy
of the fitting, but will require more storage  capacity.   The
interpolation points are located along  the  parabolas, between
the lower pair of the  three Dso  points  used to generate  the pa-
rabola.  The interpolated  points are spaced evenly in log diam-
eter between the pair  of original  points.  A  similar process
is used  to generate interpolated points between consecutive pairs
of Dso's up to the segment which terminates at the D50 of the
first collection stage as  illustrated in Figures Ic to le. A
slightly different procedure which will be  described later, is
used for segments which  include  the first collection stage D5o-

     Since the fitting  is  for  a  cumulative  curve,  negative slopes
are not  allowed.  Therefore, a check is made  for negative first
derivatives of the interpolation parabola at  the bounds  of each
segment  within which  the  interpolated points  are to be generated.
If a negative derivative  is found in any segment other than the
first  (the segment including the smallest D50) a straight line
interpolation between  the  segment bounds is used rather  than
parabolic  interpolation.   If a negative first derivative is found
in the first segment  to  be fitted, a fictitious point is generated
and used to form a parabola which has no negative derivatives
in this  segment.  This fictitious point has the same concentra-
tion value as that of  the  first  point on the  cumulative  curve
and has  a  diameter defined by

         _            _ 	(Dso of last stage)2
           fictitious    (D50  of next to last stage)

The interpolated values for  the  segment  between  the  last  two
D50's on the cumulative curve  are  then generated from  the pa-
rabola which passes through  this  fictitious point, and the points
for the last two stages on the cumulative  distribution curve.

     In the region about  the first stage Dso,  three  sets  of inter-
polated points are generated.  The first are generated by parabolic
interpolation using a parabola through DMAX, D50 (stage 1)  and
D50 (stage 2) as was done in the  case  of the previous  segments.
However, in addition to these, two more  points are generated
along the parabola above  the first stage D50-   These additional
points are spaced evenly  in  log  (diameter)  at the same intervals
in log  (diameter) as the  interpolated  points between D50  (stage


                               237

-------
z

Q
CO


1
LLJ
>


<
_l
D



u
          D50(6) DgQlS) D50{4)   D50(3)  D50(2)   D50(1)                    DMAX
                               PARTICLE DIAMETER

           Figure  1a. Cumulative size distribution from raw impactor data.
z

Q

   - FIRST INTERPOLATION

   - PARABOLA
o
               a/
                 INTERPOLATED POINTS
     	'   I  '   |  '  '  ',1 II	r_l	1   I  I | I  I II	.    .   '..in

          D50<6) D50(5) D50(4)  D50(3)  D50(2)  D50(1)                    DMAX


                               PARTICLE DIAMETER

   Figure Ib.  Start of development of interpolated points between first and last Den.
                                      238

-------
z
O
LU
>
D
5
o
SECOND
INTERPOLATION
PARABOLA
                        INTERPOLATED POINTS
                 4-
                    I  I i  i
                                          i  i i  i 111
                                                                   i  i  i 111
                                                                 H-1-
          D50<6> D50<5) D50<4>  D50<3)   D50<2)  ^o'1'                   DMAX
                              PARTICLE DIAMETER
              Figure  1c. Continued generation of interpolated points
o
 D50<5> D50<4>  D50<3>  D50<2'  D50<1>
                         PARTICLE DIAMETER
         Figure  1d. Continued generation of interpolated points

                                239
                                                                    DMAX

-------
5
1
LU
>
<
_l
D

O
                               INTERPOLATED POINTS ON
                               FINAL PARABOLA
                                                        FINAL INTERPOLATION
                                                        PARABOLA
                          oo'
                                                 _LI 1
          '  , '   I   '  ' '."I	,_!	|_-L_L
          D50<6> D50<5> D50<4>  D50<3>  D50<2>  D50<1>
                              PARTICLE DIAMETER
              Figure  1e. Generation of interpolated points on parabola
                       which includes DM AX.
                                                          j	1   I  I  )IM
                                                                     DMAX
5
<
o
CO
GO
D
5
o
                                                                  SLOPE = 0

                                                       HYPERBOLA AND
                                                       HYPERBOLIC
                                                       INTERPOLATION POINTS
                                                       BETWEEN
                                                       D50 (1) and  DMAX
                      I » i i
                                       I   '   ' | I'll
                                                                    -L_L_LJ
                                                                     DMAX
                D50(5) D50(4)  D50(3)   D50(2)  D50(1)
                              PARTICLE DIAMETER
        Figure If.  Generation of interpolated points on hyperbola through
                   D5Q(1) and DMAX
                                     240

-------
1)  and D50  (stage 2) as shown  in  Figure  le.   These points are
used in generating  the final curve  fit  up to the point on the
cumulative distribution curve  defined by the first stage D50.
The third set of points is  illustrated  in Figure If.

     Note that the  cumulative  mass  distribution used  in the illus-
trations of Figure  1 is one  in which a  large step in  concentration
occurs between D50  (stage 1) and  DMAX.   This is typical of a
cumulative curve for a bimodal distribution  in which  one mode
has a median diameter substantially greater  than first stage
D50.  The interpolation parabola  through DMAX, D50 (stage 1 and
D50 (stage 2) does  not properly represent the shape of the true
distribution curve  in this  region.  In  particular, the true curve
must have zero slope at DMAX.   It was empirically determined
that a hyperbolic interpolation equation fit in terms of linear
concentration and linear diameter between DMAX and D50 (stage
1) with the hyperbola asymptotic  to the  total loading at infinite
particle size resulted in acceptable results for the  final spline
fits.  Therefore, a seven point hyperbolic interpolation is used
in addition to the  previously  described  parabolic interpolation
over this segment of the curve.  This hyperbolic interpolation
is illustrated in Figure If.   The use of the two sets of inter-
polated points in the final  interval will be discussed later.

Generation of the Final Spline Fit—

     The original data points, defined  by the Dso's,  together
with the interpolated points just generated, form a set of points
along a continuous  curve  (if one  disregards  the two sets of
points in the final segment) which  has  no negative slopes.  How-
ever, the derivative of the  curve in most cases will  not be con-
tinuous at  the D5o  points.   The spline  fit to be described is
a  smoothing technique which  generates a  series of parabolic seg-
ments that  approximates a continuous curve through the complete
set of points defining the  cumulative distribution.  The segments
to be generated  now will pass  near  or through those points and
will have forced continuity  in both coordinates and first deriva-
tives.  The technique is applied  first  to cover the interval
between the first and last  stage  D50's  and then a second time
to cover the  interval between  the first stage D50 and DMAX.
From this point  on  in the discussion, no distinction  is made
between the original points  defined by  the D50's and  the inter-
polated values located between them.

     The spline  fit is generated  by joining  successive parabolas
at locations  determined by  the x  (or  log diameter) coordinates
of the points which now represent the cumulative distribution
curve  (original  points at the  D50's plus the interpolated points).
These parabolas  have continuity in  slope forced by the fitting
procedure and are generated  in such a  fashion as to pass near
or through  the points on the cumulative distribution  curve.
                               241

-------
     The procedure is illustrated in Figure  2.  The  spline  fit
is begun at the lowest point, 0, on the distribution  curve  (at
the D50 of the last stage).  The parabola used  to generate  the
interpolated points between the last two stages is assumed  to
be the fitted curve up to the first interpolated point.   (Point
1 in Figure 2a.)   This parabola, a, is followed until the x-co-
ordinate at point 1 is reached.  At the point A, located on this
parabola by the X-coordinate of point 1, a new  parabola  is  fitted
as shown in Figure 2b.  This parabola, b, is forced  to pass
through point A with the same slope at A as  the'parabola used
to define point A, and is forced to pass through the  third  point
above point 1 in the set of points defining  the cumulative  curve,
i.e., point 4.  The parabola, b, is followed to the  point defined
by the X-coordinate of point 2, thus locating a point B.  At
B a new parabola is fit with forced slope continuity  with b
passing through the third point ahead of point  2, i.e., point
5, as shown in Figure 2c.  From C this process  is repeated  using
point C and 6 to generate a new parabola, d, and termination  point
D, e, and E, etc., until a termination point at the  D50 of  the
first collection stage is reached.  The last three points ob-
tained by parabolic interpolation are used in generating the
spline fit parabolas up to the first collection stage D50.  The
coefficients of the fitting spline fit parabolas for  the segments
a, b, c, d, . . etc., are saved for future use.  These now  rep-
resent the smoothed curve and will be used henceforth to define
the cumulative curve for that run.

     The final spline fit starts by picking  up  at the point on
the fitting parabola which terminated at the D50 of  the first
stage.  The same procedure as before is followed, except that
the third point ahead determined by the hyperbolic interpolation
is now used for fitting, and the fitting parabolas are followed
to X-coordinates defined by the hyperbolic interpolation points.
The curve generated in this second zone of the  spline fit [i.e.,
between D50  (stage 1) and DMAX) is an extrapolation which has
been found to be reasonably good to diameters equal  to about
2 to 3 times the first stage D50.  By using  the second, third
(as illustrated),  fourth, etc., point ahead in generating the
final parabola segments one can influence the amount of smoothing
provided by the program.

     The cumulative concentration and slope of the cumulative
curve, dm/dlogD,  can be calculated for any arbitrary particle
size by locating  the fitting coefficients for the spline segment
containing that size.   The boundary locations of each  of the
parabolic segments, 0, A, B, C, .  .,  and the fitting  coefficients
for each segment  are stored in a disk file for subsequent use
by other programs (e.g.,  GRAPH, STATIS,  etc.).
                               242

-------
z
Q
u
                                                                          6
                                                                          O
                                                                5
                                                                O
I	I
                                                                  I  l  I I  I
             D5o                                      D50
        (LAST STAGE) XA = X-\                     (LAST-1 STAGE)

                               PARTICLE DIAMETER

     Figure 2a.   Start of the curve fitting procedure.  Cumulative mass loadings
                 derived from stage catches are represented by solid circles.
                 Interpolated values are shown with open  circles.
                                     243

-------
o
2

Q
<
O
V)
V)
h-
<

3
5
                                 I  ll  I  I
                                                J	I
          J	1  JIM
             D50

        (LAST STAGE)
     U50

(LAST-1  STAGE)
                            PARTICLE DIAMETER
    Figure 2b.  Second step in the curve fitting procedure.  Cumulative mass
                loadings derived from stage catches are represented by solid
                circles.  Interpolated values are shown with open circles
                                     244

-------
                                                                        o
                                                                         6
o
z
5
<
O
in
V)
D
5
D
O
                                                          t  I  I  I  I I  I
           D50
       (LAST STAGE)
xb        xc        D50

               (LAST-1 STAGE)

PARTICLE DIAMETER
      Figure 2c.   Third step in the curve fitting procedure.  Cumulative mass
                 loadings derived from stage catches are represented by solid
                 circles.  Interpolated values are shown with open circles.
                                      245

-------
Problems Resulting from Extremely Close Stage  Cut  Diameters (D5o's)—

     When two stages are used on an impactor which  differ  only
slightly in Ds0, the second of the two will collect too  much
material because of the finite slope of real impactor  stage col-
lection characteristics.  The simplest example of  this effect
would be obtained if two identical stages are  used  sequentially.
If that were the case, in an ideal impactor the  second stage
should collect no material; however, because of  the finite slope
of the real stage collection efficiency curve, it  will collect
some particles.  This would lead to the formation  of a step in-
crease (infinite slope) in the cumulative concentration  curve.
The severity of the effect is reduced as the spacing between
the D50's increases but can be sufficiently severe  to  cause
significant errors in the size distribution curves  if  it  is not
properly accounted for.  Calibrations indicate that the  effec-
tive cut diameters, or D50's, at the first two stages  of  several
impactors suffer from this problem.  The program MPPROG,  because
of this, ignores the presence of the second stage  of Andersen,
MRI, and University of Washington impactors in generating  the
cumulative mass concentration curve from which the  fitted  curves
will be made by SPLINl.  This procedure effectively nullifies
the problem.  However, if calibrations of future versions  of
these impactors do not show the small spacing  in D 5 0,  MPPROG
should be modified appropriately so as not to  lose  good  informa-
tion when the curve fits are made.

GRAPH

     Program GRAPH is dedicated entirely to presenting data from
single impactor runs.  The output forms available  on call  are
cumulative mass loading versus Dso, AM/AlogD versus geometric
mean diameter, and AN/AlogD versus geometric mean  diameter  as
calculated in MPPROG.  The latter are available on  Stokes
aerodynamic and aerodynamic impaction diameter bases.  As  an
option, up to ten runs can be superimposed on  a  single plot.
Plots and tabular output of the fitted curves  from  SPLINl  are
also available.  The fitted curves from SPLINl are  plotted  super-
imposed on the data points from MPPROG, but only as single  run
plots.  The plots are all made on log-log grids.

     The tabular output includes cumulative percent mass loading
less than particle diameter generated from the SPLINl  fitted
curves, dM/dlogD versus particle diameter, and dN/dlogD versus
particle diameter generated by differentiation of  the  SPLINl
fitted curves.

ANALYSIS OF GROUPED DATA

STATIS

     STATIS is a program for combining data from multiple  impactor
runs under a common condition.  The program tests data from £
series of runs  (specified by the user)  tor outliers, flags  and

                               246

-------
removes outliers from  the  set,  and  then  provides output in the
form of averaged size  distributions with confidence intervals
as desired in both tabular  and  graphical form.   The program is
set up to provide 50%  confidence  intervals;  nowever,  changes
can be made for the calculation of  other confidence intervals
as desired (e.g., 90%  or 95%).

     The input data to STATIS are the  fitted polynomial segments
generated from MPPROG  by SPLINl which  now define the  cumulative
mass loadings for each run.  The  particle diameter  basis for
averaging  (i.e., aerodynamic, aerodynamic impaction,  Stokes)
is user specified on control cards  used  to execute  STATIS.

     The fitting equations from SPLINl are differentiated at
preselected particle diameters  to obtain the quantity (dM/dlogD.)
where  i refers to particle diameter and  j refers to the sequenc^  ^
number of a particular run in the set  to be averaged.   The values,
at each particle diameter,  D^,  are  subjected to an  outlier analy-
sis based on the deviations of  the  values of dM/dlogD for indivi-
dual runs from the mean for all runs.

     The outlier test  used is that  for the "Upper 5%  Significance
Level".   A curve fitted to the tabular  list of critical values
for excluding an outlier is used  to generate the table.   The
test is based on the quantity
          -  X
              being  greater  than  a critical value,  c ,  which  is
         S                                           n'
 a  function  of  the  number  of  points in the data set.

      X.  =   individual  value

       X  =   mean of  all values

       S  =   standard deviation  of the data set.

      The application of this test requires that  there be three
 or more  runs in the  sequence to be averaged.   This outlier  test
 is repeated after  discarding any outliers already identified,
 provided there are at least  three runs remaining in the set of
 retained points.

      After  discarding outliers, a final average, standard devia-
 tion,  and confidence interval are calculated  for each (dM/dlogDi)
 These values are output on  the  line printer and  are plotted on
 call  by  the user.

      Cumulative size distributions on a mass  basis or percentage
 basis are derived  from  the  averaged dM/dlogD  values by integra-
 tion  of  these  values.  The  choice of integrating the dM/dlogD
 curve rather than  direct  computation of the cumulative averages
 from  the individual  cumulative  distributions  was based on the

                                247

-------
fact that an error in a single stage weight  is propagated  forward
throughout the cumulative curve for all stages subsequent  to
the one on which the error occurred.  This would  cause  substantial
quantities of good data from other stages to be discarded  by
the outlier analysis.  Integration of the averaged  differential
distribution, on the other hand, allows the data  from  the  re-
maining, error free, stages to have their proper  influence on
the averaged cumulative distributions.  These cumulative dis-
tributions are again output in tabular form and,  on call,  in
graphical form.

     The cumulative distributions can be obtained either includ-
ing or excluding particles smaller than 0.25 ym in  diameter.
The option of excluding the particles smaller than  0.25 ym is
made available because of the fact that in a significant percent-
age of sampling situations, impactor back up filter catches can
be dominated by oversize particles because of bounce and/or re-
entrainment.  This results in a filter weight gain  which can
be many times higher than the weight of the fine  particles,  which,
ideally, should be the only material present.  In those cases,
omission of  the material which is nominally smaller than 0.25
um from the  cumulative distributions will make the  result  a much
better representation of the true size distribution.  This,  of
course, is true only when the D50 of the last impactor  stage
is about 0.25 to 0.5 ym as is usually the case with the commer-
cially available impactors.

     Standard deviations and confidence limits for  the  cumulative
distributions are calculated from the approximation that the
variance  (and square of a confidence interval) for  a sum,  A +
B, is given  by the sums of the variances (and squares of the
confidence intervals) for A and B separately, i.e.,

         Variance    „ = variance, + variance^
                 A ~t~ 15           f\           o

and      (confidence interval)^ + Q = (confidence  interval)'
                                                           A
         + (confidence interval)2
                                B

     The averaged differential size distributions generated  by
STATIS are stored in a disk file for use by the programs PENTRA
or PENLOG in calculating control device fractional efficiency
curves.

     Tabular and graphical output from STATIS includes cumulative
mass loading versus diameter, cumulative percentage on a mass
base versus diameter, dM/dlogD versus diameter,  and dN/dlogD
versus diameter.  The graphical presentations are made on  log-
log grids with the exception of the cumulative percentage  plot
which is made on a log-probability grid.  All output forms,  graphi-
cal and tabular, include confidence limits.   The choice of diam-
eter definition used is left to the user.  An index of  runs  which

                               248

-------
were rejected through  the  outlier  analysis before averaging is
also printed.  Rejection at  any  one  particle size does not result
in the run being excluded  at all particle sizes.

Programs PENTRA/PENLOG

     These two programs are  virtually identical and provide
tabular and graphical  output of  control device penetration and/or
efficiency versus  particle size  for  a preselected series of par-
ticle sizes from about 0.25  to 20  ym.  The only difference between
the two programs is  in the form  of the graphical output.  In
the case of PENTRA,  the fractional efficiency curves are pre-
sented on a log-probability  grid while in PENLOG they are presented
on a log-log grid.

     The calculations  are  made from averaged sets of inlet and
outlet data developed  by STATIS.  The user identifies the pair
of averaged data sets  from which the efficiency is to be cal-
culated together with  the  diameter basis required (i.e., Stokes,
aerodynamic, aerodynamic  impaction).  The program retrieves the
appropriate averaged data  sets and calculates the fractional
efficiency as
          efficiency. (%)  = 1
                                (dm/dlogD.)
                                         i'outlet
                                (dm/DlogDi)inlet
x 100
where  i  refers  to  the  i    particle  diameter  in the preselected
diameter  sequence.   Simultaneously,  if  both  the inlet and  out-
let data  sets  included two or  more  runs,  confidence limits are
calculated  based on  a  method described  by Y.  Beers.1*   The  con-
fidence  level  associated  with  the  limits  generated by the  program
as provided are 50%  levels; however,  other levels can be generated
by simply changing values of three  constants used to generate
the appropriate t-table.

Test Cases  and  Exemplary  Results

     Tests  of  the  final  fitting process were made by generating
fictitious  impactor  runs  having known size distributions.   These
runs were generated  by calculating  the  D50's associated with
several  sets of sampling  conditions.   The stage weights required
to produce  exact unimodal and  bimodal log normal distributions
were then generated  for  these  sets  of particle diameters.   The
program  was exercised  on  these artificially constructed runs
and results obtained from the  fitting procedure were then  com-
pared  to  the original  distributions.   Figures 3 and 4 show ex-
amples of two  such tests  in the form of differential size  distri-
butions.  Figure 3 illustrates the  input distribution and  re-
covered  distribution for  an aerosol having a mass median diameter
of 4 ym  and geometric  standard deviation of 3.0.  Recovered dis-
tributions  from the  spline fit and  approximation results,  AM/AlogD,

                                249

-------
    10"
                            t
    103
u
•G
•&

Q
O
o
Q
    102
                                        « UIMIMODAL LOG NORMAL DISTRIBUTION
                                        D DM/DLOGD BASED ON CURVE FITTING
                                        4 AM/ALOGD BASED ON STAGE WEIGHTS
                                          MMD = 4.0 jum; a = 3.0
    101
      10-
10°
                                                                                     102
                                   PARTICLE DIAMETER, ,um
         Figure 3.  Approximate differential size distribution based on stage weights
                  and same distribution based on spline fitting are compared to a true
                  unimodal log normal distribution.
                                         250

-------
u
^

I
cf
O
Q
    10°
   10
    1-1
      10-'
                                                                  10
                                                                    1-1
                                              u

                                              "I


                                              Q"

                                              O

                                              Q
10°                 101

PARTICLE DIAMETER, jum
102
                                         10
                                           r3
                       -•- BIMODAL LOG NORMAL DISTRIBUTION
                       a  dM/dlogD BASED ON CURVE FITTING

                       A  AM/AlogD BASED ON STAGE WEIGHTS

                          MMD'S = 2.0 urn AND 10.0 Mm; a = 1.5
     Figure 4. Approximate differential size distribution based on stage
              weights and same distribution based on spline fitting are
              compared to a true bimodal log normal distribution.
                                   251

-------
taken directly from the stage weights both show excellent  agree-
ment with the input distribution.  The fitted results  for  diam-
eters larger than 7 ym represent an extrapolation  to sizes larger
than the first stage D50.  Figure 4 illustrates a  similar  test
for a bimodal distribution having equal amplitude  modes, mass
median diameters of 2 ym and 10 urn, and geometric  standard devia-
tions of 1.5.  Again, beyond about 7 ym, the fitted points represent
extrapolations.  Note that the AM/AlogD approximations  derived
directly from the stage weights lie very close to  the  input curve
in regions where the slopes are not large but fall significantly
above the true curve in regions of high slope.  Errors  expressed
as percentage deviations from true values are shown for  two cases
each for unimodal HMD = 4, ag = 2, and bimodal MMD = 2,  ag = 1.5,
and MMD = 10, ag = 1.5 distributions in Figures 5  and  6.   Note
that the results from the fitted curves generally  fall  within
±10% or better of the true values in the size interval  covered
by the impactor stage D50's and are for the most part  within
±50% of the  true values in the extrapolation region above  the
first stage  D50.  Much larger errors occur with the AM/AlogD
approximations  to the differential distributions obtained  di-
rectly from  the stage weights.  The errors shown in Figures 5
and 6 result only from the fitting procedure and do not  include
any effects  from non-ideal behavior in the impactors.   Errors
arising from the latter can be much greater, as described  by
McCain and McCormack.5

     Examples of some of the graphical output formats available
from the program are shown in Figures 7 through 10.  Figure  7
illustrates  a single run cumulative mass distribution with  the
original data points and fitted curve from SPLINl.   Figure  8
shows the differential distribution obtained for the run shown
in Figure 7.  Figure 9 illustrates a cumulative mass distribution
on a percentage basis with confidence limits obtained from  the
average of several runs similar to that shown in Figures 7  and
8.  Figure 10  illustrates a control device penetration curve
with confidence limits obtained from sets at averaged inlet  and
outlet runs.

SUMMARY AND  CONCLUSIONS

     CIDRS represents a powerful, versatile tool for reducing
and managing data obtained with cascade impactors.   It provides
the capability  for single and multiple run data analysis with
varying degrees of smoothing of single run data available  and
averaging and statistical analysis of multiple runs.  Results
from the program are not biased by forced fits to  arbitrary
distribution forms.  Finally,.the program makes possible a  very
significant  time saving in handling and processing field data
obtained with cascade impactors.
                               252

-------
                  30
                  20
                  10
ro
Ul
Co
o
O
cc
cc
                -10
                -20
                -30
                    — dM/dlogD BASED ON CURVE FITTING TO AN ANDERSEN RUN
                     A AM/AlogD BASED ON STAGE WEIGHTS OF SAME ANDERSEN RUN
                    ... dM/dlogD BASED ON CURVE FITTING TO A BRINK RUN
                     D AM/AlogD BASED ON STAGE WEIGHTS OF SAME BRINK RUN
                        MMD = 4.0 pm; a = 3.0
                   0.1
1.0
                                                                   10
                                                      PARTICLE DIAMETER, j
                                 Figure 5.  Percent error of approximate differential size distributions
                                          based on stage weights and the same distributions based on
                                          spline fitting from a uni modal log normal distribution.
100

-------
Ln
 70

 60

 50

 40

 30

 20

 10

  0

-10
               o
               g   -20
               DC
               HI
                   -30
              o
              o
                   -40

                   -50

                   -60
                   -70
                     0.1
                     dM/dlogD BASED ON CURVE FITTING TO AN ANDEBfcEN RUN
                  A  AM/AlogD BASED ON STAGE WEIGHTS OF SAME ANDERSEN RUN
                 ...  dM/dlogD BASED ON CURVE FITTING TO A  BRINK RUN
                  D  AM/AlogD BASED ON STAGE WEIGHTS OF SAME BRINK RUN
                     MMD'S = 2.0 urn AND 10.0 jum; a = 1.5
                                           I
                                                                       I
                                1.0
10
                                                                                                               10
                                                        PARTICLE DIAMETER, //m
                                 Figure 6. Percent error of approximate differential size distributions
                                          based on stage  weights and the same distributions based on
                                          spline fitting from a bimodal log normal distribution.

-------
         ICDLO-y i-13-76 1544 POTS 4,5.6
         M) - e»40 QI/CC
    10S:

s
H
a
    I0h:
$
M
   10'
                                 D INPUT DATA
                                 — CURVE FIT
                                                             M
                                                             _J
                                                             LJ
                                                          ,-s
                I  M Ml
I  I I MM|	1—I  I  I HIM
       10'
       PARTICLE  DIA^€:TER  (MICROMETERS)
          Figure 7. Single run cumulative mass distribution with original
                 data points based on stage weights and fitted curve
                 from SPLIN1.
                               255

-------
 101D-37 1-19-76 1544 PORTS

 W = e.4D M/CC
]
m
Iff-.
:
-
101,
10P:
•
icr1-
•
a
•
;
.••
..Q>. • '
cf 'n..ffl a •
• •
•a
: D
: • •
• Q • •
• •
••..
; Q AM/AlogD FROM STAGE WEIGHTS
• dM/dlogD FROM SPLINE FIT
•
	 1 	 1 1 1 lllH 	 1 	 1 1 1 Mill 	 1 	 1 » I I "il
                               lo1

PARTICLE  DIAN€!TER   (MIO30METER5)


   Figure 8. Differential size distribution obtained for the run in
          Figure 7 based on stage weights and based on curve fitting.

                       256

-------
         OOS WOW 1IE5T FOR M0SBU
99.39
3 " ^>3 "3T
OwJ • 3 i
99. Bf
99.5^
994
9B^
95:
goi
.
»
m
*
L
m
w
BOf
70 1 fj
604
50i

4OJ
"3O i
'•- I
\
\ w
r ,«*
: _«
• _•
J3W ~F *
± K
EOf
I ,
••i n j
1U "
si

2 ^
li
o.si
: I
1 I
I
I
[ I
I I
O.Ei
n. n-i T ii — i 1 1 iiu i i i i i im 	 1 — i t 1 1 uu
       icr1          ±cP           lo1
       PARTICLE  DIAMETER  (MICRDNCTER5)
         Figure 9. Cumulative mass distribution on a percentage basis with
                confidence limits obtained from the average of several
                runs similar to that shown in Figures 7 and 8.
                           257

-------
           PE^ETRATIa^l-EFFICIE^CY
cms YBHDI i TCI R» reeiRwm-ffnnBcr. rem»
99.95;
99. B'-
>_ 99.8-
y
Ld
c "-5-
M ;
Li_ 99 "
U
§ ^
e :
95-
•
90;
1C
r— >
_ -
. -
-
. •
• m
. «
. •
_ -
. •
. -
k •
. •
• *
» *
m *
» •
' T I '
• T «L _
!«
I •
T *
• «
- M
! i1 i
i i i 1 1 1 1 1 1 j iiiiuii i 1111111*
T1 10° 101 1C
A r~-»^" T r"*i r~" r"^^ A& ji i i i » <* & J^TI *i M u *• • • • ^
•
:0.05
L0.1
-O.E g
M
•0.5 ^
-1 ^
CJl m
PERCENT
-10
•f
F/5»tv/'e /O.  X\ control device penetration curve with confidence limits
         obtained from sets of averaged inlet and outlet runs.
                        258

-------
ACK NOWLEDG EMEN TS

     This work was conducted  under  U.S.  Environmental Protection
Agency contracts  68-02-0273 and  68-02-2131.   The continued sup-
port and assistance  of Dr. D.B.  Harris,  the  EPA project officer
on these contracts is gratefully acknowledged.   Additional ap-
preciation  is also expressed  to  Mr.  B.  Gaston and Ms. A.  Henry
for their assistance with  the programs;  to Mr.  K. Gushing whose
earlier program was  used  as a basis for  program MPPROG; and Dr.
W.B. Smith  for his assistance and guidance during the program
development.

REFERENCES

  1.  Morrow,  P.E.  Deposition and Retention  Models for Internal
     Dosimetry of the  Human Respiratory Tract.   Health Phys.
     12:173-208,  1966.

  2.  Mercer,  T.T., M.I.  Tillery, and H.Y.  Chow.  Operating Charac-
     teristics of Some  Compressed Air Nebulizers.  J. Amer. Ind.
     Hyg. Assoc.  29 :66-78-, 1968 .

  3.  Quality  Assurance  Handbook  for Air Pollution Measurement
     Systems, Vol.  1.  Principles.  EPA-600/9-76-005, U.S. Environ-
     mental Protection  Agency, Research Triangle Park, NC, 1976.

  4.  Beers, Y.   Introduction  to  the Theory of Error.  2nd Edition,
     Addison-Wesley, Reading, MA, 1957.


  5.  McCain, J.D., and J.E. McCormack.   Non-ideal Behavior in
     Cascade  Impactors.   Paper 77-35.3,  70th Annual Meeting,
     APCA,  Toronto,  1977.
                                259

-------
                             PAPER 12


        AEROSOL GENERATION AND  CALIBRATION  OF  INSTRUMENTS
                          DAVID Y.H. PUI
                         BENJAMIN  Y.H.  LIU
                MECHANICAL  ENGINEERING DEPARTMENT
                      UNIVERSITY OF  MINNESOTA
ABSTRACT

     Standardization and calibration of aerosol measuring in-
struments generally require the use of monodisperse aerosols.
In this paper, a review is first given of various aerosol gener-
ators that can be used for instrument standardization and cali-
bration.  The basic principles of several generators are described
which can be used for producing monodisperse aerosols of primary
standard quality and polydisperse aerosols of high concentration
stability.  Particular attention is devoted to the aerosol genera-
tors developed at the Particle Technology Laboratory, University
of Minnesota; these include the vibrating orifice monodisperse
aerosol generator, the mobility classifier monodisperse aerosol
generator, the ultrafine condensation monodisperse aerosol genera-
tor, and the constant output atomizer aerosol generator.  With
the use of these generators, monodisperse and polydisperse aerosols
can be generated from 0.002 ym to 50 ym in diameter at various
concentration levels up to 106 particles/cm3 in certain size
ranges.  Further, the particle size and concentration from the
monodisperse aerosol generators are known to a high degree of
accuracy  (2% for size and 5% for concentration).  The accuracy
has been verified by using independent microscopic and other
particle sizing and counting techniques.

     In addition, the paper reviews various aerosol measuring
and sampling devices that have been calibrated by means of the
monodisperse aerosol standards.  These include the diffusion
battery, the condensation nuclei counter, the electrical aerosol
analyzer, the optical particle counter and the inertial impac-
tor.  The calibration procedures, precautions, and results are
briefly outlined.  In addition, comparative studies for some
of the calibrated instruments are described.  It  is shown  that
good agreement can be obtained when the instruments are properly
calibrated and standardized.
                               260

-------
INTRODUCTION

     Recent advances in experimental  aerosol  science  and  instru-
ment development have made possible the  rapid,  in  situ  measure-
ment of particle size distribution.   Instruments are  now  avail-
able for size determination of  aerosols  from  0.002 to over  50
ym in diameter.  The successful application of  these  instruments
to experimental aerosol studies requires that the  instrument
be properly standardized and calibrated.   A well-calibrated in-
strument is essential for the correct interpretation  of experi-
mental data, and for obtaining  the highest possible accuracy
from a given device.

     Standardization and calibration  of  aerosol measuring instru-
ments can best be accomplished  by the use of  monodisperse aero-
sols.  The size, and sometimes  the concentration,  of  the  cali-
brating aerosol must also be known to a  sufficiently  high degree
of accuracy.  The quality of the calibration  is often dependent
upon the quality of the calibrating aerosol used and  the  accuracy
to which the particle size and  concentration  are known.  Figure
1 shows the size range of some  of the commonly  used aerosol size
distribution measuring instruments, and  the size range  and  other
pertinent characteristics of the monodisperse aerosol generation
techniques that can be used for instrument calibration.

AEROSOL GENERATION

Monodisperse Aerosol Generation Techniques Available  Before 1970

     Prior to 1970, the most commonly used techniques for generat-
ing monodisperse aerosols for  instrument calibration  and  experi-
mental aerosol studies were the condensation  aerosol  generator
of La Her and Sinclair1 and the several  variations of this gen-
erator as reported by Rapaport  and Weinstock,2  Liu et al.,3 and
others;1* 6 and the spinning disc aerosol generator as originally
reported by Walton and Prewett7 and May,8 and subsequently by
others.9"13 These aerosol generators  are capable of generating
aerosols of a moderate degree  of monodispersity (og - 1.10).
However, both the size and the  concentration  of the aerosol must
be determined by an independent technique, such as electron or
optical microscopy.  Therefore, the accuracy  of the aerosol par-
ticle size and concentration  is limited  by the  accuracy of the
size and concentration measuring techniques used,  which is often
not very high due to the  inherent limitation  of the technique
itself, the tedious nature of  the process involved, or  the re-
quirement of high operator skill.

     A relatively simple  technique of generating  a monodisperse
aerosol of a known size is that based on the  use  of monodisperse
suspensions of polystyrene and  other  latex spheres available
from Dow Diagnostics  (P.O. Box  68511, Indianapolis, IN  46268).
These spheres are prepared by  an emulsion polymerization  process


                                261

-------
                                                              PARTICLE DIAMETER, ;um
                        0.001
                                      0.01
     0.1
                               10
                                                                                                                  100
          AEROSOL
          GENERATION
          GENERATION
          METHOD
                       CONDENSATION-
                       COAGULATION
ELECTROSTATIC
CLASSIFICATION
                    VIBRATING
                    ORIFICE
to
       ag                  ~1.4
Sizing Accuracy                 10%
Concentration Accuracy           10%
Maximum Obtainable
Concentration, particles/cm^       10°
                                                104
                                                              -1.05
                                                                2%
                                                                5%
  106
105
                                   ,1.03
                                     1%
                                     5%
103
         AEROSOL
         INSTRUMENT


         CONTINUOUS
         MEASURING
         DEVICE
                        CONDENSATION NUCLEI COUNTER
                        AND DIFFUSION BATTERY
                                                                           OPTICAL PARTICLE COUNTER
                                          ELECTRICAL AEROSOL ANALYZER
         SAMPLING
         DEVICE
                                                                                  INERTIAL IMPACTOR
                               Figure 1. Size range of aerosol generation, measuring, and sampling
                                        devices.

-------
and are very uniform in size, with ag  generally  less  than  1.06.
Both the size and the ag of the particles  are  determined by  the
manufacturer by electron microscopy.   Although these  particles
are widely used in several applications, for example,  in cali-
brating optical particle counters, there are several  problems
associated with the use of these particles  which  are  worth point-
ing out.

     One problem results from the fact that the  latex  particles
in liquid suspension must be aerosolized,  which  is  usually done
by means of an atomizer.  During the atomization  process, a  large
number of empty water droplets are produced, along  with those
containing the latex spheres.  When these  empty  droplets are
evaporated, residue particles are formed from  the dissolved  im-
purity in the liquid.  The residue particles are  usually orders
of magnitude higher in concentration than  the  primary  latex
spheres  (see Whitby and Liullf; Langer  and  Lieberman15) .  Thus,
the use of the latex aerosol for instrument calibration is limited
to those calibrations for which the presence of  the residue  par-
ticles is unimportant.  For example, the latex aerosol can be
used for calibrating optical particle  counters,  which  generally
do not respond to the residue particles.   However,  it  cannot
be used to calibrate the electrical aerosol analyzer  or the
condensation nuclei counter, both of which  are sensitive to  the
small residue particles present.

     For a detailed discussion of the  various  aerosol  generating
techniques including those described above, the  reader is referred
to the review papers by Fuchs and Sutugin16 and  Raabe.17

Modern Techniques for Generating Monodisperse  Aerosols--
Generation of Monodisperse Aerosol Standards

     A new generation of monodisperse  aerosol  generators has
been developed during the pa'st few years,  primarily as a result
of research at the Particle Technology Laboratory,  University
of Minnesota.  The aim of this research was to develop generators
for producing monodisperse aerosols of a known size and/or con-
centration, which can be used as standards  of  calibration for
aerosol instruments and for general aerosol research.  As a  re-
sult of this research, solid and liquid aerosols  of extremely
narrow size distributions can now be generated.   Further, the
size and concentration of the monodisperse  aerosol  generated
can be calculated to a high degree of  accuracy from the basic
generator operating conditions.  The monodisperse aerosols gen-
erated by these devices can be referred to as  "aerosol standards".
The particle size range and other pertinent characteristics  of
these aerosol generators have been summarized  in  Figure 1, men-
tioned earlier.
                               263

-------
Vibrating Orifice Monodisperse Aerosol  Generator —

     For generating monodisperse aerosols  in  the  size range from
0.5 ym to over 50 ym, a vibrating orifice  monodisperse aerosol
generator has been developed by Berglund and  Liu.     The generator
is based on the instability and uniform break-up  of  a liquid
jet under periodic mechanical disturbance.  The  generator,  shown
schematically in Figure 2, is composed  of  a droplet  generation
and dispersion system and an aerosol dilution, neutralization,
and transport system.

     To generate an aerosol with this system,  the material  to
be aerosolized is first dissolved in a  suitable  solvent,  e.g.,
NaCl in water, or DOP or other oil  in alcohol.   The  solution
is then supplied to the droplet generator  by  a syringe pump.
In the droplet generator, the liquid flows through a small  (5,
10 or 20 ym diameter) orifice, which is vibrated  by  a piezoelec-
tric ceramic.  The liquid jet is broken up by  this vibration
into uniform droplets which are then quickly  dispersed by a
turbulent air jet.  The dispersed droplets are then  mixed with
a much larger volume of filtered dry air to evaporate the solvent
from the solution droplets.  The monodisperse  aerosol formed
is then passed through a vertical drying column  containing  a
radioactive 85j(r source for neutralizing the  particle electro-
static charge.  The monodisperse aerosol is then  ready for  use.

     The diameter, Dp, of the aerosol produced by the vibrat-
ing orifice generator can be calculated from  the  equation
           Dp  =  (6QjiCvAf)                                      (1)

 where  Q^  is the  liquid  solution  flow  rate  through  the  orifice,
 Cv  is  the volumetric  concentration  of  the  non-volatile solute
 in  the solvent,  and  f is  the' vibrating  frequency.   The quantities
 Q^ ,  Cv, and f can  all be  measured accurately.   The overall  un-
 certainty of  the calculated  particle  size  is  about 1%.   Further,
 since  the rate of  droplet production  is  equal  to  the vibrating
 frequency,  the theoretical particle concentration, Nfc^ ,  is  given
 by


           Nth =  f/Qa                                           (2)

 where  f is the vibrating  frequency  and  Qa  is  the  total air  flow
 in  the drying column.  The actual concentration is slightly less
 than the  theoretical  concentration  because of  particle loss in
 the  system.   When  the losses are properly  determined,  the genera-
 tor  can be used  as a  secondary concentration  standard  with  un-
 certainty of  about 5%.  The  operating  conditions  of the generator
 are  summarized in  Table 1.
                               264

-------
                DROPLET GENERATOR DETAIL
                        DISPERSED
               DISPERSION DROPLETS OR|RCE

               ORIFICE  ^
-------
        TABLE 1.   CHARACTERISTICS OF THE VIBRATING ORIFICE MONODISPERSE AEROSOL GENERATOR
                         (MODEL 3050 BERGLUND-LIU  MONODISPERSE AEROSOL GENERATOR,
                              TSI,  INC., P.O.  BOX  3394, ST.  PAUL,  MN 55165)

       Diameter of liquid  Nominal frequency,   Droplet diameter,  Particle diameter,  Nominal concentration,
          orifice, urn            kHz                 yma            range,  ymb          particles/cm3c
               5                450                 15              0.6 - 15                273

^             10                225                 25              1.0 - 25                137
CTl
^             20                 60                 40              1.8 - 40                 36

       a
         Continuously adjustable over an approximate 25% range  by varying the frequency.
       b
         Obtainable by the  solvent evaporation  technique.

         Theoretical concentration based on the nominal aerosol output of 100 liters per minute.

-------
according  to  electrical mobility.   The generator,  shown  schemati-
cally in Figure 3,  consists of  an  atomizer, a diffusion  dryer,
a 85Kr "neutralizer", a differential mobility analyzer,  and an
electrometer  current sensor.
     To generate a monodisperse  aerosol with this  system,  a poly-
disperse  aerosol is first produced by spraying a liquid  solution
with the  atomizer and drying  the particles with the  diffusion
dryer.  The  aerosol is then passed through the 85Kr  "neutralizer"
to obtain a  Boltzmann equilibrium charge on the aerosol  particles,
This aerosol is then classified  electrostatically  by the dif-
ferential mobility analyzer.
                                            2 2
      The  differential mobility  analyzer, described  in  detail
by  Liu  and  Pui20 and by Knutson and Whitby,23  is  in the  form
of  two  concentric metal cylinders.   Aerosol and clean  air  are
introduced  into the apparatus near  the top and flow down the
annular gap space between  the cylinders in the form of laminar
streams.  A dc voltage  is  applied to the inner cylinder—the
collector rod—and the  outer cylinder is grounded.   The  applied
dc  voltage  causes particles of  the  opposite polarity to  be at-
tracted to  the collector rod, and those that have  the  correct
mobility, and hence the particle size, will be attracted to the
                        ROTAMETER

                               COMPRESSED AIR
                                                 DRYER
                                                     ABSOLUTE
                                                     FILTER
             H.V. POWER
             SUPPLY
                D-
 LINEAR
 FLOWMETER
             SILICA
             GEL
        ROTAMETER |
  DILUTION
  DRY AIR
      DIFFERENTIAL
      MOBILITY ANALYZER
      EXCESS
      AIR
r<*3—B—'
  MONODISPERSE
  AEROSOL
      |
-------
vicinity of the slit where they are swept out  by  the  small  air
stream flowing through the slit.  The mean electrical mobility
of the particles extracted by the device, Zp,  can  be  calculated
from the operating conditions and the dimensions  of the  analyzer
by the equation
                q  + -r
                ^/~i   y
                 •'c
V L
where qc is the flow rate of clean sheath  air  in  the  mobility
analyzer, qa is the flow rate of the polydisperse  aerosol  enter-
ing the analyzer, qs is the flow rate of the monodisperse  aerosol
leaving the analyzer, r^ and r2 are the inner  and  outer  radii
of the annular gap space in the analyzer,  L is the length  of
the collector rod between the aerosol entrance and the exit  slit,
and V is the applied voltage on the collector  rod.  Knowing  the
aerosol mobility from the above equation,  the  particle diameter,
Dp, can then be calculated as follows:
          DP ' T-TZ;

where e  is  the elementary unit of charge, C  is  the  slip  correc-
tion for  the particle, and y  is  the gas viscosity.   An accuracy
of  2% in  the calculated particle diameter can be  achieved  upon
carefully measuring  the flow  rates, the voltage,  and the dimen-
sions of  the mobility analyzer.

     In  addition  to  providing a  standard for particle size,  the
mobility  classifier  also provides a standard for  particle  con-
centration.  This  is based on the fact that  the particles  leaving
the analyzer are  predominantly singly charged.  By  sampling  these
particles into a  Faraday cup  and measuring the  corresponding
current  flow, I,  the particle concentration, N, can be calculated
as  follows:

          N =  (I  / e qe) K                                     (5)

where qe  is the aerosol flow  rate into the Faraday  cup  (the  elec-
trometer  current  sensor shown in Figure 3) and  K  is a factor
near unity  to correct for the presence of multiply  charged par-
ticles  in the output aerosol  stream.  Using  a high  sensitivity
electrometer  (Gary 401 vibrating reed electrometer, Varian In-
strument  Division, 611 Hansen Way, Palo Alto, CA  94303), currents
as  small  as 10~~16  A  can be measured.  Using  the standard aerosol
flow rate of qe =  22 £pm, particle concentrations as low as  2
particles/cm3 can  be determined.  The accuracy  in the measured
particle  concentration, after making a small correction  for  the
interference effect  of multiply  charged particles (see  the last
column  of Table 2  for the value  of the correction factor,  K) ,
is  about  5%.  Other  characteristics of the aerosol  generator'
are summarized in  Table 2.


                               268

-------
TABLE 2.   CHARACTERISTICS OF  THE MOBILITY CLASSIFIER GENERATOR FOR
                PRODUCING SUBMICRON  AEROSOL STANDARDS
                 (MODEL  3071 ELECTROSTATIC  CLASSIFIER,
            TSI,  INC.,  P.O. BOX 3394,  ST.  PAUL,  MN 55165)

Output
Diameter ,
ym
0.013
0.018
0.024
0.032
0.042
0.056
0.075
0.10
0.13
0.18
0.24
0.32
0.42
aerosol
Nominal
maximum
concentration,
cm~3
5,000
10,000
50,000
150,000
300,000
600,000
600,000
80,000
80,000
100,000
200,000
150,000
40,000
Input
Material
NaCl
NaCl
NaCl
NaCl
NaCl
NaCl
NaCl
OOP
OOP
OOP
OOP
OOP
OOP
aerosol
Solution
concentration,
% by wt
0.005
0.01
0.05
0.1
0.5
1.0
1.0
0.01
0.04
0.1
0.6
0.8
1.0
Operating conditions
mobility analyzer
Plow
rate,
qc £pmb
20
20
20
20
20
20
20
20
20
7
7
7
7
Collector Rod
Q
voltage , V
U of M
65
123
215
373
624
1064
1807
2994
466C
2750
4243
6381
9174
TSI
71
134
234
406
680
1159
1968
3260
5075
2995
4620
6949
9990
of
K
factord
1.0
0.99
0.98
0.96
0.93
0.90
0.86







The input aerosol  to the generator is obtained by atomizing an NaCl solution at
the indicated concentration with a Collison  atomizer operating at  241 kPa, or
in the case of the DOP aerosol, obtained by  the use of the vaporization-condensa-
tion technique described by Liu and Lee.21*   ag - 2 for the NaCl aerosol and
Cg - 1.2 for the DOP aerosol.

qc is the clean sheath air flow in the mobility analyzer.  Other flows are:
qa = qs - 0.1 qc,  where qa = flow rate of the polydisperse aerosol at input and
qs = flow rate of  the output monodisperse aerosol.

The collector rod  voltage given is based on  the following dimensions:

    U of M prototype:  r: = 0.950 cm, r2 = 1.907 cm, L = 45.52 cm
    TSI Model 3071:    r1 = 0.937 cm, r2 = 1.958 cm, L = 44.44 cm

    and assuming T = 21°C and P = 1 atmosphere.

K is a correction  factor to account for the  effect of doubly charged particles in
the calibration of condensation nuclei counters.  K is the ratio of the actual
particle concentration and the nominal concentration calculated by assuming all
particles are singly charged.
                                   269

-------
     In order to obtain a monodisparse  aerosol  with  the above
stated accuracies in particle size and  concentration,  several
conditions must be met:

     (1)   The number median diameter of  the  polydisperse aerosol
          at the classifier input should  be  kept  equal to or
          smaller than the desired diameter  of  the output mono-
          disperse aerosol.

     (2)   The 85Kr "neutralizer" should  have sufficient radio-
          activity and neutralizing volume to insure that the
          input aerosol is at Boltzmann  charge  equilibrium.

     (3)   For generating particles with  diameter  larger than
          0.08 ym, the a  of the input  aerosol  should  not exceed
          1.4.          g

      (4)  The flow must be laminar in  the mobility analyzer,
          and the flow ratio,  (q +qj/q^f should  be  kept small.
                                a.  S    G

      (5)  Conducting tubing should be  used to transport charged
          particles  in the monodisperse  output  aerosol stream
          and,  in addition, the charged  particles must be neu-
          tralized before being introduced into the  test instru-
          ments.

     Conditions  (1),  (2), and  (3) are  necessary in order to re-
 duce to  a minimum the  concentration of  the multiply  charged par-
 ticles of a  larger particle size that  have the  same  electrical
 mobility as  the primary  singly  charged  particles.

     Condition  (1) can be met by using  the proper solution concen-
 tration  in  the  atomizer  for generating  the input  polydisperse
 aerosols.  The  solution  concentrations  to be used with the Col-
 lison  atomizer  to obtain  the  indicated  number median diameters
 are shown in Table  2.   In no  case should  a more concentrated
 solution be  used, since  this  would lead to a higher  proportion
 of multiply  charged  particles  in the output  aerosol.

      In  the  case of  condition  (2), the  criteria described by
 Liu and  Pui22  can be followed  to design the  charge neutralizer
 to obtain Boltzmann  equilibrium on the  input polydisperse aerosol.

      In  the  case of  condition  (3), moderately monodisperse aero-
 sols,  such  as  those  produced  by the condensation  aerosol gen-
 erator can  be  used.21*

     Condition  (4)  is  necessary in order to  reduce  the range
 of mobility, and consequently  the range of particle  diameters
 passing  through  the  classifier.  To maintain laminar flow in
 the analyzer,  the critical  Reynolds number  should not be exceeded
 and the  flow rates  qa  and qc  must have the proper ratio.

                                270

-------
     Condition  (5) is necessary  in order  to  avoid  particle  pre-
cipitation due to charge build-up on  insulating  tubing.   Pre-
ferably, metal tubing should be  used  to transport  the  charged
particles.  If plastic tubing  is to be used,  the tubing  should
be rinsed with a detergent or  glycerine solution in  order to
form a conductive layer on the inside surface.

Generation of Ultrafine Monodisperse  Aerosols—

     An aerosol generator  is currently under development at the
Particle Technology  Laboratory for producing monodisperse aerosol
below 0.01 ym in particle  diameter.   '26   The generation method
is based on the rapid condensation of NaCl vapor in  a  cold  air
stream and the  controlled  coagulation of  the resulting ultrafine
aerosol.  The aerosol generator, shown schematically in  Figure
4, consists of  two major components:  the droplet  generation-
vaporization section and the aerosol  condensation-coagulation
section.

     To generate  an  aerosol with this system, an NaCl  solution
of known concentration  is  atomized with the  liquid atomizer to
form a polydisperse  spray.  The  spray is  then passed through
the diffusion dryer  to  evaporate the  water from  the  droplets.
The aerosol then  enters the evaporating tube in  which  the NaCl
particles are vaporized.   The  vapor  is then  injected into the
mixing nozzle,  where it encounters a  cold, primary dilution air
supplied to the nozzle  from a  filtered, dry  compressed air  source.
The rapid mixing  of  the vapor  and  the primary dilution air  causes
a fine NaCl aerosol  to  be  formed.  This aerosol  is then  allowed
to coagulate and  grow under controlled conditions.   It is sub-
sequently mixed with a  large volume of secondary dilution air
to "freeze" the particle size  distribution and to  transport the
aerosol to the  testing  instruments.   Particles as  small  as  0.003 vim
have been generated  with this  system.

Aerosol Generators of High Stability

     Several aerosol generators  of high stability  have been de-
veloped for use in a variety of  aerosol studies.  These  include
the constant output  atomizer21* for filtration, electrostatic
precipitation and other laboratory aerosol studies,  the  sulfuric
acid aerosol generator27 for studying the health effect  of  sul-
furic acid aerosol particles,  and  the constant-feed  fluidized-
bed dust generator28 for generating coal  dust and  other  solid
particles for use in instrument  calibration  and  other  studies.
Only the constant output atomizer  described  by Liu and Lee21t
will be further considered below.

     The constant output atomizer  is  shown schematically in
Figure 5.  The  generator makes use of a syringe  pump to provide
a constant flow of liquid  to a pneumatic  atomizer  to achieve
a stable aerosol  output.   In the conventional atomizer,  the


                               271

-------
        DIFFUSION!;
        DRIER
       COLLISOIM
       ATOMIZER
                          LINEAR
                          FLOWMETER
                          0-3 £pm     0-1 £pm TUBE
                                    FURNACE
   MIXING
'•7753 CHAMBER
            Kr-85
            NEUTRALIZER ^   ^ABSOLUTE
                   VALVETEXCESS FILTER
                          AIR
               DILUTION
               SYSTEM
                              °| ROTAMETER
                                0-30 gpm
                                          COMPRESSED
                                          AIR
                ABSOLUTE
                FILTER    DRIER  I  FILTER
                          PRESSURE
                          REGULATOR

               Figure 4. Schematic diagram of system for generating ultrafine
                       monodisperse aerosols.
       HEATING TAPE (192W AT 115V)

         ASBESTOS TAPE INSULATION

         PYREX GLASS TUBE (19 mm I.D.)
                ABSOLUTE
                FILTER
DRY
COMPRESSED
AIR      PRESSURE
         REGULATOR
    •j- ML i t
—CHS
                                            SCREEN (40 MESH)
                                                          115V

                                            VARIABLE TRANSFORMER
                                          EXCESS AEROSOL
                                              VALVE
                                             MIXING NOZZLE
                       SYRINGE PUMP
                                  EXCESS
                                  LIQUID
                                  RESERVOIR
                                     ROTAMETER
                                     0-100 Cpm
                                          VALVE
                                    DILUTION AIR
                  KRYPTON-85
                  CHARGE
                  NEUTRALIZER
                                                                AEROSOL OUT
              Figure 5. Schematic diagram of the constant output atomizer and
                      condensation aerosol generator.
                                        212

-------
solution being atomized is recirculated  and,  due  to  solvent
evaporation, the liquid in the atomizer  reservoir  becomes  more
concentrated with time, causing the output particle  size to
increase.  In the present device,  the  liquid  is not  recirculated.
The output particle size consequently  remains very stable.   The
device can also be used to generate monodisperse  aerosol of  high
stability.  With the addition of a heater and condenser, mono-
disperse DOP (di-octyl phthalate)  aerosols in the  0.03  to  1.3
pro diameter range can be generated.

Particle Size Accuracy of Monodisperse Aerosol Generators

     Among the several aerosol generation techniques discussed
above, three are capable of producing  particles with a  high
degree of accuracy in the generated particle  size.   The mono-
disperse aerosbls from the vibrating orifice  generator, the
mobility classifier generator, and latex suspensions all have
a stated accuracy in particle size of  better  than  2%.   Therefore,
it would be of interest to see whether such accuracy in size
can be realized in actual practice.

     Two types of comparisons have been  made  in our  Laboratory.
In one comparison, monodisperse aerosols of DOP were generated
by the vibrating orifice generator and their  size  determined
by the differential mobility analyzer  using an optical  particle
counter as the particle detector.  The size of the particles
was also calculated from the generator operating  conditions  using
equations  (1) and  (4).  This comparison  will  show  whether  the
vibrating orifice generator and the differential  mobility  analyzer
were operating with the stated accuracy.

     In a second comparison, monodisperse aerosols of polystyrene
latex  (PSL) were generated by aerosolizing the monodisperse  latex
suspensions using the usual spray-drying technique (see Whitby
and Liu14).  These latex suspensions were sized by their manu-
facturer  (Dow Diagnostics, P.O. Box 68511, Indianapolis, IN
46268) by electron microscopy.  By measuring  the  size of the
latex aerosols with the differential mobility analyzer, and  com-
paring it with the size supplied by the  manufacturer, one  can
obtain some ideas as to the reliability  of the particle size data
supplied by the manufacturer.

     The results of the comparisons are  shown in  Table  3.  We
found good agreement between the vibrating orifice and  the mo-
bility classification methods.  The maximum difference  between
the calculated particle diameters  based  on these  two methods
was 1.9%.  This difference is well within the combined  uncertain-
ties of these two independent methods.

     A larger discrepancy was found between the sizes of the
polystyrene latex particles supplied by  Dow Diagnostics and  that
determined by the differential mobility  analyzer,  the maximum

                               273

-------
NJ
     TABLE 3.  COMPARISON OF THE PARTICLE DIAMETER MEASURED BY THE  DIFFERENTIAL MOBILITY
         ANALYZER WITH DIAMETERS GIVEN BY THE MANUFACTURER  (PSL  PARTICLES)  AND THOSE
                GIVEN BY THE VIBRATING ORIFICE MONODISPERSE AEROSOL GENERATOR

Particle diameter, ym
Aerosol
DOP
DOP
DOP
PLS (LS-1010-E)
PSL(LS-061-A)
PSL(LS-1020-E)
PSL(LS-1029-E)
PSL(LS-1117-B)
PSL(LS-1166-B)
Generation method
Vibrating orifice
Vibrating orifice
Vibrating orifice
Spray-drying
Spray-drying
Spray-drying
Spray-drying
Spray-drying
Spray-drying
Given
by Dow Co.
—
—
—
0.357
0.365
0.481
0.500
0.79
1.10
Calculated
(vibrating orifice)
0.890
1.094
1.701
—
—
—
—
—
—
Measured
(differential mobility)
0.888
1.115
1.695
0.338
0.345
0.517
0.528
0.820
1.182
% Difference
+0.27
-1.9
+0.35
+5.6
+5.8
-6.9
-5.3
-3.7
-6.9

-------
difference being 6.9%.  A large part  of  the  discrepancy can
probably be attributed to the error in  the particle  size data
of the latex suspensions supplied by  the manufacturer.   Several
investigators have found similar discrepancies  in  the  particle
sizes supplied by Dow and the sizes determined  by  their indepen-
dent techniques.  Table 4 summarizes  these findings.   It is in-
teresting to note that most  techniques  give  particle sizes  which
deviate from the sizes given by Dow Chemical Co.  in  the same
direction (either larger or  smaller)  as  that given by  the mobility
classification method.  Further, the  average of the  sizes given
by these investigators agrees with the  size  determined  by the
mobility classification method to about  2%.

     Some of the frequently  mentioned causes for  the possible
sizing errors by electron microscopy  are:

      (1)  Due to the use of  emulsifier  in the latex  suspension,
          a thin layer of the emulsifier is  usually  present on
          the surface of the particles.   The thickness  of the
          emulsifier shell would vary with the  amount  of dilution
          used in preparing  the suspension.

      (2)  The particles, upon continuous electron  bombardment
          in the microscope, have been  found to change  in size-

     Nevertheless, a few percent error  in size  determination
for  the PSL particles is usually not  too serious  for most appli-
cations.  Consequently, the  nominal particle size  supplied  by
the  manufacturer can be used in these cases.  When more accurate
particle size data are needed, the actual particle size should
be determined by an appropriate technique capable  of giving the
required accuracy.

CALIBRATION OF AEROSOL MEASURING AND  SAMPLING INSTRUMENTS

     A variety of aerosol measuring and  sampling  devices have
been calibrated by means of  the monodisperse aerosol standards
described above.  These include the condensation  nuclei counter,
the  diffusion battery, the electrical aerosol analyzer, the opti-
cal  particle counter, and the inertial  impactor.   The  calibra-
tion studies have been reviewed in several papers  contained in
the  book, Fine Particles:  Aerosol Generation,  Measurement, Sam-1
pling, and Analysis, edited  by Liu.36  Therefore,  only  a few
of these calibration studies will be  reviewed here to  illustrate
the  application of the monodisperse aerosol  standards  and the
precautions in the use of the various aerosol generators for
instrument calibration and evaluation studies.

Condensation Nuclei Counter

     Several commercial condensation  nuclei  counters have been
calibrated by means of  the mobility  classifier  monodisperse aero-
sol  generator and the calibration  system shown  in Figure 3.

                               275

-------
          TABLE  4.   DIAMETERS OF  PSL PARTICLES GIVEN BY THE  MANUFACTURER  (DOW DIAGNOSTICS)
                              AND THOSE MEASURED BY DIFFERENT  INVESTIGATORS

PSL I.D.
LS1010-E
LS061-A
LS1020-E
LS1029-E
LS1117-B
LS1166-B

Dow
Co.
0.357
0.365
0.481
0.500
0.79
1.10

Mobility
classification
0.338
0.345
0.517
0.528
0.820
1.18

Average
of values
on right
0.334
0.340
- - -
0.516
_ _ _
- - -
Particle diameter, ym
Electron microscopy Light scattering Centrifuge Optical array
(1) (2) (3) (4) (5) (6) (7)
0.33 0.318 0.354
0.336 0.342 0.339 0.343
0.488
0.50 0.499 0.55



Investigators:
(1)  Heard et al.29
(3)  Davidson and Haller30
(5)  Dezelic and Kratohvil31
(2)  Porstenderfer  and Heyder
(4)  La Mer and Plesner3"*
(6)  Stbber and Flachsbart35
                                                                               33
               (7)  Davidson and Collins
                                       32

-------
In this  system,  the  particle concentration can be varied continu-
ously  by varying the ratio of aerosol and clean air flows.  A
critical orifice in  a vacuum line is used to draw a portion of
the  flow (3  fcpm)  through the electrometer.  The remaining aerosol
flow (20 Apm)  is then available for delivery to the nuclei coun-
ter  being calibrated.

      Due to  the  pulsating inlet flow common for most nuclei
counters, care must  be taken to insure that the flow rate of
the  calibrating  aerosol is larger than the peak suction flow
in the counter.   Further, in order to minimize precipitation
of particles in  the  sampling line and within the instrument due
to the charge on the particles, the test aerosol should be neutral-
ized before  being introduced into the counter.  The particle
loss inside  the  neutralizer should be evaluated and taken into
account  in the concentration calculation.

      Figure  6 shows  the calibration results for an Environment/
One  condensation nuclei counter.20  The response of the counter
is seen  to be linear at concentration levels only up to 130,000
particles/cm3, above which the response becomes non-linear.
Further, the indicated concentration of the counter is lower
than the true concentration by a factor ranging from 2.5 in the
lower linear range to 5.3 at the upper concentration limit,
600,000  particles/cm3, used in the calibration.

      Since all commercial nuclei counters have been referenced
by their manufacturer to the photoelectric counter of Pollak,37
the  above result suggests that the Pollak counter calibration
may  be in error.  However, in a subsequent study,38 a Pollak
counter  was  evaluated with the mobility classifier aerosol gen-
erator.   Figure  7 shows the results of the calibration study.
The  particle concentration determined by the Pollak counter using
the  original Pollak  calibration is seen to be in good agreement
with that determined by the mobility classification method, the
maximum  discrepancy  being 17% at the upper concentration limit
of 250,000 particles/cm3 used in the study.  The source of error
in the Environment/One counter calibration, therefore, must be
attributed to the calibration error made at the factory.

      The response of the condensation nuclei counters has also
been evaluated as a  function of particle size.  The result for
/the  case of  the  General Electric counter is shown in Figure 8.25
The  counting efficiency  (ratio of indicated concentration to
input aerosol concentration) of the GE counter is found to drop
rapidly  below 0.02 um, reaching a value of 50% at a particle
diameter of  90 A.

      Similar studies on the counting efficiency of the GE and
Environment/One  counters by Cooper and Langer39 have resulted
in a similar finding.  The study by Bricard et al.*0 on the con-
tinuous  flow counter using alcohol as the working fluid also

                                277

-------
            CMC NO. 1 (ENVIRONMENT/ONE, SERIAL NO. 149)

                                         0
             50   100  150   200  250   300  350   400  450   500  550

                 ACTUAL NUCLEI CONCENTRATION, 103 (PARTICLES/cm3)
600
          Figure 6. Response of the Environment/One, Rich WO condensation
                nuclei counter to monodisperse aerosols produced by the
                mobility classifier aerosol generator.

gives similar results.   Recently, Porstendorfer  and Soderholm
have also found  the size dependence of the Environment/One  count-
er using  a photographic counting-diffusion battery technique. **l
The cause of  this  non-ideal behavior has  not  yet been identified
at the present time,  but it seems that this non-ideal behavior
is an inherent characteristic of most of  the  automatic condensa-
tion nuclei counters.

Diffusion Battery

     The  mobility  classifier aerosol generator has also been
used for  calibrating  the diffusion batteries  described by Sin-
clair et  al."2'1*3   In the first calibration study, the diffusion'
battery comprised  of  the "collimated holes structures" was  used.
These are metal  discs with uniform size  holes.  Since the number,
the diameter, and  the length of these uniform tubular holes can
be measured accurately with a microscope,  the penetration of
a monodisperse aerosol of a known particle size through the bat-
tery can  be predicted from the diffusion  theory.  In the cali-
bration study, monodisperse aerosols of  various diameters were
generated by  the mobility classifier generator, and the particle
penetration through the battery was measured  with a condensation
                                278

-------
co
UJ
o  100
t
a.
Z
o
a.
    10
z
UJ
O
O
o
8
oc
UJ
   0.1
  I  I  I  I I I I
                                I    I
                                          I I I I
       -o
O  0.05 urn NaCI
•  0.088 jum NaCI
A  0.032 jum NaCI
A  0.025 /L/m NICHROME
O  0.032 Aim NICHROME
•  0.11 ,um NaCI
O  0.15 jum NaCI
                                            IDEAL
                                            RELATIONSHIP
                                   ACTUAL
                                   CALIBRATION
                                   Np = 0.971xN£
0.972
                                                   I    I  I  I  I 111
     0.1                   1                   10                 100
             AEROSOL CONCENTRATION(ELECTRICAL), NE, 103 PARTICLES/cm3

            Figure 7. Calibration of the Pollak counter with the mobility
                     classifier aerosol generator.
                                     279

-------
   1.0

   0.9

   0.8
z
2  0.7

cc  0.6
Z
   0.5

   0.4

   0.3

   0.2

   0.1
       0.0
                            GECNC
                            CAT 112L428G1
                            NO 3264181
                            O SINGLY CHARGED PARTICLES

                            A NEUTRALIZED PARTICLES
0.00   0.01    0.02   0.03   0.04   0.05   0.06

                    PARTICLE DIAMETER, jum
                                                   0.07
                                                    0.08
0.09
          Figure 8. Counting efficiency of the General Electric condensation
                 nuclei counter as a function of particle size.

nuclei counter.   Figure 9 compares the  particle penetration
determined experimentally with that predicted from theory.  The
agreement is  seen to be very good  in the  tested size range from
0.024 ym to 0.110 urn.   The good agreement  constitutes a direct
verification  of  the theory of diffusion battery.

Electrical Aerosol Analyzer
     The electrical aerosol analyzer is an aerosol size distribu-
tion measuring device  operating on the  principle of unipolar
diffusion charging and mobility analysis. •* **   The analyzer operates
by first placing a unipolar charge on the  aerosol being measured,
and measuring the resulting mobility distribution of the charged
particles by  means of  a mobility analyzer.  Although the charge
acquired by an aerosol particle under a specific set of charging
conditions can be calculated theoretically using the available
charging theories,^5 the uncertainties  in  the theoretical results,
particularly  that caused by the particle  loss in the instrument,
require that  the instrument be calibrated.  In the calibration
study reported by Liu and Pui,41* the mobility classifier gen-
erator was used  to generate monodisperse  aerosols of a known
size and concentration for the study.

     Some sample results from the  calibration are shown  in  Fig-
ure 10.  The  figure shows the empirical voltage-current  for  the
electrical aerosol analyzer upon exposure to monodisperse  aerosols
                                280

-------
                              BATTERY NUMBER
                              9         10
O
UJ
Q.
                                                        Aim DIAMETER
                                                        Aim DIAMETER
                                                        Aim DIAMETER
                                                     0375 Aim DIAMETER
                                                        Aim DIAMETER
                         2345
                            EQUIVALENT LENGTH, km
       Figure 9. Comparison of theoretical (solid lines) and experimental
                penetrations through the Sinclair diffusion battery using
                monodisperse aerosols from the mobility classifier generator.
                                   281

-------
    D
    §
    X
    LL
    O
    1-
    z
    111
    DC
    OC

    U
    OC
    UJ
    O
    OC

    U
                                           SMOG   I* Dp = 0.0105 urn
         Dp = 0.0125

              0.018
              0.024
              0.032
              0.042
              0.056
              0.075
                                                             70V
                         1000
10000
                                                           100000
                          COLLECTOR ROD VOLTAGE, V

          Figure 10.  Response of electrical aerosol analyzer to monodisperse
                  aerosols.

of various sizes.   These  curves can be used to construct a cali-
bration matrix which  can  be used in a data  reduction algorithm1*6
for the inversion of  instrument data to obtain the  original size
distribution.

Optical Particle Counter

     Several  commercial optical particle counters  have been eval-
uated by means of the latex aerosols and aerosols  produced by
the vibrating orifice generator.1*7  Since the  response of the
optical counter  is  a  function of the size,  the refractive index,
and the shape of the  measured particle, a variety  of test aero-
sols is needed in order to determine the instrument response
empirically.   The ability of the vibrating  orifice generator
to generate aerosol from  a variety of materials  has made this
an ideal generator  for studying the response of  optical counters.
Materials with a variety  of refractive indices,  such as the
Cargille  index-of-refraction liquids, methylene  blue, sodium
chloride and  India  ink, may be dissolved or diluted in a suitable
solvent and used in the generator to produce aerosols with the
desired optical  properties.
                                282

-------
     Some typical results for the Royco  220  particle  counter
are shown in Figure 11.  The response of  the counter  is  shown
as a function of particle size and particle  refractive  index.
Such information can be used for determining the  effect  of  the
refractive index on the measurement accuracy of the instrument.

     Calibrations of the optical particle  counters using irregular
particles have also been performed.  In  one  study, coal  dust
particles obtained by aerosolizing a finely  ground coal  powder
with the fluidized bed were used. 8  The  polydisperse coal  aero-
sol generated by the fluidized bed aerosol generator  was passed
through a differential mobility analyzer  to  extract a monodis-
perse fraction, and the resulting monodisperse aerosol was  then
applied to the optical counter for calibration.   In another
study, inertial impactors of various cut  sizes were placed  at
the inlet of the optical counter and the  response of  the optical
counter was determined, from which an "aerodynamic" calibration
could be obtained.1*9

Inertial Impactor

     The inertial  impactor  has  found widespread use  in  aerosol
studies because of  its  simplicity and well defined operational
characteristics.  Various designs of  impactors are available
commercially for different  applications.50'51 An extensive theo-
retical analysis of the inertial  impactor has been performed
by Marple52 and Marple  and  Liu.53'5%  Although the impaction
efficiency can now  be  accurately predicted by theory, experi-
mental evaluation  still must be made  in  order to  characterize
the real impactor  behavior,  including problems due to particle
reentrainment and  bounce.

     Many impactors have been calibrated by  means of  the vibrat-
ing orifice monodisperse aerosol generator.   Two  different  ap-
proaches can be used  in the calibration.   In one  approach,  an
optical counter is  used as  a particle detector.   By  counting
the particles upstream  and  downstream of the impactor,  the  col-
lection efficiency  can  be obtained.   In  another approach,the
particles are tagged  with a fluorescent  tracer, and  the particles
deposited on various  stages of  the  impactor, including  the  after
filter, are measured  fluorometrically,  from  which the impaction
characteristics are determined.  This latter technique  is especi-
ally useful for evaluating  the multistage impactors,  since  the
wall losses can also  be evaluated.

     Figure 12 shows  the calibration  results for  a  single-stage
impactor and a two-stage impactor consisting of  two  identical
impaction nozzles.1*9   The experimental  results  are  seen to  agree
well with the theoretical prediction.   The monodisperse aerosols
from the vibrating  orifice  generator  have also  been  used to eval-
uate the Lundgren  impactor,  the Andersen impactor,  and  the  Sierra
impactor55"57 as well  as the virtual  impactor.51   Using the latex


                               283

-------
                 10
              o
              QC
              W

              Z
              D
              O
              O
                 .1
                   _ j I 11II     I    I  I  I


                       REFRACTIVE INDEX, m

                       O  1.6
                       •  1.6 (PSD
                       A  1.4
                 6 ~
    EXPERIMENTAL
    m = 1.49
                     I I ml
                                  ROYCO PC 220
I   I   1  I I  Mil
                          1                  10
                           PARTICLE DIAMETER, jum

        Figure 11. Experimental calibration curve for the Royco 220 optical
                particle counter.

aerosols, Rao  and  Whitby have also studied  the particle bounce
phenomena inside  impactors.5tf>59

Comparative Studies  Between  Aerosol Measuring Instruments

     In the preceding  sections, we have discussed the calibration
of various aerosol measuring instruments with monodisperse aero-
sol standards.   If the instruments are properly calibrated and
the data properly  analyzed,  different instruments should give
the same measurement results when they are  used on the same
aerosol.  Such comparative studies involving  the simultaneous
aerosol measurement  of the same aerosol by  different measuring
instruments are the  subjects of this section.

     The electrical  aerosol  analyzer (EAA)  is capable of measur-
ing particle size  distribution in the 0.005 to 1.0 urn diameter
                                284

-------
    HI
    u
    2
    HI
    u
    LL
       1.0
       0.9
       0.8
       0.7
       0.6
0.5
       0.4
       0.3
       0.2
       0.1
—I	1	1	T
    S/W = 1.4
    Re = 850
    T/W = 7


    THEORETICAL

 A - SINGLE
 B - DOUBLE
    UNIFORM PARTICLE
    DISTRIBUTION
    ACROSS ENTRANCE
 C- DOUBLE
    PARTICLES IN CENTRAL!
    80% OF FLOW
    AT ENTRANCE
        EXPERIMENTAL

    O SjumVOMAG ORIFICE
    D 10 pm VOMAG ORIFICE
              I
            I
                  I
             I	I
             0.1
           0.2
            0.3   0.4
0.5
0.6
0.7
0.4   0.5   0.6   0.7
           Figure 12.  Comparison of theoretical and experimental efficiency
                    curves for two impactors.

range.   The measured  distribution can  be  integrated to yield
the number and volume concentrations.  Therefore, the EAA may
be compared with a condensation nuclei counter (CNC) and a gravi-
metric  analysis technique  for  number and  volume concentration
determinations.  Such comparisons have been  made, the detail
of which will be described in  a forthcoming  paper by Mulholland
et al.60  Some preliminary results of  this  study are described
below.

     For number concentration  determinations,  polydisperse aero-
sols of  NaCl,(NH^)2SO^,  DOP, and sucrose  were  generated by the
constant output atomizer and supplied  to  two EAA's and a GE CNC.
In Figure 13, the  total  number concentrations  measured by.the
EAA's are compared with  that measured  by  the CNC.  It is seen
that good agreement is obtained between the  two different measur-
ing techniques.  It should be  mentioned that the CNC had been
calibrated several months  prior to the experiment, and that the
                                 285

-------
                                IDEAL RELATIONSHIP
13                10              30

       AEROSOL CONCENTRATION (CNC), NC, 103 PARTICLES/cm3

Figure 13.   Comparison of BAA and CNC for total number concentration
           measurements obtained in the first experimental series.
100
                            286

-------
EAA concentrations were  calculated  by the simplified data  reduc-
tion  procedure  of Liu and Pui"*1* using the instrument sensitivi-
ties  for monodisperse aerosols.

      In the second series of experiments, the  CNC was recali-
brated, and a  simplex minimization  program of  Liu and Kapadia61
was used for reducing the EAA data.   The results of the  compar-
ison  are shown  in Figure 14.  Very  good agreement is obtained,
the maximum discrepancy  being about 10%.
     CO

      I
      111
     m
      o

       o
      Z

      O
      Z
      o
        100
50
      111
      o
      o
      u
      _l
      o
      CO
      o
      cc
10
                           I   I  I  I  I
DATA REDUCTION TECHNIQUE

O POLYDISPERSE SENSITIVITY (LIU & KAPADIA, 1977)

• MONODISPERSE,SENSITIVITY (LIU & PUI, 1975)
                                          IDEAL RELATIONSHIP
                              5        10                 50

                AEROSOL CONCENTRATION (EAA), NE, 103 PARTICLES/cm3
                                                       100
         Figure 14.  Comparison of EAA and CNC for total number concentration
                  measurements obtained in the second experimental series.
                                  287

-------
SUMMARY AND CONCLUSIONS

     In this paper, we have reviewed the recent  developments in
monodisperse aerosol generation.  Some of the  techniques  developed,
such as the vibrating orifice generator and  the  mobility  classi-
fier generator, are capable of generating monodisperse  aerosols
of an accurately known particle size and concentration.   These
aerosols can be referred to as "aerosol standards"  since  they
can be used as standards of measurement or calibration  in the
field of aerosol science.  The application of  these monodisperse
aerosol standards to instrument calibration  and  evaluation has
also been briefly described and some sample  results presented.
It is shown that with proper calibration of  the  instruments used,
aerosol measurement can be made with good accuracy  as in  many
other fields of science and technology.

REFERENCES

 1.  La Mer, V.K., and D. Sinclair.  An Improved Homogeneous  Aero-
     sol Generator.  OSRD Report No. 1668, Office of Publication
     Board, U.S. Department of Commerce, Washington, DC,  1943.

 2.  Rapaport, E., and S.G-  Weinstock.   A Generator  for Homo-
     geneous Aerosols.  Experientia 11:363-364, 1955.

 3.  Liu, B.Y.H.,  K.T. Whitby,  and H.H.S.  Yu.  A Condensation
     Aerosol Generator for Producing Monodispersed Aerosols in
     the Size Range 0.036 urn to 1.3 ym.  J.  Rech. Atmos.  3:397-
     406, 1966.

 4.  Kogan, I., and S. Burnasheva.  Zh. Fiz. Khim.  34:2630, 1960.

 5.  Fuchs, N.A.,  and A.G. Sutugin.  Generation and Use of Mono-
     disperse Aerosols.  In:   Aerosol Science, C.N. Davies, ed.
     Academic Press, New York,  1966.  pp.  1-30.

 6.  Espenscheid,  W., E. Matijevic, and M.  Kerker.  J. Phys.
     Chem. 68:2831, 1964.

 7.  Walton, W.H., and W.C.  Prewett.  The Production of Sprays
     and Mists of Uniform Drop Size by Means of Spinning  Disc
     Type Sprayers.  Proc. Phys.  Soc. (London) 62:341-350,  1949.

 8.  May, K.R.  An Improved Spinning Top Homogeneous Spray  Ap-
     paratus.  J.  Appl. Phys. 20:932-938,  1949.

 9.  Boshoff, W.  Proc. Inst. Mech. Engrs.  166:443,  1952.

10.  Schwendiman,  L.C., A. K. Postma, and L.F. Coleman.   A Spin-
     ning Disc Aerosol Generator.  Health Phys.  10:947-953,  1964.
                               288

-------
11.   Whitby, K.T., D.A. Lundgren,  and C.M.  Peterson.   Homogeneous
     Aerosol Generators.  Int. J.  Air Water  Pollut.  9:263-277,
     1965.

12.   Lippmann, M., and R.E. Albert.  A  Compact  Electric-Motor
     Driven Spinning Disc Aerosol  Generator.  J.  Am.  Ind.  Hyg.
     Assoc. 28:501-506, 1967.

13.   Philipson, K.  On the Production of  Mon©disperse Particles
     with a Spinning Disc.  J. Aerosol  Sci.  4:51-57,  1973.

14.   Whitby, K.T., and B.Y.H. Liu.   Polystyrene Aerosols—Elec-
     trical Charge and Residue Size  Distribution.  Atmos.  Environ.
     2:103-116, 1968.

15.   Langer, G-,  and A. Lieberman.   Anomalous Behavior  of  Aerosols
     Produced by  Atomization of  Monodisperse Polystyrene Latex.
     J. Colloid Sci. 15:357-360,  1960.

16.  Fuchs, N.A., and A.G. Sutugin.  Kolloid. Zh.  25:487,  1963.

17.  Raabe, O.G.  The Generation of  Aerosols of Fine  Particles.
     In:   Fine Particles:  Aerosol Generation,  Measurement,
     Sampling and Analysis, B.Y.H.  Liu, ed.  Academic  Press,  New
     York,  1976.  pp.  57-110.

18.  Berglund, R.N., and  B.Y.H.  Liu. Generation  of Monodisperse
     Aerosol  Standards.   Environ.  Sci.  Technol. 7:147-153,  1973.

19.  Liu,  B.Y.H.  Standardization and Calibration of  Aerosol
     Instruments.   In:  Fine Particles:  Aerosol  Generation,
     Measurement, Sampling and Analysis,  B.Y.H. Liu,  ed.   Aca-
     demic  Press, New York, 1976.  pp.  39-53.

20.  Liu,  B.Y.H., and D.Y.H. Pui.  A Submicron  Aerosol Standard
     and  the  Primary, Absolute Calibration  of the Condensation
     Nuclei Counter.  J.  Colloid Interface  Sci. 47:155-171,  1974.

21.  Liu,  B.Y.H., and D.Y.H. Pui.  Equilibrium  Bipolar Charge
     Distribution of Aerosols.   J. Colloid  Interface  Sci.  49:305-
     312,  1974.

22.  Liu,  B.Y.H., and D.Y.H. Pui.  Electrical Neutralization
     of Aerosols.  J. Aerosol  Sci.  5:465-472, 1974.

23.  Knutson, E.O., and K.T. Whitby. Aerosol Classification
     by Electric  Mobility:  Apparatus,  Theory and Applications.
     J. Aerosol Sci. 6:443-451,  1975.

24.  Liu,  B.Y.H., and K.W. Lee.   An  Aerosol Generator of  High
     Stability.   J. Am. Ind. Hyg.  Assoc.  36:861-865,  1975.
                               289

-------
25.   Liu, B.Y.H., and C.S. Kim.  On the Counting Efficiency  of
     Condensation Nuclei Counters.  Atmos. Environ.  11:1097-1100,
     1977.

26.   Kim, C.S.  Ultrafine Aerosol Studies:  Generation,  Measure-
     ment and Coagulation.  Ph.D. Thesis, Mechanical Engineering
     Department, University of Minnesota, Minneapolis, MN,  1978.

27.   Liu, B.Y.H., and J. Levi.  Generation of Sulfuric Acid  Aero-
     sols for Health Effects Studies.  Report to the U.S.  Environ-
     mental Protection Agency, Publication No.  341,  Particle
     Technology Laboratory, Mechanical Engineering Department,
     University of Minnesota, Minneapolis, MN,  1978.

28.   Marple, V.A., B.Y.H. Liu, and K.L. Rubow.  A Dust Generator
     for  Laboratory Use.  J. Am. Ind. Hyg. Assoc. 39:26-32,  1978.

29.   Heard, M.J., A.C. Wells, and R.D. Wiffen.  A Re-Determina-
     tion of the Diameters of Dow Polystyrene Latex  Spheres.
     Atmos. Environ. 4:149-156, 1970.

30.   Davidson, J.A., and H.S. Haller .   Latex Particle Size Analy-
     sis.  Part V — Analysis of Errors in Electron Microscopy.
     J. Colloid Interface Sci. 47:459-472, 1974.

31.   Dezelic, G., and J.P. Kratohvil.   Determination of Particle
     Size of Polystyrene Latexes by Light Scattering.  J. Colloid
     Sci. 16:561, 1961.

32.   Davidson, J.A., and E.A. Collins.  Particle Size Analysis.
     Part IV — Comparative Methods for Polyvinyl Chloride Latex.
     J. Colloid Interface Sci. 40:437-447, 1972.

33.   Porstendorfer , J., and J. Heyder.  Size Distribution of
     Latex Particles.  J. Aerosol Sci. 3:141-148, 1972.

34.   La Mer, V.K., and I.V. Plesner.  J. Polymer Sci  24:147,
     1957.

35.   Stober, W. , and H. Flachsbart.  High Resolution Aerodynamic
     Size Spectrometry of Quasi-Monodisperse Latex Spheres with
     a Spiral Centrifuge.  J. Aerosol Sci. 2:103-116, 1971.

36.   Liu, B.Y.H., ed.  Fine Particles:  Aerosol Generation, Mea-
     surement, Sampling and Analysis,  Academic Press, New York,
     1976 .

37.   Pollak, L.W., and A.L. Metnieks.   Intrinsic Calibration
     of the Photoelectric Nucleus Counter Model 1957, with Con-
     vergent Light Beam.  Tech. Note 9, Contract
                               290

-------
38.  Liu, B.Y.H., D.Y.H. Pui, A.W. Hogan,  and  T.A.  Rich.   Cali-
     bration of the Pollak Counter with Monodisperse  Aerosols.
     J. Appl. Meteorol. 14:46-51, 1975.

39.  Cooper, G., and G. Langer.  Limitations of  Commercial Con-
     densation Nucleus Counters as Absolute Aerosol Counters.
     J. Aerosol Sci. 9(2):65-75, 1978.

40.  Bricard, J., G. Madelaine, and M.-L.  Perrin.  Comparison
     of the Size Distribution of a Submicronic Aerosol Obtained
     by the Diffusion Battery Method  and Electrical Aerosol
     Analyzer.  Presented at the Ninth International  Conference
     on Atmospheric Aerosols, Condensation and Ice Nuclei, Gal-
     way, Ireland, Sept. 21-27, 1977.

41.  Porstendorfer, J., and S.S. Soderholm.  Particle Size Depen-
     dence of a Condensation Nuclei Counter.   Atmos.  Environ.,
     in press.
42.  Sinclair, D., R.J. Countess, B.Y.H. Liu,  and D.Y.H. Pui.
     Experimental Verification of Diffusion Battery Theory.
     J. Air Pollut. Contr. Assoc. 26:661-663,  1976.

43.  Sinclair, D., R.J. Countess, B.Y.H. Liu,  and D.Y.H. Pui.
     Automatic Analysis of Submicron  Aerosols.   Presented at
     the Aerosol Measurement Workshop, University of  Florida,
     Gainsville, FL, March, 1976.

44.  Liu, B.Y.H., and D.Y.H. Pui.  On the  Performance of the
     Electrical Aerosol Analyzer.  J. Aerosol  Sci. 6:249-264,
     1975.

45.  Liu, B.Y.H., and D.Y.H. Pui.  On Unipolar Diffusion Charging
     of Aerosols in the Continuum Regime.  J.  Colloid Interface
     Sci. 58:142-149, 1977.

46.  Liu, B.Y.H., D.Y.H. Pui, and A.  Kapadia.  Electrical Aerosol
     Analyzer:  History, Principle and Data Reduction.  Presented
     at Aerosol Measurement Workshop, University of Florida,
     Gainsville, FL, March, 1976.

47.  Liu, B.Y.H., R.N. Berglund, and  J.K.  Agarwal.  Experimental
     Studies of Optical Particle Counters.  Atmos. Environ.
     8:717-732, 1974.

48.  Liu, B.Y.H., V.A. Marple, K.T. Whitby, and  N.J.  Barsic.
     Size Distribution Measurement of Airborne Coal Dust by
     Optical Particle Counters.  J. Am. Ind. Hyg. Assoc. 35:443-
     451, 1974.

49.  Marple, V.A., and K.L. Rubow.  Aerodynamic  Particle Size
     Calibration of Optical Particle  Counters.   J. Aerosol Sci.
     7:425-433, 1976.

                               291

-------
50.  Marple, V.A., and K. Willeke.  Inertial Impactors:   Theory,
     Design and Use.  In:  Fine Particles:  Aerosol Generation,
     Measurement, Sampling and Analysis, B.Y.H. Liu, ed.   Aca-
     demic Press, New York, 1976.  pp. 411-446.

51.  Loo, B.W., J.M. Jaklevic, and F.S. Goulding.  Dichotomous
     Virtual Impactors for Large-Scale Monitoring of Airborne
     Particulate Matter.  In:  Fine Particles:  Aerosol  Genera-
     tion, Measurement, Sampling and Analysis, B.Y.H.  Liu,  ed.
     Academic Press, New York, 1976.  pp. 311-350.

52.  Marple, V.A.  A Fundamental Study of Inertial Impactors.
     Ph.D. Thesis, Mechanical Engineering Department,  University
     of Minnesota, Minneapolis, MN, 1970.

53.  Marple, V.A., and B.Y.H. Liu.  Characteristics of Laminar
     Jet Impactors.  Environ. Sci. Technol. 8:648-654, 1974.

54.  Marple, V.A., and B.Y.H. Liu.  On Fluid Flow and  Aerosol
     Impaction in Inertial Impactors.  J. Colloid Interface Sci.
     53:31-34, 1975.

55.  Rao, A.K., and K.T. Whitby.  Non-Ideal Collection Character-
     istics of Single-stage and Cascade Impactors.  J. Am.  Ind.
     Hyg. Assoc.  38:174-179, 1977.

56.  Willeke, K.  Performance of the Slotted Impactor.   J. Am.
     Ind. Hyg. Assoc. 36:683-691, 1975.

57.  Willeke, K., and J.J. McFeters.  The Influence of Flow Entry
     and Collecting Surface on the Impaction Efficiency  of  Inertial
     Impactors.   J. Colloid Interface Sci. 53:121-127, 1975.

58.  Rao, A.K., and K.T. Whitby.  Non-Ideal Collection Character-
     istics of Inertial  Impactors—I.  Single-stage Impactors
     and Solid Particles.  J. Aerosol Sci. 9:77-86, 1978.

59.  Rao, A.K., and K.T. Whitby.  Non-Ideal Collection Character-
     istics of Inertial  Impactors—II.  Cascade Impactors.  J.
     Aerosol Sci. 9:87-100, 1978.

60.  Mulholland,  G.W-, B.Y.H. Liu, A. Kapadia, and D.Y.H.  Pui.
     Aerosol Number and Mass Concentration Measurements-   A Com-
     parison of the EAA with Other Measurement Techniques,  to
     be  submitted for publication.

61.  Liu, B.Y.H.  and A. Kapadia.  A Computer Data Reduction Pro-
     gram for the Electrical Aerosol Analyzer.  Publication No
     325, Particle Technology Laboratory/Mechanical Engineering
     Department,  University of Minnesota, Minneapolis, MN? ?977
                               292

-------
                              PAPER 13
             SUBSTRATE COLLECTORS FOR CASCADE IMPACTORS
                           AN EVALUATION

                          D. BRUCE HARRIS
                    PROCESS MEASUREMENTS BRANCH
          INDUSTRIAL ENVIRONMENTAL RESEARCH LABORATORY-RTP
                U.S.  ENVIRONMENTAL PROTECTION AGENCY

                                AND

                       G.  CLINARD, L.G.  FELIX
                       G. LACEY,  J.D. MCCAIN
                    SOUTHERN RESEARCH INSTITUTE

     The  use of cascade  impactors to obtain particle  size  in-
formation on process  streams has  increased dramatically  in  the
past few years.  The  Process Measurements  Branch  (PMB) of  EPA's  In-
dustrial  Environmental Research  Laboratory-RTP has  been  involved
in investigating their performance  and  application  for almost
a decade.  Early in  this  effort  we  recognized the  inherent  po-
tential for  error caused  by the  small sample  weights  on  the heavy
metal collection stages  being  used  in commercially  available
impactors, and  proposed  and implemented the use of  light weight
substrates.  Many problems were  met  and resolved during  the evo-
lutionary development of  the methodologies of using cascade
impactors.

     Substrates have  generally been  made of filter  media (most
often fiber  glass)  and thin metal foils.   An  early  study of sub-
strate usage was included in a test  of  a then-available  commercial
impactor at  a coal-fired  power plant in 1973  and has  been  re-
ported in detail in  EPA  report "Field Measurements  of Particle
Size Distribution with Inertial  Sizing  Devices," EPA-650/2-73-
035  (NTIS No. PB 226292).  The advantages  of  substrates  were
demonstrated and the  method became  the  one recommended for  IERL-
RTP use.

     Weight  loss problems were reported by some users of fiber
glass substrates.  A  detailed  study  of  this problem was  made
by Southern Research  Institute under contract to EPA's PMB.
It found that most of the trouble was due  to  careless handling
and suggested procedures  to be used  to  limit  the errors  to  a
reasonable level.  The detailed  report  is  available:   "Andersen
Filter Substrate Weight Loss," EPA-650/2-75-022  (NTIS No.  PB
240720).

                               293

-------
     Many investigators  opted not to use filter  media:  instead,
thin metal foils,  usually  aluminum or stainless  steel,  were used
to solve the weight  loss problem previously noted  with  fiber
glass.  Many found that  these solid metal  surfaces had  a problem
which had been  observed  with the original  collection surfaces
supplied by the manufacturer — particles tended  to bounce off
the collection  surface.  An obvious solution  was to increase
the stickiness  of  the  surface, usually by  coating  it with grease.
This appeared to solve much of the problem; however, a  grease
that worked at  one source  might not work at another test.

     In the meantime,  people were reporting anomalous weight
gains with the  fiber glass substrates, including variations with
temperature  (Figure  1) and between various fiber glass  filter
types  (Figure 2).   As  the  depth of this problem  became  evident,
EPA's PMB again asked  SoRI to investigate  the whole problem of
substrate use in cascade impactors.  A detailed  laboratory study
was conducted,  utilizing many fiber glass  filter media  and metal
foil greases.
            - COAL FIRED POWER BOILERS
          0  PORTLAND CEMENT KILN
    100
                              200           250

                            GAS TEMPERATURE. °C
300
          Figure 1. Anomalous mass increases of Andersen glass fiber impact/on
                substrates at different flue gas temperatures.
                                294

-------
    1.5
    1.0
Ol
o
V)
V)
    0.5
      100
               • GELMAN TYPE A (OLD)
               O GELMAN SPECTRO GRADE TYPE A
               £ MSA 1106 BH
               0 REEVE ANGEL 900 AF
                                     CEMENT
                                     PLANT
                                     50 PPM
                                     SO2
                    COAL FIRED POWER BOILER   X
                    550 PPM SO2             X ^
                                                 X

                                                      X
                                                        X
                                                          X
200               300

       TEMPERATURE, °C
                                                             400
 Figure 2. Anomalous mass gains of various 47 mm diameter glass fiber filters
         at different temperatures (60 minute samples at flow rates of 0.25 acfm).
                                   295

-------
     Many investigators had reported extraneous mass gains  on
ambient filter media due to S02/S03 conversion on  the  filter
to sulfates.  The laboratory screening tests were  run  to  under-
stand what occurs during this mass gain and to select  a material
sufficiently inert for use as instack impactor substrates.  A
suitable material would be one which has stable low mass  charac-
teristics and is mechanically strong enough to resist  cutting,
tearing, and loss of material.  Two laboratory test methods were
used:  one employed a flow of gaseous S02 through  the  filter
media  (Figure 3); the other involved soaking the material in
hot sulfuric acid solution.  The results of the gas flow  studies
are summarized in Table 1, which includes two materials which
had been soaked in sulfuric acid.  One fiber glass material
(Reeves Angel 934AH) stands out for use as substrate media.
Since manufacturers sometimes change processes without changing
the media name, the substrates should be checked when  received
for conformity with previous batches.  A pH stability  test, for
long term levels around 7, can be a good indicator.

     Control of particle bounce and deposit scouring from metal
foil substrates has been demonstrated for a number of grease
coatings.  The principal difficulty noted has been the deleterious
effect of elevated temperature on their physical and chemical
characteristics.  Changes in viscosity sufficient  to remove the
grease from the collection surface and chemical breakdown to
hard brittle masses have been noted.

     A laboratory screening test was used, consisting of  heating
each grease in an oven for several hours, followed by examination
of the material for changes in consistency, color, and mass.
Of the many materials tested, Dow Corning silicone and Apiezon
greases were the only ones to exhibit sufficient stability  to
warrant field testing.


     The field test was conducted at a coal-fired power plant.
Each impactor was loaded with the greased stages and the  normal
backup filter.  A Gelman 47 mm prefilter was attached to  the
inlet to ensure that only gas (no particulate)  would flow through
the impactor, which was horizontal in the stack.

     The two Dow Corning greases (Molycote III and Silicone High
Vacuum) lost measurable weight from the stages and added  weight
to the backup filter.  It was decided that these did not  have
the stability needed for instack use.  The Apiezon tests  are
summarized in Table 2.  The only grease not to lose weight  was
Apiezon H, which actually gained.  Close examination of the
stages revealed a fine even layer of dust, probably deposited
during loading and unloading of the unit.  Jet patterns were
barely visible on most stages and a uniform coating of grease
remained.  No evidence of overflow was noted.  An  extended  test
                               296

-------
w
to
vo
-J
               SO2
                           AIR
                                                     PREHEAT

                                                     COILS
                                                                          1
                                             SAMPLE CONDITIONING

                                             CHAMBER
                                                 OVEN
                                                                                           HUMIDIFIER
                                                                                          1
                                                                                      AIR-SO2 EXHAUST
                                                                                                              HEATER TAPE
   WATER HEATER








AIR FLOW DIRECTION



SO2 FLOW DIRECTION



AIR-SO2 MIXTURE

   FLOW DIRECTION
                                          Figure 3. Diagram of experimental set-up for filter substrate

                                                   conditioning experiment.

-------
               TABLE  L.   MASS GAINS  OF 47 mm  GLASS FIBER  FILTER SUBSTRATE MATERIALS
                                    FROM LABORATORY CONDITIONING3
	
b
Material
Reeve Angel
934AH
Gelman AE
Gelman Spectro
Glass
Whatman
GF/A
Reeve Angel
934AH
Gelman AE
Gelman Spectro
Glass
Whatman GF/A
Reeve Angel
934AH
(Acid Washed)
Gelman AE
(Acid Washed)
Conditioning Mass Before Mass After
Batch Number of 47 mm Time Conditioning Conditioning
Number Filters Conditioned (hours) (grams) (cjrams)
3307 20
8204 20
8192- 20
20232
3563 20
3307 20
8204 20
8192- 20
20232
3563 20
4292 20
8206 20
26 2.1888 2.1881
26 2.6644 2.8735
26 2.6717 2.8160
26 1.7695 1.8349
26 2.2149 2.2166
26 2.6266 2.8375
26 2.6522 2.8051
26 1.7361 1.8272
18 2.0968 2.0975
18 2.6939 2.7699
Mass Gain
per Filter Mass Gain
(mg) (percent)
-0.04 -0.03
10.46 7.84
7.22 5.40
3.27 3.70
0.09 0.08
10.55 8.03
7.65 5.77
4.56 3.64
0.04 0.03
3.80 2.82
a.  1%  S02, 3-5 ppm SO3,  saturated H20,  220°C (428°F).
b.  Filter materials are  listed in order of conditioning in a stainless steel Alundum thimble holder.

-------
                                                               TABLE 2.  SUMMARY OP FLUE  GAS TEST RESULTS.   THE FLUE GAS  TEMPERATURE  AVERAGED
                                                                   ABOUT 149°C  (300"F) FOR ALL  TESTS,   IMPACTOR FLOW RATE WAS  0.7 acfm
V£>
Substrate
Set
1
(Apiezon L)
Grease on
Substrate,
mg
Stage
0
1
2
3
4
5
6

Back-up



Blank
25.
13.
38.
11.
39.
12.


05
48
33
93
36
06

	
D
P
D
P
D
P

-
Mass Change
mg

+0.23
-4.96*
-7.29*
-27.98*
-0.64
-24.188
-0.35
b
+0.15
*

2
(Apiezon L)
Grease on
Substrate


mg

Blank
19.8
54.1
73.0
5.3
61.4
2.9

o.r
35
7
37
9
23
3


.23 D
.51 P
.24 0
.14 P
.23 D
.69 P

'

4a^s Change
ag

+0,
-3.
+0.
-28
+0.
-13
+0.

+0.

13
25a
33
.54*
15
.OS3
34
b
17
*

3
(Apiezon M)
Grease on
Substrate,
Mass Change
Jig nig


BUnk
9.2
4.4
71.3
1.6
44.6
3.9
£
0.2
21.
3.
19.
4.
26.
7.


69 D
19 t
03 D
36 P
09 D
10 P

	 __

i-O.
-0.
+0.
-7.
+0.
-10
-0.

+4.

08
02°
04
14°
10
,11°
05
a
40
4

_
0.1
1.3
37.5
2.3
38.8
0.7
f
3.1
4
(Apiezon T)
Grease on
Substrate, t


B:
23.
1,
3,
24,
24,
3,


tog

Lanfc
.63 D
.89 P
.25 P
.87 D
.78 D
.69 P

"
lass Change
mg

+0.
-1.
-0.
-0.
-0.
-1.
+0.

+5.

04
10°
25
21
61
07C
09
A
13
»

5
(Apiezon H)e
Grease on
Substrate


mg

Blank
4.6
13.2
6.5
2.5
4.3
2.4
f
3.6
41
4
3
28
30
4


.55 D
.18 P
.31 P
.04 D
.13 D
.87 P

-
, Macs
Change
mg %

+0.
+1.
+0.
K>.
+0.
+0.
-0.

+4.

01
56
82
80
44
53
05
•,
36


6
(Apiezon N)
Grease on
Substrate,
mg


Blank
3,
19
21,
1
1.
1,

3,
.8
.6
.0
.6
.8
.0
-
.0
19.19
4.41
19.00
3.37
18.79
4.14

"•
D
P
D
P
D
P


Mass
mg

+0
-1.
+0.
-1.
-0.
-1.
-0.

+4.

.03
52°
05
75
06
73°
10

74
Chan
1

.
8.
1.
9.
1,
9.
2.

3.
              a.  Greaae lost to overflow,  not recovered.
              b.  Beeve-Angel 934AB Filter  Material, preconditioned.
              c.  Some grease lost to overflow, most recovered and deposited back on foil.
              d.  Gelman AE Filter Material,  preconditioned.  Weight  gains may be partially due to flue gas reactions.
              e.  Substrates contaminated with ambient dust, but probably not enough to alter  results significantly.
              t.  Percent mass change in filter calculated using final filter weight.

              Note:   D means that the grease-toluene mixture was dropped on with a medicine dropper
                              (20 to 25 drops).
                      P means that the grease-toluene mixture was painted on with a small camel's  hair brush
                              (3 to 4 times).

-------
program of Apiezon H was run at a coal-fired power plant:   re-
sults are given in Table 3.  As a result of these tests,  Apiezon
H grease was approved for use in IERL-RTP programs for  tempera-
tures up to 177°C (350°F).

     The complete results of this study can be found  in EPA
report "Inertial Cascade Impactor Substrate Media for Flue  Gas
Sampling," EPA-600/7-77-060 (NTIS  No. PB 276583).

     This paper has briefly reviewed the development  of the use
of collection substrates in cascade impactors.  We will continue
to monitor operational procedures for impactors and recommend
techniques to satisfactorily use them; such as "Procedures  for
Cascade Impactor Calibration and Operation in Process Streams,"
EPA-600/2-77-004  (NTIS No.  PB 263623), currently being  used by
IERL-RTP personnel and contractors.
       TABLE 3.    APIEZON  H BLANK MASS GAINS  FOR UNIVERSITY OF
        WASHINGTON MARK III  SOURCE TEST CASCADE IMPACTORS3

Stage
0
1
2
3
4
5
6
Filterb
Run 1
5/17/76
0.22
0.06
0.04
-0.03
0.02
-0.06
-0.14
-0.32
Run 2
5/17/76
0.08
0.09
0.01
-0.11
-0.08
-0.13
-0.12
-0.18
Run 3
5/19/76
0.16
-0.18
0.04
0.09
0.09
0.05
0.13
0.02
Run 4
5/20/76
0.55
0.11
0.10
-0.13
-0.05
-0.03
-0.05
0.08
Run 5
5/21/76
0.65
0.85
0.64
0.64
0.47
0.31
0.16
0.34
X
0.33
0.19
0.17
0.09
0.09
0.03
-0.004
-0.01
a
0.25
0.39
0.27
0.32
0.22
0.17
0.14
0.25
 a.   Coal-fired power  boiler  source,  cold  side  precipitator
     operating at 107°C (225°F),  30 minute runtime.   All masses
     in milligrams.

 b.   Reeve Angel 934AH 47  mm  disc.
                               300

-------
                             PAPER 14
                 PARTICLE SIZE MEASUREMENT FOR THE
                    EVALUATION OF WET SCRUBBERS
                          SEYMOUR CALVERT
                        RICHARD CHMIELEWSKI
                          SHUI-CHOW YUNG
                  AIR POLLUTION TECHNOLOGY, INC.
INTRODUCTION
     Under the sponsorship of the EPA, A.P.T. has performed per-
formance tests on several industrial scrubber systems to obtain
data on the fine particle collection efficiency of air pollution
control scrubbers.  The scrubber performances in different situa-
tions are reported in terms of grade penetration curves and the
A.P.T. cut/power relationship.1  This  information was used to
evaluate the scrubbers and to verify,  improve and develop design
equations for the scrubber systems.

     The measurement of the size of small wet particles presents
unique problems which were not entirely appreciated until recent
studies were specifically conducted towards these measurements.
This paper presents our experience with this problem including
possible errors due to evaporation of  water from the particulate
as well as a single stage impactor design which has proved satis-
factory,

PARTICLE SIZE DISTRIBUTION MEASUREMENTS

     The most important experimental measurements in the perfor-
mance tests are those regarding particle size and concentration
in the inlet and outlet of the scrubber.  For accurate determina-
tion of particle size distribution, the measuring devices should
be able to measure the particles as they exist in the scrubber.
The devices should cause neither formation of particles nor break-
up of aggregates.  Cascade impactors are the most commonly used
particle classifier in scrubber performance tests.

     In a cascade impactor, particles  are classified by inertial
impaction according to their mass.  The larger ones are collected

                               301

-------
on the plate opposite the first stage and smallest  on  the  plate
opposite the last stage.  Cascade impactors  are  found  to be use-
ful for measuring dry particle size distribution and concentra-
tion for particles with diameters from a few tenths to several
microns.

     In the outlet of a scrubber the particles are  usually wet.
Even though cascade impactors have been used for  particle  frac-
tionation at the scrubber outlet, there is doubt  whether the
measured size distribution is representative of  the wet  particle
size distribution leaving the scrubber.  This doubt surfaced
when we tried to measure the "grown" particle size  distributions
in flux force/condensation scrubbers with cascade impactors.

     Flux force/condensation (F/C) scrubbers utilize diffusio-
phoresis, thermophoresis and condensation of water  vapor to im-
prove particle collection.  A.P.T. has operated  an  F/C demonstra-
tion plant as well as several pilot plants.2  5   Particle growth
due to condensation of water vapor was demonstrated by the im-
proved performance of the scrubbers as well  as by observation
of condensation clouds.

Wet Particles

     Measurement of the grown particle size  distribution with
multistage cascade impactors indicated some  growth; however,
the measured size distributions were not as  large as predicted.
The particles act as condensation nuclei and are  predicted to
grow to a size which is dependent upon the amount of water con-
densed and the number of particles present.   In  typical  applica-
tions the problem becomes one of measuring wet particles with
an aerodynamic diameter on the order of 1 ymA.

     It was suspected that evaporation of water  from particles
occurred inside the cascade impactor due to  the  pressure reduc-
tion from stage to stage.  To study the evaporation from par-
ticles within the cascade impactor we used the experimental ap-
paratus shown in Figure 1.  A 5% by weight sodium chloride solu-
tion was atomized using a Collison atomizer.  The gas  was  mixed
with dilution air which passed through a conditioner which either
humidified or dried and heated the dilution  air.  The  aerosol
was then passed through an impactor to obtain size  distribution
data.  A specific ion probe for Cl was used  to determine the
mass of salt collected  in these experiments.

     The first part of  the experiment involved drying  the  aerosol
generated by the atomizer by mixing it with  dehumidified and
heated dilution air.  The size distribution  obtained was that
of the dry residual salt particles.  Observation of the  substrates
indicated that no moisture was present for these runs.  Figure
2 shows the size distribution obtained for the dry  particles.


                               302

-------
                                     DILUTION AIR
                                     CONDITIONER
ATOMIZER
                                                                         PRESSURE  *7
                                                                         REGULATOR A
                                                                                    I
                                                                               COMPRESSED
                                                                               AIR
                        Figure 1.  Sketch of experimental equipment.
                                          303

-------
    8.0


    6.0



    4.0
 d
•o
of  2.0
HI
Q
UJ

g  1.0
OC
a  0.8
    0.6
    0.4
5% SALT SOLUTION
dpg = 1.7
                     O
    0.2
                        10
                 20
                                         40
                                       WT%
-------
     The size distribution of  the  parent  wet  particles  can  be
obtained from the size distribution  of  the  residual  salt  par-
ticles since the initial  salt  concentration is  known.   The  initial
drop diameter is related  to  the  salt particle diameter  by the
following equation:
                          dd  =  dp

where: d,   =   wet  particle physical diameter,  pm

       d    =   salt particle  physical diameter, ym

        p   =   salt density,  2.16 g/cm3

        c   =   salt concentration in solution,  weight fraction

      This  equation is good for diluted  salt solutions where the
density of the solution is close to that of pure water.   The
predicted  wet particle size  distribution is shown in Figure 3.
Note  that  the aerodynamic diameter is shown and that conversion
to physical diameter is required for application of equation
 (1).   Also shown on this figure are lines which represent size
distribution  which would exist if a given fraction of the water
were  evaporated from each of the particles.  The upper curve
shows the  parent wet particle  distribution while the lowest curve
represents the measured dry  size distribution.

Wet Size Measurement

      The  second part of the  experiment  involved measurement of
the wet drop  size distribution.  For this case the dilution air
was first  saturated in a fritted disk bubbler  so that particle
drying would  not occur.  The results of several sampling runs
with  the University of Washington cascade impactor are shown
in Figure  4.   As can be seen,  the wet size distribution, instead
of being close to the predicted parent  wet particle size distri-
bution,  is close to the size distribution of dried salt residues.
This  indicated that evaporation from particles occurred.  Since
the air was saturated with water vapor, evaporation from par-
ticles could  not occur before  the cascade impactor.  Thus, it
could be deduced that evaporation occurted within the cascade
impactor.

      To verify that evaporation did not occur  before the cascade
impactor,  a second series of experiments were  conducted using
a  series of glass impactors  which allowed observation of the
jet and  impaction plate.  Figure 5 shows the experimental setup.
Each  glass impactor consisted  of one jet.  By properly selecting
the jet diameter,  the pressure drop across each stage could be
kept  at a  minimum.
                               305

-------
8.0 -
                              •RY SALT - 108% EVAPORATION
0.4 -
             5     10     20
40      60
                                    WT%

-------
    10
    5.0
=*•   1.0
 a
•o
   0.5
   0.1
        II Mini	1—I   I   I   I   i
                       /o  /

                        *&*
                   /    ~x
        PREDICTED Q      /
        PARENT  /        '
        DROPS
                          ,        /
                  /
               ?'
            /
                   /  DRY SALT
-  I*/
                   GLASS IMPACTOR DATA
           /              A
                             D
           >                 O
                             U. of W. IMPACTOR DATA
        I 1
I.M.I     I   ,   I   .   I   |   I     I
      2    5   10    20     40    60     80   90



                     WT% UNDERSIZE, %



      Figure 4. Measured wet size distribution, U. of W. impactor

            and series glass impactor.
                        307

-------
                HEATER
ROTAMETER
    FILTER
 PRESSURE
 REGULATOR
                        P  T
                                                 P  T

— >





^^

A


F
IL1
_L_
TO
VACUUM PUMP
PER
                               STAGE 1    STAGE 2    STAGE 3
    COMPRESSED
    AIR
ATOMIZER
                  Figure 5. Experimental setup for glass impactors.

       A solution of 5% by weight salt  was  atomized.  The aerosol
  was dried by mixing it with heated  dilution air.  The dry salt
  size distribution confirmed the previously  obtained dry size
  distribution from the University  of Washington cascade impactor.

       Several runs were then run without dilution air.   The results
  are shown in Figure 6 along with  the  predicted wet particle size
  distribution.  As can be seen, there  is a reasonably good fit
  between the glass impactor data and the predicted wet particle
  size for diameters below 3 ymA.   There is slight deviation for
  drops larger than 3 ymA in diameter.  The parent drop size dis-
  tribution was calculated from the dried salt distribution measured
  with the University of Washington cascade impactor.

       The wet size distribution measured with the University of
  Washington impactor differs from  that of  the glass impactors
  for particles smaller than 3 ymA  in diameter.   The agreement
  between the two for larger particle sizes is fairly good.  Ap-
  parently, significant evaporation from small particles occurred
  within the University of Washington impactor.   The results shown
  in Figure 4 show that particles of  1  ymA  in diameter have their
  diameters reduced to 0.6-0.7 ymA  by evaporation.

       The reason for the evaporation from  the particles is probably
  due to the pressure reduction in  the  cascade impactor.  The pres-
  sure drop across the glass impactor was  relatively low.  There-
  fore, little or no evaporation  from particles occurs and the
  measured wet particle size distribution  is  close to prediction.
                                 308

-------
    8.0
    6.0
    4.0
O  RUN 7/2L
A  RUN 7/3L
D  RUN 7/4L
O  RUN 7/5L
•  RUN 7/8L - DRY
                               WET
    2.0
             PREDICTED PARENTS
E
3.
    1.0
    0.8

    0.6

    0.4

                     OAd
/
     .;

                                             /   00
                                                 SALT PARTICLES
                                              AVERAGE Ap cm w.c.
                                              WET           DRY

                                            AP2 = 1.8        1.0
                                                  7.1        67
    0.2
                                  I
                             II	I
                 5    10     20       40      60       80    90    95
                                         WT%
-------
Pressure Drop

     Another observation made in the lab and field experiments
is that the pressure drop experienced in a cascade impactor  is
generally larger for wet particles than for dry particles  for
comparable loading and sampling rates.  This is usually  attributed
to a higher pressure drop across the final filter if water  is
present.  Careful measurement of stage to stage pressure drop
in the glass impactor shows a higher pressure drop for wet  par-
ticles than for dry particles as shown in Figure 6.

     The results of these experiments show that the size distri-
bution of small wet particles (>3 ymA) obtained with a cascade
impactor can be in error due to evaporation of water from  the
particles as they experience successive pressure reductions  pass-
ing through the impactor.

Single Stage Impactor

     A single stage impactor has been used in order to get  data
on the size of the grown particles in an F/C system.  The objec-
tive of the single stage device was to minimize the pressure
reduction and the evaporation time.  The initial sizing system
was composed of a Greenburg-Smith impinger with a nozzle size
and sample flow rate chosen to provide a cut point in the area
of interest.  The impinger was followed by a total filter so
that a single cut point was obtained.

      In one application  the predicted grown particle size  dis-
tribution  indicated that a minimum particle diameter on  the  order
of 0.5  ymA  should occur  with a given amount of condensation.
Figure  7 shows the data  obtained with the single stage impactor
as well as  the initial particle size distribution and predicted
grown size  distribution.  These data demonstrate that small  wet
particles could be measured if enough care is taken and  the prob-
lems  are recognized.

Entrainment Measurement

      A  related problem in determining the performance of wet
scrubbers  is measurement of entrainment.  Scrubbing involves
the energetic  interaction of the gas stream and the scrubbing
liquid.  Entrained drops containing  suspended or dissolved  solids
can cause  excessive particulate emissions.  The contribution
which liquid entrainment makes to particulate emission can vary
widely  from system to system.  There  is no clear cut boundary
separating  "wet" particulate from entrainment; entrainment will
generally  be larger  in size ranging  from about 10 um to  several
millimeters in diameter.  The advantages and disadvantages of
three common methods  for measuring entrainment are briefly dis-
cussed  below.
                               310

-------
             2.0
             1.0


             0.8



             0.6




             0.4
             0.2
                        1     I
I    I    I   I   I    T
                                       INITIAL SIZE
                                          I    I   I   I
                             10    20  30

                                WT%
-------
     The second method is to use a cascade impactor.  This  can
produce correct results for drops larger than a few microns.
However, many of the commercially available impactors have  cut
points which are below the range of interest for entrainment
measurement, i.e., for drops with diameters larger than  20  urn.

     The third method for entrainment measurement is a hot-wire
anemometer.  An electrically heated wire is placed in the gas
stream.  Drops hitting the wire will attach to the wire, evapo-
rate, and cool the wire.  The amount of cooling is dependent
on the drop size and is detected by monitoring the resistance
of the wire.  The hot-wire anemometer can yield information on
drop size distribution as well as drop concentration.  However,
we found the hot wire to be very fragile.  It could not  detect
large drops accurately and there were calibration problems.

CONCLUSIONS

     The cascade impactor is useful for measuring dry particle
size distribution and concentration.  It has a useful range of
diameters extending from a few tenths of a micron to several
microns.  Due to evaporation of liquid from particles it is not
generally suitable for measuring small wet particles.

     A single stage impactor can provide information on  the size
of wet particles more accurately than a cascade impactor.

     Liquid entrainment drop size distribution and concentration
can be measured with hot wire anemometer, impactor and chemical
stain methods.  None of these techniques gives completely satis-
factory results.  Better techniques are needed.

ACKNOWLEDGEMENT

     The work upon which this paper is based was performed pur-
suant to Contracts 68-02-2124 and 68-02-2191 with the Environmen-
tal Protection Agency.

REFERENCES

 1.  Calvert, S., et al.  A.P.T. Field Evaluation of Fine Par-
     ticle Scrubbers.  Presented at the Second Fine Particle
     Scrubber Symposium, May 2-3, 1977, New Orleans.

 2.  Calvert, S., et al.  Feasibility of Flux Force/Condensation
     Scrubbing for Fine Particulate Collection.  EPA 650/2-73-
     036, U.S. Environmental Protection Agency, Research Trianale
     Park, NC, 1973.  NTIS PB 277307.              ^<"cn iriangie
                               312

-------
3.  Calvert, S., et al.  Study of Flux Force/Condensation Scrub-
    bing of Fine Particles.  EPA 600/2-75-018, U.S. Environ-
    mental Protection Agency, Research Triangle  Park, NC, 1975.
    NTIS PB 249297.

4.  Calvert, S., et al.  Improved Design Method  for Flux Force/
    Condensation Scrubbing.  Presented at  the Second Fine Par-
    ticle Scrubber Symposium, May 2-3, 1977, New Orleans.

5.  Chmielewski, R., et  al.  Flux Force/Condensation Scrubbing.
    Presented at the Engineering Foundation Conference, November
    1977, Monterey, CA.

6.  Chilton, H.  Elimination of Carryover  from Packed Towers
    with Special Reference  to Natural Draught Water Cooling
    Towers.  Tr. Inst. Chem. Eng. 30:235,  1952.
                                313

-------
                             PAPER 15
           EVALUATION OF PERFORMANCE AND PARTICLE  SIZE
                DEPENDENT EFFICIENCY OF BAGHOUSES
                            D.S.ENSOR
                           R.G. HOOPER
                           G.  MARKOWSKI
                    METEOROLOGY RESEARCH,  INC.

                               AND

                            R.C. CARR
                ELECTRIC POWER RESEARCH INSTITUTE
ABSTRACT.
     Baghouses have several operational characteristics which
should be considered during field testing.  These factors are
high collection efficiency, variation in pressure drop and outlet
concentration due to bag cleaning, integrity of the bags, and
the operation of the emission source.  Real time aerosol instru-
mentation at both inlet and outlet, gas monitors and pressure
transducers, all logged on a common time base, are used to track
the dynamic behavior of both baghouse and source.  Any effect
of mismatch in sampling times between inlet and outlet manual
sampling trains can be evaluated with the real time data.  A
light scattering detector installed at the outlet is also useful
in detecting operational problems, such as bag leaks and valve
malfunctions.  Experience has shown that a systems approach,
including both source and baghouse, is required for a meaningful
evaluation.

INTRODUCTION

Background

     Baghouses are capable of unusually efficient collection
of particulate matter.  Compared to other types of gas cleaning
                               314

-------
equipment, baghouses are  relatively independent of the composi-
tion and size distribution  of  the  material collected.   As  emis-
sion particulate mass  limitations  become  more  stringent and
"clear stack" opacities are required,  baghouses will  have  greater
application.

     In the past there has  been  little incentive to study  the
details of fabric  filtration because of the more than  adequate
collection efficiency.  However, with  the potentially  large  scale
application to electric power  utilities,  the basic data needed
to optimize baghouses  on  full  scale units must be obtained in
an effective manner.

Objectives of Paper

     The objectives of this paper  are  to  describe test techniques
and approaches used to measure the detailed performance of full
scale baghouses.   The  major emphasis is on measuring particle
size dependent penetration  or  collection  efficiency.   The  actual
test methods for particle sizing may vary depending on site
specific problems.  The details  of organization and management
of a large test group  using state-of-the-art methods  in a  remote
location will not  be discussed.

     The techniques described  in this  paper have evolved in  pro-
jects performed by Meteorology Research,  Inc.  for the  Electric
Power Research Institute.  The objectives of these studies have
been the complete  evaluation of  specific  gas cleaning  equipment.
A systems approach utilizing continuous monitoring instrumenta-
tion during the field  testing  and  a parallel engineering study
of costs and maintenance  problems  has  resulted in an  integrated
analysis of the technology  for specific installations.

TEST STRATEGY

Description of Baghouse

     Baghouses have unique  aspects when compared to other  gas
cleaning equipment.  A cut  away  drawing of a baghouse  is shown
in Figure 1.  The  dirty air enters through a duct at  the hopper
level.  The gas is filtered through the bags and the  cleaned
gas exists through ducts  at the  top of the baghouse.   The  bags
are attached to the cell  plate.  Baghouses are usually arranged
in individual compartments. Each  compartment  has valves allowing
isolation for cleaning with a  reverse  flow of  air or  mechanical
shaking of the bags.   The compartments may be  cleaned  on a timed
cycle or when a limiting  pressure  drop is reached. Bags are
typically 20 to 35 feet long and 12 inches in  diameter. A wide
variety of fabrics may be used for bag material.  Fiberglass
fabric coated with graphite or Teflon  to  reduce wear  is the  usual
choice for utility boiler bags.
                                315

-------
     Other designs  of baghouses  include filtration of  the gas
on the outside  of  the bags or the  use  of fabric panels instead
of bags.  However,  baghouses have  in common the removal of par-
ticulate matter by  filtration of the gas through a fibrous ma-
terial and provision for cleaning  the  filtering material when
the pressure  drop  becomes excessive.
                            DAMPER SHUT
       CLEANING
       BLOWER
     DAMPER OPEN
    SHAKING
    MECHANISM
                       $#  DUSTY
                       wf.7  INLET
• TO EXHAUST FAN

DAMPER OPEN
                       Figure 1. Typical baghouse.
                                316

-------
Test Considerations

     There are several  aspects  of  baghouse  behavior  which  should
be considered during  a  field  test  of  a baghouse.   Failure  to
consider the following  items  during  the development  of  a test
plan may yield misleading  data.

     Inspection—The  integrity  of  the bags  and  cell  plate  is
monitored for interpretation  of the  test results.  For  example,
leaks could mask effects of bag cleaning and  gas  flow  in a full
scale unit.  Samples  of new and used  bags should  be  obtained
for laboratory testing.

     High efficiency—The  very  efficient collection  capabilities
of fabric filtration  place a  heavy demand on  the  ability to mea-
sure gas streams with a 10,000  fold  difference  in  particulate
concentration.  The outlet concentration of a baghouse  can be
as low as 0.0001 grains/ft2.  Thus,  long sampling  times with
high flow rate test equipment and  very sensitive  instrumentation
are required.  Also special test and  data reduction  schemes are
required to compute particle  size  dependent penetration under
these conditions.

     Batch process—Baghouses effectively behave  similar to a
"batch process" because of the  need  to clean  the  collected par-
ticulate matter from  the fabric when  the pressure  drop  becomes
excessive.  The outlet  emissions will vary  as compartments are
removed from service  and cleaned.  During the test program, the
cleaning cycle must be  verified.

     Time constants—The response  of  a baghouse is not  instanta-
neous and in some cases several days  could  be required  to  obtain
steady operation.  The  slowest  changing parameters are  those
dependent on the ash  layer in the  bags.  New  bags  require  several
weeks of conditioning to reach  a stabilized collection  efficiency
and pressure drop.  Process changes  will introduce a time  lag
before steady conditions in pressure  drop and collection effi-
ciency are reached.

Effects of Fabric Particulate Matter  Loading  on Baghouse
Performance

     The basic filtration  parameters  are the  pressure  drop and
collection efficiency as a function  of particle size.   Both of
these are dependent on  the properties of the  collected  ash cake
and the supporting fabric.  The pressure drop mechanisms are
best understood and will be used here for illustration  of  the
effects of ash loading  on  the filter.

     The pressure drop  through  a fabric filter  is usually  de-
scribed by the following equation
                                317

-------
     AP = S Q/A

where AP is the pressure drop through the  supporting  fabric and
ash layer, S is the drag, Q is the volumetric  flow  rate,  and
A is the filter area.  The parameter Q/A is often called  the
air-to-cloth ratio, or face velocity.  The drag  is  usually re-
lated to the fabric areal loading w by a number  of  equations,
including the linear form suggested by Robinson  et  al.,l

     8 = 5,-, + K2w
          £j
where SE is the effective filter drag and  K2 is  the specific
resistance coefficient for the dust.  A nonlinear model has also
been proposed by Davis et al.2 for the cake formation zone with
the form

     S = a w

where a and b are  regression coefficients.

     A drag versus loading curve is shown  in Figure 2.  An explana-
tion of the linear-nonlinear behavior has  been advanced by Dennis
et al.3 from laboratory  studies.  The drag behaves  in two stages
depending on the history of the filtration cycle.   Nonlinear
drag and the cake  formation occur during the stage  where  the
particles deposit  within the fabric.  When the fabric is  saturated
and the cake forms on the surface, then a  linear drag is  observed.
The nonlinear section is not truly a "cake repair"  behavior as
described in the earlier literature.1  Dennis  et al.lf have de-
veloped a pressure drop  model using the laboratory  observation
that ash tends  to  break  off in sheets or slabs during cleaning.
Therefore the filter cake is not homogeneous and has  areas with
behavior  in both Zones A and B.

     There are  a considerable number of expressions for the
specific resistance, K2.  One is the Kozeny-Carman  equation

     K2 =  (25/6) y  (1 -  e) S 2/£ne3                             (1)
                            c   f
where y  is gas  viscosity, e is the filter  cake porosity,  Sp is
the surface-to-volume ratio and &„ is the  particle  density.
K2 could be expected to  be a sensitive function  of  particle size.
However, the determination of K2 from experimental  data  indicated
a different dependence on particle diameter than predicted above
and a dependence on  face velocity.5

     At the present  time, the areal dust concentration cannot
be directly measured in  the field without  shutting  off the bag-
house and removing a bag.  An indirect method  to estimate the
bag loading is  to  estimate the loading from the  inlet concentra-
tion and cleaning  frequency.
                               318

-------
Measurable Parameters

     The measurable parameters  are  listed  in  Table  1.   In  the
typical full scale field  test as many  of these  parameters  are
measured as possible.

     The fabric measurements which  are performed  in the laboratory
are difficult to  relate to  the  operation of the full scale bag-
house.

	TABLE 1.  MEASURABLE PARAMETERS

Baghouse:

     Pressure drop

     Cleaning cycles

     Gas flow rate

     Temperatures

Fabric:

     Permeability

     Weight

     Weave

     Material

Plow Stream Properties, IN/OUT

     Particulate  concentration

     Particulate  size  distribution

     Opacity

     Gas composition

     Particulate  composition
                               319

-------
   c
   'E
   +j
   H-

   C3
   CO

   C5
   <
   cc
   Q
   O
   E
   m
        CAKE
        FORMATION
                      HOMOGENOUS CAKE DEPOSITION
TERMINAL
DRAG, ST
                                        AS
                                AW
                     DUST RESISTIVITY K2 = AS/AW
               -EFFECTIVE DRAG, SE

             -RESIDUAL DRAG, SR


          RESIDUAL FABRIC LOADING, WR
                    AREAL FABRIC LOADING, W, Ib/ft2
                    Figure 2. Fabric filter resistance curve.
MEASUREMENTS

Pressure Drop

     Pressure drop  is one  of  the  fundamental variables  describing
the operation of the baghouse.  During the fabric cleaning  cycles,
the pressure drop can be quite  variable as shown in Figure  3.
The pressure drop across individual modules during the  operat-
ing/cleaning cycle  is useful  to trouble shoot and interpret
operations.  Two items may complicate pressure drop data:

  .  The overall pressure  drop  data reported for full scale
     baghouses  is the flange  to flange value.  The overall  pres-
     sure drop  includes the pressure drop through the ducts and
     valves in  addition to the  pressure drop through the  fabric.
     Although the flange to flange pressure drop is significant
     in the design  of the  process, it cannot be related to  lab-
     oratory studies without  assumptions or independent measure-
     ments of the pressure drop through the baghouse due  to the
     components other than the  bags.

  •  Often only the peak pressure drop for the baghouse is  easily
     obtainable.  Although this pressure drop is important  for
     the fan designer, it  is  not  descriptive of the pressure
      £°?K  K°U!      filtering bags and depends on the design
     of the baghouse.                                         ^
out
be specifed
be specified.
                       data  tO  be  usefu1' the gas volume through
                 it  ^ Ope'atin9  cvde during measurement must
               Most modern baghouses are well instrumented for
                               320

-------
o
o
      12
      11
      10
       9
                           10
                           10
                           10
                           10
                           10
                           10
12
12
12
12
12
12
14
14
14
14
14
                                    14
          16
                                         16
16
16
16
     16
                                               10'
                                              18
         20
     18
     20
18
20
18
20
18
20
     18
                   20
        PRESSURE DROP ACROSS BAGHOUSE, in. W.G.
          Figure 3. Typical pressure drop trace.
                          321

-------
pressure drop measurement and  additional transducers can often
be added if needed.

Mass Concentration and Gas Velocity

     Flue gas velocity and mass  concentration are typically mea-
sured using EPA Methods 2 and  5,  respectively.

Particles Larger than 0.5 um

     Cascade impactors have been  used  for  source testing to
characterize particles larger  than 0.5 \an  for a number of years.
An example of early work was reported  by Pilat, Ensor and Bosch.6

     The impactor designed at  MRI to facilitate sampling of par-
ticulate matter in stacks is shown in  Figure 4.  The design is
a simple annular arrangement of  jet and collectors reported by
Cohen and Montan.7  The simple jet-collection plate geometry
has been thoroughly studied by many investigators (for example/
Marple and Liu8).  The use of  a  collection disc allows flexi-
bility in choice of substrates.   For example, either a greased
surface or a filter mat can be used to enhance  particle collec-
tion.  "0" rings under compression seal the jet plates and body
sections.
                                          NOZZLE
                                          FIRST STAGE
                 JET PLATE
           COLLECTION DISC
                                           "O" RING
                                         FILTER


                       Figure 4. Cascade impactor.

                               322

-------
     The performance  of  a  cascade impactor  is strongly dependent
on the surface on which  the  particles are collected.   The  two
most popular substrates  have been glass fiber filter  mats  and
greased surfaces.  A  greased surface is preferable  because glass
fiber filter mats sometimes  react with stack  gases  (Smith  et
al.9)  Also, Rao reported  that filter mats  have poor  collection
efficiency. 1 °

     A large number of materials  have been  screened as coatings
to enhance particle collection.   Apiezon-L  high-vacuum grease,
a high-molecular weight  hydrocarbon, had the  best properties
of the materials tested  in terms  of stability and particle ad-
hesion and  it has been used  in tests less than 300°F.

     The discs are then  weighed on a Cahn 4100 analytical  balance
to 0.01 mg.  Typical  weights of the discs are approximately 630
mg.  Weighing by substitution is  used to improve the  accuracy
of the weighing.  The discs  are stored in labeled 15  x 60  mm
petri dishes.

     Quality control  for the impactor tests include blank  runs
where filtered stack  gas is  sampled through the impactor to detect
chemical reactions with  the  collection surface.  In addition,
field controls are used  to verify the precision of  the weighing.

     The weighing precision  of the discs is consistently within
0.01 mg.  The weight  changes of the substrates when subjected
to filtered  stack gas are  typically less than 0.05  mg  for  flue
gas  from the combustion  of low sulfur coal.

     The wide mismatch  in  inlet and outlet  concentrations  (a
factor of typically  10•*)  precludes simultaneous impactor testing.
The  approach used is  a  series of  inlet tests  a few  minutes each
within the  time period,  several hours, of two outlet  tests.
Blank tests  at the inlet and outlet are also  conducted.

     The data is analyzed  with a  procedure  reported by Markowski
and  Ensor.11  The cumulative size distributions are fitted with
a numerical  interpolation  technique.  Differential  size distri-
bution curves are used  to  compute penetration.  Error  bounds
on both differential  size  distribution and  penetration are cal-
culated.

Submicron Particle Sampling

Electrical  Aerosol Size  Analyzer—

     The Model 3131  Electrical Size Analyzer  (EASA) manufactured
by Thermo-Systems, Inc.,  St. Paul, Minnesota, is the  only  com-
mercially available  instrument capable of measuring aerosol par-
                               323

-------
ticle size distribution in the 0.01 - 1.0 ym diameter  range.
The EASA consists of two inter-connected modules:  a  flow module
and a control module.  It was commercially  introduced  in 1973
and is a greatly improved version of the Model  3000  which was
commercially introduced in 1967.  The EASA  is described  in detail
by Liu, Whitby, and Pui12 and by Liu and Pui.

     The EASA, shown schematically in Figure 5,  consists of a
charger, an electrical mobility analyzer which  removes particles
smaller than a selectable size, and an electrometer  which measures
the electrostatic charge carried by the particles  which  pass
through the mobility analyzer.

     Aerosol is drawn into the EASA at a flow rate of  50 Jlpm,
of which 4 Jlpm is measured by the instrument, 1 Jlpm  is filtered
for use as charger sheath air, and 45 Jlpm is filtered  for the
mobility analyzer core air.  The diffusion  charger exposes the
aerosol to positive ions, which charge the  particles as  a func-
tion of particle size.  The charger sheath  air  prevents  particles
from entering  the ion source chamber where  they can  acquire ex-
cessive charges.  The 5 Jlpm of charged aerosol  (4  Jlpm  aerosol
+  1 Jlpm charger sheath air) enters the mobility analyzer through
an annular opening near the outer wall of the mobility analyzer,
separating the charged aerosol stream from  the  negatively charged
central rod.

     The particles are attracted toward the central  rod, the
smaller ones with high mobility depositing  near the  entrance.
Particles smaller than a certain size are collected, while larger
particles pass through.  The cutoff size depends on  the  voltage
on the central rod.  A high efficiency filter collects the larger
particles and  the associated current is measured by  an electrom-
eter.

     By cycling the central rod voltage through a  number of pro-
grammed steps, each of which represents a factory  precalibrated
particle size, one obtains a series of electrometer  current
measurements.  The higher current values occur  with  low  central
rod voltages and small particle cutoff sizes.   The difference
of electrometer current between two consecutive central  rod volt-
ages is a measure of the particle concentration within the cor-
responding particle size range.

     For field operation, the operator manually or automatically
steps  the voltage of the mobility analyzer  collector rod through
eleven  internally programmed steps and records  eleven  correspond-
ing electrometer current values, a procedure which requires about
two minutes.   Liu and Pui describe the calibration of  the in-
strument, including aerosol sensitivity as  a function  of size
and the collector voltage-particle size relationship.13
                               324

-------
                                                                                                                           CONTROL MODULE
                                                                                                                           ANALYZER OUTPUT SI8NAL-
                                                                                                                            DATA READ COMMAND - -
                                                                                                                            CYCLE START COMMAND -
                                                                                                                            CYCLE RESET COMMAND -
                                                                                                                         AEROSOL FLOWMETEH READOUT
                                                                                                                          CHARTER CURRENT READOUT
                                                                                                                          CHARGER VOLTAGE READOUT
                                                                                                                   AUTOMATIC HIGH VOLTAGE CONTROL AND READOUT
                                                                                                                   ELECTROMETER (ANALYZER CURRENT) READOUT
                                                                                                                   ..---- -TOTAL FLOWMETER READOUT
U>
                                              FORCES ££ BARTICLE
                                            f,»CLtCTROST»TIC

                                            ftf'ACROOYNAMIC DRAG
>> EXTERNAL ,
•  DATA   ;
•^ACQUISITION'

-i  SYSTEM  •
                                                                                                                                    TO VACUUM PUMP
                                                    Figure 5.  Flow schematic and electronic block diagram of
                                                                 the electrical aerosol size analyzer.

-------
Extractive Sampling—

     MRI uses dilution systems to precondition  the  stack  aerosol
to allow measurements with the EASA.  Inlet aerosols  to a bag-
house may require dilutions from 10 to 5000:1.   A coal-fired
utility boiler emission usually requires from 100 to  200:1.
In a typical system the aerosol is sampled through  an impactor
precutter through a heated line into a three-stage  diluter.
Each diluter consists of a venturi meter for the aerosol, an
orifice meter for the dilution air and an orifice plate dilution
chamber.  An in-stack diluter is used at the outlet of  a  control
device where dilutions of up to 20:1 may be required.   The emis-
sions from a baghouse may be so dilute that only a  diffusional
dryer may be used to remove the water from the  emissions  to  pre-
vent condensation in the particle measuring instrument.

Opacity

Plant Process Visiometer—

     The real time measurement of the inlet and  outlet  opacity
is very useful to monitor the operation of the  baghouse.   The
outlet opacity is a sensitive indication of problems  such as
broken or leaking bags or valve leaks.  Also the outlet opacity
is important from a regulations standpoint.

It has been our experience that the emissions from  a  properly
operating baghouse are so dilute that the opacity may be  a few
tenths of a percent, which is below the detectability of  a stack
transmissometer.  A Plant Processing Visiometer,  a  hardened
integrating nephelometer, is used instead.

     A diagram of the instrument is shown in Figure 6.   The
aerosol is removed from the stack with a stainless  steel  probe
and  transported into the measurement chamber.   The  aerosol par-
ticles in the chamber are illuminated by a flash lamp with an
opal glass filter.  The scattered light is detected by  a  photo-
multiplier tube at approximately right angles to the  flash lamp.
The optics have been designed so that the output of the photo-
multiplier tube is proportional to the extinction coefficient
due  to scattered light.  The instrument is a physical analog
of the following equation:

                  ir

     bscat = 2 * f 3(9) sin e de
                               326

-------
           SAMPLE FLOW
   LIGHT TRAP
FLASH
LAMP
DIFFUSER
                                                     1L— - ELECTRONICS
PHOTO MULTIPLIER
                               ASPIRATOR
         Figure 6.  Diagram of the plant process visiometer (PPV).
                                327

-------
where

     h     = the scattering coefficient due  to  scattered light
      scat
      g(6) = volume scattering function

         9 = scattering angle

If there is no light absorption, the scattering coefficient is
identical to the extinction coefficient.   The extinction coef-
ficient is related to plume opacity with Beer's Law.
     Opacity  (percent) =  Fl - exp  (-bextL)J 10°
where

     b     = extinction coefficient, m"1
      ext

         L  = stack diameter, m

     The instrument  is spanned with an  internal calibrator con-
sisting  of an opal glass  lens of  known  scattering  coefficient.
The  lens is mechanically  placed  in the  view  of  the detector for
calibration and  retracted into a  sealed chamber between cali-
brations.  The PPV is described  in detail  by Ensor et al.1"1

     Two aspects of  the PPV performance are  shown  in Figure 7.
The  ability to adjust the gain over a wide range permits the
use  of  two units: one to  characterize the  incoming ash and one
to monitor the outlet of  the baghouse.   The  outlet data indicates
the  sensitivity  possible  with the unit.  The Freon 12 calibra-
tion point corresponds to a scattering  coefficient of 3.6 x 10~"m~1
 (8 mile  visibility,  0.036 percent opacity  on a  1-meter diameter
stack).

Gas  Sampling

     Continuous  gas  analyzers are preferred  to  manual sampling
for  monitoring utility boilers because  of  the ability to detect
upset  conditions.  The flue gas  must be conditioned before intro-
duction  to the instruments.  The  gas is withdrawn  from the stack
with stainless steel probes with  in-stack  filters.  The condensate
is removed in a  chilled dropout  jar.  Polypropylene tubing is
used to  transport  the gas to the  analyzers.   Multiple probes
at different  locations in the duct are  used  to  obtain a repre-
sentative  sample of  stack gas and to sample  for stratification.
On site  span  and zero gas are used to calibrate the analyzers.
Typically, 02, S02,  NO and CO are measured.   Orsat samples are
used to  check the 02, C02 and CO determinations.
                               328

-------
             OUTLET OF BAGHOUSE



                       100
uj
UJ
O
o
UJ
o
CO
     6.7< ID'3)




     4.9(10-3)





     3.1(10-3)




    1.26(10-3)



           0
UJ

o
\L
u.
UJ
O
O

(3


E
Ul
u
CO
   1.44(10^)




   0.96I10'1)




   0.48(1(r1)
           0 M
              INLET OF BAGHOUSE


                        100
                    1600     1500
                                   1400    1300    1200


                                     LOCAL TIME, hours
1100    1000     900
                  Figure 7. Example of PPV data taken at Nucla baghouse.
                                          329

-------
     The Goksoyr/Ross (G/R) controlled condensation  method is
used to measure SOa/HaSO^.  The stack gas  is pulled  through a
glass probe maintained at 450°F.  The particulate  matter  is re-
moved from the gas by filtration through a quartz  filter  main-
tained above 450°F.  At this temperature the S03 is  all  in vapor
phase and only particulate matter is removed.  A quartz  filter
is used to reduce conversion of S02 to S03.  The H2SCK  is then
removed in a condenser maintained at 140°F.  The condensate is
titrated with NaOH to determine the acid concentration.   The
method is accurate to 16 percent.15

Data Integration

     The numerous and diverse measurements performed on  a bag-
house pose some problems in assembling the information.   Our
approach to reduce difficulties in data analysis is  to  data log
all continuous output on a magnetic tape data  logger.   The single
time base allows correlation of the various parameters.   A sche-
matic of such an arrangement is shown in Figure 8.   In  this
scheme a central data logger is used with  backup strip  charts.
This arrangement allows a  field test control room  where  the test
parameters can be monitored from one location.

EXAMPLES OF DATA OBTAINED

Process Charts

     Process charts of the main parameters plotted on a  common
time basis are useful to determine the effects of  process changes
or  upsets on the baghouse-  An example is  shown in Figure 9.

Efficiency as a Function of Operating Parameters

     Ideally the test should include some  variation  of  air-to-
cloth ratio and the cleaning cycle to develop  the  limits  of
operating parameters.  An  example of variation of  emission with
air-to-cloth ratio is shown in Figure 10.  This information is
useful  for engineering design.

Penetration

     The cascade impactor  and EASA data are used to  compute the
particle size dependent penetration through the baghouse.  The
data reduction technique reported by Markowski and Ensorl* is
used for the cascade  impactors.  The EASA  data is  reduced by
computing an inlet and outlet size distribution and  dividing
the outlet by the  inlet distribution.  An  example  of penetration
data obtained at a baghouse is shown in Figure 11.
                               330

-------
u>
         S TYPE PITOT
         PROBE WITH PRESSURE
         TRANSDUCER
                           I
                                                          GAS
                                                          ANAJ.YZERS
                                                          AND PANELS
                                                       I              TRAILER
                                                                                                            TEMPERATURE
GAS LINES
FROM SAMPLE
LOCATION BEFORE
AIR HEATER
                                              Figure 8. Integrated baghouse sampling system.

-------
   GENERATOR
   OUTPUT
   MEGAWATTS
                   11.0  11.0    11.0  11.0   10.7
                                                10.6
                                                       10.8   11.1   10.8
                                                         i      i     i
      SUBMICRON OUTLET
      PARTICLE   i	I
      TESTING
CASCADE IMPACTOR
INLET PORT NO.
CONCENTRATION
(103 mg/m3)
                        4   6

                      4.7   14.7
                                INLET INLET OUTLET   INLET
                                          1  4

                                        1.6  2.1
OUTLET
CONCENTRATION
M ill Uh -
4.0
3.0
s^
2.0 ^-
U.
r™
u
1.0 *
0.8
0.6
       Q.
       a
       O
       X
       O
      O
      CO
      cc
      5
           500
           400
          300
           200
          100
                                   CO CONCENTRATION
                                         (INLET)
                   1200  1300  1400  1500   1600   1700   1800  1900  2000  2100

                                       LOCAL TIME, hrs

         Figure 9.  Process variation during November 12, 1975 (Ensor et al. 1

                                         332

-------
V)
cc
X
Q
UJ
cc
111
UJ
Q
UJ
V)
O
00
X
O
O
cc
X

O
Ul
a.
    SYMBOL
LOAD MW
CLEANING
FREQUENCY
PRESSURE
DROP
BETWEEN
CLEANING
IN. W.G.
14
13
12
11
10
9

8
7
6
5
4
3
2
1
0
O 6 NONE 3.0
D 11 HOURLY 3-4.5
A 12 HOURLY-CONTINUOUS 3-4.5
-
-
-
i
™
-
-
-
T
T i
? I
J_ J-
DESIGN SIX COMPARTMENTS
-
-
-
-
-
-
k
-
-
-
-
-
-
-
7,"
99.86
99.87
99.88
99.89
99.90
99.91

99,92
99.93
99.94
99.95
99.96
99.97
99.98
99.99
                                                                     O
                                                                     UJ
                                                                          LL
                                                                          LL.
                                                                          Ul
0        0.5       1.0        1.5       2.0        2.5        3.0

AIR-TO-CLOTH RATIO BETWEEN COMPARTMENT CLEANING, acfm/ft2
      Figure  10.  Penetration as a function of air-to-cloth ratio with one
                 standard deviation limits (Ensor et al. 16),
                                      333

-------
   10
    I-2,-
UJ
CO
D
O
I
CQ

O

O
CC
I
CC
111
10-4
    10'5
        SULFURIC ACID
        NUCLEI
hHI
         OVERALL
         PENETRATION = 2.75 x 10'4
         EFFICIENCY = 99.973%
        NOVEMBER 14, 1975
        6 MW LOAD
        NO CLEANING CYCLES
        PRESSURE DROP 3.0 IN. W.G.
        •  ELECTRICAL AEROSOL SIZE
            ANALYZER
        D  CASCADE IMP ACTOR
        ONE STANDARD DEVIATION LIMITS
        PARTICLE DENSITY = 2.0 g/cm3
                                                            99.0
                                                            99.9
                                            O
                                            ID
                                            o
                                                             99.99
                                                         99.999
      0.01
0.10               1.00
                       PARTICLE DIAMETER,
                                                       10.0
      Figure 11.  Fractional penetration through baghouse (Ensor et a/.16).
                                 334

-------
SUMMARY

     The field measurements are complicated  by  the  variability
of the outlet particulate  concentrations,  the dilute  emissions,
the time required  to  obtain stable  conditions,  and  the  conditions
or the bags.  The  testing  of baghouses  is  facilitated with  the
use of continuous  instruments for both  particulate  matter and
trace gases, and data logging.

REFERENCES

 1.  Robinson, J.W.,  R.E.  Harrington, and  P.W.  Spaite.   Atmos.
     Environ. 1(11):499-508, 1967.

 2.  Davis, W.T.,  D.E.  Noll, and P.J. LaRosa.   A Predictive  Per-
     formance Model  for Fabric  Filtration  Based on  Pilot Plant
     Studies.  In:   Proceedings, User and  Fabric Filtration
     Equipment II,  Specialty Conference of the  Air  Pollution
     Control Association,  Niagara Falls,  1975.

 3.  Dennis, R., R.W. Cass, and R.R. Hall.   Observed  Dust Dis-
     lodgment from Woven Bags and its Measured  and  Predicted
     Effect on Filter Performance.   Paper  No. 77-32.3,  presented
     at the 70th Annual Meeting of  the  Air Pollution  Control
     Association,  Toronto, Canada,  June,  1977.

 4.  Dennis, R., R.W. Cass, D-W. Cooper,  R.R. Hall, V.  Hampl,
     H.A. Klenn, J.E. Langley and R.W.  Stern.   Filtration Model
     for Coal Flyash  with  Glass Fabrics.   EPA-600/7-77-084,  U.S.
     Environmental Protection Agency, Research  Triangle Park,
     NC, 1977.

 5.  Cooper, D.W.,  and V.  Hampl. Fabric  Filtration Performance
     Model.  In:   Proceedings,  Conference  on Particulate Collec-
     tion Problems in Converting to Low-Sulfur  Coals.   G.B.  Nichols,
     ed.  EPA-600/7-76-016, U.S. Environmental Protection  Agency,
     Research Triangle Park, NC, 1976.    pp. 149-185.

 6.  Pilat, M.J.,  D.S.  Ensor, and J.C.  Bosch.   Source Test  Cascade
     Impactor.  Atmos.  Environ. 4:671-679,  1970.

 7.  Cohen, J.J.,  and D.M. Montan.   Theoretical Considerations,
     Design, and Evaluation of  a Cascade  Impactor.  J.  Am.  Ind.
     Hyg. Assoc. 28:95-104, 1967.

 8.  Marple, V.A.,  and B.Y.H. Liu.   Characteristics of  Laminar
     Jet Impactors.   Environ. Sci.  Technol.  8:648-654,  1974.

 9.  Smith, W.B.,  K.M.  Gushing, and G.E.  Lacey.  Andersen Filter
     Substrate Weight Loss.  EPA-650/2-75-022,  U.S. Environmental
     Protection Agency, Research Triangle  Park, NC, 1975.
                               335

-------
10.   Rao,  A.K.   Sampling and Analysis of Atmospheric Aerosols.
     Particle Technology Laboratory, Mechanical Technology  De-
     partment,  University of Minnesota, Publication 269,  1975.

11.   Markowski, G.R., and D.S. Ensor.  A Procedure for Computing
     Particle Size Dependent Efficiency for Control Devices from
     Cascade Impactor Data.  Presented at the 70th Annual Meeting
     of the Air Pollution Control Association, Toronto, Canada,
     June, 1977.

12.   Liu,  B.Y.  H. , K.T. Whitby, and D.Y.H. Pui.  A Portable Elec-
     trical Analyzer for Size Distribution Measurement of Sub-
     micron Aerosols.  J. Air Pollut. Contr. Assoc. 24:1067,
     1967.

13.   Liu,  B.Y.H., and D.Y.H. Pui.  On the Performance of the
     Electrical Aerosol Analyzer.  J. Aerosol Sci. 6:249, 1975.

14.   Ensor, D.S., L.D. Bevan, and G- Markowski.  Application
     of Nephelometry to the Monitoring of Air Pollution Sources.
     Paper No.  74-110, presented at the 67th Annual Meeting of
     the Air Pollution Control Association, Denver, June, 1974.

15.   Maddalone, R.F., and N. Garner.  Process Measurement Pro-
     cedures-Sulfuric Acid Emissions.  TRW Report 28055-6004-
     RU-00 to Environmental Protection Agency, Contract No.
     68-02-2165, February 1977.  36 pp.

16.   Ensor, D.S., R. Hooper, and R.W. Scheck.  Determination
     of the Fractional Efficiency Opacity Characteristics,  and
     Engineering and Economic Aspects of a Fabric Filter Operating
     on a Utility Boiler.  MRI Final Report No.  FR-1411 to  Elec-
     tric Power Research Institute, Contract RP534-1,  1976.
                              336

-------
                              PAPER 16
    EVALUATION OF THE EFFICIENCY OF ELECTROSTATIC PRECIPITATORS
                          WALLACE B.  SMITH
                           JOHN P. GOOCH
                          JOSEPH D. McCAIN
                         JAMES E.  McCORMACK
                    SOUTHERN RESEARCH INSTITUTE

INTRODUCTION  AND  SUMMARY

     A system is  described  that can  be  used  to measure  the
particle-size distribution  in process streams at  control device
inlets and outlets  to evaluate their collection efficiency.
The fractional efficiency is  determined from 0.01 to  10 ym and
real-time systems are used  to discriminate transient  events and
nonideal behavior.

     Typical  results  are shown illustrating  particle  size distri-
butions and collection efficiency with  and without rapping.
It was found  in a series of tests that  rapping emissions may
constitute up to  80 percent of the total emissions; the higher
emissions are observed at hot precipitators.

EQUIPMENT AND PROCEDURES

     Figure 1 is  a  schematic  illustrating the operating principle
of electrostatic  precipitators.   Ions,  created near the high
voltage corona electrode,  attach themselves  to the aerosol par-
ticles which  in turn  are collected on the grounded plates by
electrostatic forces  as they  pass nearby.  Ideally, the collec-
tion efficiency of  a  precipitator can be made arbitrarily high
by increasing the residence time of  the aerosol  (the  precipitator
dimensions).

     As a layer of  collected  particles  accumulates on the grounded
plate, the plates are periodically "rapped"  to dislodge the layer,
which falls into  the  hoppers  below.  Sometimes a  fraction of


                               337

-------
                                    HIGH-VOLTAGE
                                    SUPPLY
  PLATE
  RAPPING
  SYSTEM
  DUST
  LADEN
  AIR
                                                     GROUNDED
                                                     COLLECTION
                                                     ELECTRODES
CLEANED
AIR
  CORONA WIRES
                                        DUST COLLECTION
                                        HOPPERS
         Figure 1. Schematic drawing of the electrostatic precipitation process.
the previously  collected dust is reentrained into  the  aerosol
stream to  be  recollected or to escape  into the atmosphere.  The
rapping  frequency and power are adjusted to minimize  such losses;
but, rapping  reentrainment is an important factor  in  limiting
precipitator  performance.

     A second,  nonideal factor that  influences precipitator per-
formance is "sneakage" or passing of a part of the  aerosol stream
through  areas where the particles are  not charged,  such as through
the hoppers,  or the electrode suspension areas.  Sneakage is
minimized  through the precipitator design.
                                338

-------
     Figure  2  shows curves illustrating  the nature  of  precipi-
tator fractional  efficiency; i.e., efficiency  vs. particle  diam-
eter.  Because of the relative electrical mobility  of  particles
of different sizes, the collection efficiency  is  highest  for
very fine and  very large particles with  a minimum value  for par-
ticles of approximately 0.5 pm diameter.  The  curves also show
how sneakage and  rapping reentrainment degrade the  performance
of the precipitator.  Sneakage allows particles of  all sizes
to penetrate the  precipitator, while rapping puffs  contain  pri-
marily large agglomerates of particles that were  collected.
Thus, rapping reentrainment should not be considered penetration
of the primary aerosol, but rather the creation of  a different
aerosol.  For proper evaluation of a precipitator performance,
it is desirable to isolate and identify  the emissions  due to
normal penetration, sneakage, and reentrainment.  Other,  more
subtle nonideal effects exist but are generally less important.

     Figure 3 shows the main objectives  of precipitator  evalua-
tion tests  and the requirements to achieve these  objectives.
For  even  the most rudimentary diagnostic tests it is necessary
to acquire  knowledge of the gas velocity distribution, the  main
gas  constituents, and characteristics of the dust such as ap-
proximate size distribution, concentration, and electric  resis-
tivity.   Also, the electric operating parameters  must  be  noted
and  an assessment of the mechanical condition  made. Tests  de-
signed to acquire data for research generally  require  more  tests
and  better  accuracy and resolution.
              100
            >-  90

            UJ
            O
            u.
            u]  80

            O
            o
            111
            O
            CJ
               70
               60
     • IDEAL PERFORMANCE
 	EFFECT OF SNEAKAGE
 	EFFECT OF REENTRAINMENT
               0.01
 0.1           1.0

PARTICLE DIAMETER, jum
                                                       10
             Figure 2. Typical precipitator performance curve showing negative
                   effects of sneakage and reentrainment.
                                339

-------
Assure Compliance Obtain Design
with EPA Optimize Performance Data for
Objective of Tests Regulation of Control Device Control Device
Tests Required
Mass Concentration 	
Opacity 	
Gas Composition 	
Gas Temperature 	
Gas Volume 	
Pressure 	 	
Velocity Distribution 	
Particle Size Distribution 	

Control Device Data
Operating 	



Technical Considerations
(Decisions/Problems)
Adequate Space,
Laboratory Space
Number of Tests Required
Isokinetic Sampling
Condensible Vapors/
Volatile Particles
Mass Concentration/
Sampling Time
Traverse Strategy
Aerosol Gas Velocity
Process/Emission
Variations
Select Particle Sizing
Method;
Select Mass Train Type
Select Gas Analysis Methods
Real-Time Monitors Needed 	
Filter Mass Stability
Sample Preservation ..


	 •
	
	












v
3
x

c
o
c
c

•0











P









v

x
r
P
0
P
P

o
fj
D
c
o

1

1
1
1
1
r
i
	 — Qualit3tiv6 — —






1
Y

V
P
P

P
P
1 ft
i n
'>«
n



for Modeling Process and
Studies Control Device
— in -

1 0
1 0
1 0-
1 0
x
1 0
— Qualitative 	
ESP only
v
x

D

1 0
V

Y
f
P



i n
	 I,U 	
i n



	

1 0
o
1 0
1 0
1,0
1,0
x
1 o
1 0*
x
x
x
x
o
x
i n
Y

. Y
,p
,, ... r



\ n
	 Ml
i n
I,U




Key:
-   Outlet
-   Inlet
-   Required
-   Decision based on specific site or test objectives
-   Must be considered
vs. Particle Diameter
                  Figure 3.  Objectives of precipitator performance evaluations and tests
                             required for completion.
                                            340

-------
     In Table 1,  the  participate  sampling  methods  used  by  South-
ern Research for  precipitator  analysis  are listed.   Cascade  im-
pactors are used  more than  any other  type  of  sampling device
for measuring particle-size distributions.  Modified Brink im-
pactors are used  when particle concentration  is  high (inlet)
and Andersen or University  of  Washington impactors  are  used when
the concentration is  lower  (outlets).   Greased foils are pre-
ferred as collection  substrates,  but  for temperatures above 300°F,
glass fiber filter material is used.

     If larger samples are  required for analysis, cyclones can
be used in a series arrangement to obtain  sized  particulate frac-
tions in quantities of several tens of  milligrams to several
grams.  The EPA/Southern  Research cyclone  system has five small
cyclones with D50's of 0.3,  0.6,  1.2, 2.5,  and 5.6  ym.

     Cascade impactors and  cyclones yield  samples that  are ac-
cumulated over periods of time ranging  from several  minutes to
several hours; thus,  the  size  distributions measured with these
devices are time  averaged.   Optical particle  counters may be
used to yield real time or  instantaneous data on particle concen-
tration and size.  Disadvantages  of these  counters  are:  1) They
are designed for  laboratory use,  and  the samples must be diluted
and cooled.  2)  They  do not  yield aerodynamic particle  size;
consequently, some knowledge (or  assumptions)  of the optical
properties of the dust must  be  known to calculate the aerodynamic
sizes from optical data.  Alternately,  the  optical particle
counters may be calibrated  for  the particles  of  interest to yield
aerodynamic sizes.  Marple1  has designed special impactors for
calibration of optical particle counters, while McCain2 has used
sedimentation to  perform  calibrations.  We  have  used the Climet
207 and Royco 225 optical particle counters in our  field test
programs.

     Figure 4 shows schematically an optical  particle sizing
system for large  particles  that is used to  count particles from
1-30 ym in five size  fractions.   In the diluter, the particles
pass from the inlet jet,  through  a turbulent  zone,  toward the
outlet jet.  Small particles are  deflected  more  than the larger
particles; thus a larger  fraction of  the large particles is
counted.  It is necessary to dilute the small particles to a
number that is within the range suitable for  the counter, but
the large particles require little or no dilution.   Figure 5
shows a special plugin unit designed  by Southern Research for
use with optical  particle counters.   It is  a  five channel  pulse
height analyzer.  The data  are seen as  analog readings  on the
front of the plugin,  and  also  analog  recorder outputs are pro-
vided for each channel.   Linear or logarithmic responses are
chosen by means of toggle switches on the  front  of  the  device.
The unit will plug directly into  the  Royco 225 optical  particle
counter, or can be used in  a special  chassis  with any optical
counter with which it is  compatible.


                               341

-------
   TABLE 1.  MAIN COMPONENTS OF THE  SOUTHERN  RESEARCH PARTICLE
                          SIZING SYSTEM
      Method
Size range (diameter, urn)
                                                   Remarks
Impactors
Cyclones
Optical particle
         a
  counter
Electrical mobility
  analyzer3

Diffusion batteries
  and condensation
  nuclei counters9
                             0.5 - 10
        0.3 - 6
        0.3 - 1.5
          1-30
        0.01 - 0.5


        0.01 - 0.2
Time-averaged
  sample

Time-averaged
  larger samples

Real-time data,
  not aerodynamic
  sizing

Time-averaged
  sample

Time-averaged
  size distri-
  bution; some
  time resolution
  possible
  Sample extraction and dilution required.
     For the ultra-fine particle size range (0.01-0.5 pm) elec-
trical aerosol analyzers (TSI Model 3030)  or diffusion batteries
with condensation nuclei counters are used.  Again, these are
laboratory instruments and sample dilution and cooling is re-
quired.  The diffusion batteries are the parallel plate type,
and are of our own design.  We have used General Electric, Gard-
ner, and Environment One condensation nuclei counters.

     A more detailed description of the procedures used to de-
velop and implement precipitator evaluation programs has been
given elsewhere.3

QUALITY ASSURANCE AND CONTROL

     Three important problems related to quality control of par-
ticulate sampling data have been addressed as part of our sam-
pling program.  Harris et al. have discussed the first problem,
the selection of suitable impactor substrates, in an earlier
paper of this symposium.  A second problem has been the formation
of a sulfuric acid fume in our sample extraction and dilution
system.  The formation of the fume is detected by a very non-
linear increase in submicron particles as the dilution factor
is reduced.  This phenomenon is observed at sites when the S03
concentration is high and when low dilution factors are  used.
                               342

-------
  SAMPLE
  FLOWRATE
  MANOMETER

s s
/ <
;<
<
ff
~/
•«*
**
•»
»
I
\
GAS FLOW

\
PROCESS EXHA
PRORF i IMC
HEATER
                                     DILUTION AIR
                                     MANOMETER
                                     AND ORIFICE
                                                       0.02 urn
                                                       FILTER
                                        BLEED
                                        VALVE
                                                                  ?=&=
                                          CONDENSER    FLOW
                                          POT         	'
                                                                      PUMP
                                        BLEED
                                        VALVE
VERTICAL
                                          ELECTRICAL
                                          LEADS, ETC.
                                                           LARGE PARTICLE
                                                           COUNTER
                                                           MAIN FRAME
                   Figure 4.  The large particle sampling system.
                                    343

-------
            Figure 5. A special pulse height analyzer plugin developed by
                   Southern Research Institute.
Figure 6 shows our  sample  extraction-dilution system with  dif-
fusion absorbers for condensible  gases.   The absorbers  consist
of stainless steel  cylinders,  with a smaller, screen cylinder
inside.  The void between  the  cylinders  is filled with  granular,
activated charcoal  and  the aerosol sample passes through  the
inner cylinder.  This technique has been very successful  at
eliminating the formation  of  fumes at sources when  the  SO 3 con-
centrations are quite high.

     A third potential  problem is  the distortion of particle
size distributions  by electric charges that exist on the par-
ticles, particularly at the outlet of precipitators.  An exten-
sive study of this  problem has been made and the results will
be published later.  Typical results, however, are  shown below.
                               344

-------
U)
ft.
en
^



CYCLOI
PUMP
ATED PROBE \
UJ
X
/
       PROCESS EXHAUST LINE


       CHARGE NEUTRALIZER

                   CYCLONE

ORIFICE WITH BALL AND SOCKET
    JOINTS FOR QUICK RELEASE
                                                         DUMP
                                                                                   TIME
                                                                                   AVERAGING
                                                                                   CHAMBER
                                                        BLEED          DILUTION DEVICE

                                                          CHARGE NEUTRALIZER
                                                                                             SIZING
                                                                                           H INSTRUMENT
                                      SOX ABSORBERS (OPTIONAL)
                                            HEATED INSULATED BOX


                                  RECIRCULATED CLEAN. DRY, DILUTION AIR
                                                                         FILTER   BLEED NO. 2
                                                                                              COOLING COIL
                                                                                                         PRESSURE
                                                                                                         BALANCING
                                                                                                         LINE
                                                                                                                DRYER
BLEED NO. 1
                           MANOMETER
                                          Figure 6. The sample extraction-dilution system.

-------
     Figure 7 shows one of the experimental setups  used  for  the
charged particle experiments.  Aerosols of 1.3, 0.69,  and  1.0
urn mass median diameter were generated in concentrations that
were comparable to those found in process streams by nebuliza-
tion.  The particles were passed through an electric corona
charging device, and into the test impactors  (Andersen impactors
with glass fiber substrates).  Polonium-210 devices were used
to discharge the particles in one aerosol stream and low voltage
ion precipitators were used to remove ions.  The cascade impactors
were used as Faraday cages and the charge accumulated  was  mea-
sured by electrometers.  Care was taken to insure that the aerosol
was properly split between the impactors and that losses in  the
sampling lines were minimal.  In all of the experiments  the
results were extremely reproducible, indicating a high degree
of precision.

     Typical results from the charged particle experiments are
shown in Figures 8 and 9.  In Figure 8 a 1.01 pirn mmd aerosol
was charged to approximately the value that would be acquired
in a conventional electrostatic precipitator.  The  level of
charge relative to a precipitator is indicated in the  figure.
Very little difference was found between the charged and un-
charged particle distributions.

     A highly charged aerosol was sampled and the results  plotted
in Figure 9.  In this experiment, a much larger, and significant,
difference was found in the charged and uncharged aerosols.
Experiments were performed with different impactors, different
substrates, grounded and ungrounded impactors, monodisperse
particles, and different charge levels.  Analysis of the results
is complete and a report is now being written (EPA Contract No.
68-02-2131).

     The results of the charged particle experiments indicate
that for moderate levels of charge, and where using glass  fiber
substrates, the interferences due to electrostatic charges are
small.  When sampling highly charged aerosols, however,  the  size
distribution can be distorted significantly.  Unfortunately  no
suitable charge neutralizing device is available for in-stack
use.
TYPICAL RESULTS OF PRECIPITATOR EVALUATIONS

     Figures 10 through 13 show results from field test measure-
ments illustrating the type of data that is obtained using the
systems described and their application to precipitator evalua-
tions and source characterization.
                               346

-------
           DISPERSION
           CHAMBER
                  DILUTION ROTAMETER
                     VALVE     DRYER
                                                          COMPRESSED AIR LINE
                      ATOMIZER
                                           ABSOLUTE
                                     VALVE F|LTER
                                  ATOMIZER ROTAMETER
                                                       REGULATOR
         *—  MIXING-DRYING COLUMN
                                             ELECTROMETERS

                                               Lj
                                                    CASQADE IMPACTORS

                                                            METERING ORIFICES
              DIFFUSIONAL DRYERS
                           ELECTROSTATIC SHIELD
PO210 CHAMBERS
           ION PRECIPITATORS
                           INSULATED
                           FROM GROUND
HIGH VOLTAGE
POWER  SUPPLY
                                         MERCURY MANOMETERS
                                                       WATER MANOMETERS
            Figure 7. Experimental setup for the charged particle investigations.
                                   347

-------
    1BIS7U  U>*0  KlflHUZBDIWCnK HUH. OWBB6
    M = U5»ff  EJOIttl»lH5IHIH .SHOW
10°
           I
                                 CHARGED
                                 NEUTRALIZED
H—I  I 1 IIH|	1—I I  I MM|	1	1  MIN
   1CT1         10°

   PARTICLE DIAMETER  (MICROMETERS)

   Figure 8. Particle size distribution for moderate charging conditions
          for a mass median diameter of 1.02 pm.
                     348

-------
      TEISlS-lfl  UHW KU1HU2ED UnciS

      M = L£HKC  GOJIEW9SLSIWM JSUQDG
101::
iff-
10'
                  »*».
                 s   V
 ^
!f
               •li
              **
             J*
              r
                        [*
                            *
                             L
                              i
                                   CHARGED
                                  NEUTRALIZED
 I  I I  Mill	1—I  I I III
                  10°
                      101
                                   H—I  I I Mill
   PAF?TICLE  DIAMETER  (MICROMETEF5S)



     Figure 9. Particle size distribution for high charging conditions
           for a mass median diameter of 1.01 /im.
                      349

-------
CO
ui
o
          1,000,000
      m

      |
       o

      <


      Q
      O
      CO
            750,000
            500,000
            250,000 —
                                                       A.
              	1	


O DIFFUSIONAL DATA PARTICLE DIA.  0.11 p

A OPTICAL DATA PARTICLE DIA. 0.35-0.6 urn
                                               10
            20

  TIME, minutes
                                                                                                        30
                                    Figure 10.   Particle concentration versus time in the effluent
                                                from an asphalt batching process.
                                                        20,000
                                                        15,000
                                                                                                                                 o
                                                        10,000   p
                                                                 o.
                                                                 O
                                                        5,000

-------
                                                                                                                17 um AND LARGER PARTICLES


                                                                                                                  I     I    I     I
                       SPARKING
                       OR
                       SLOUGHING
                                                                                                     SPARKING

                                                                                                     SLOUGHING

U)

Ul
                                                                                                               7.8- 17 um PARTICLES
kj
'JUul il 1 11 1 Li 1 1 i lllJil
I
J J.I i l | i 1 II IkJl Lull 1 1 1 | I^IV HI 1,
I 1
j 	 oJlL-dlLL
i^l l^ i li Ju iJ,U i , L H kl It 1...
1 1 L
                                                                                                                3.8 - 7.6 um PARTICLES
           28001
                                                                                                                1.8- 3.6 Jim PARTICLES
                 Jw~*A*~K-**«--^»*-*^^                                                ^^^J^jui^^^j^^

                                                                                                                0.67 - 1.t um PARTICLES
                                                 Figure  11.   Chart recordings from the large particle sampling system.

-------
1011

1010
number'/DN m3
%
Q
O
0
•J
^
" 108


107
1C
I .
4 • ' I • T ' I • '
"i ~JL ,
~ 1 ^ 5
i f " :
'

« £
— o
§3
5 <
S UJ
O • NO RAP
& A RAP
— 5-
, 1 , . 1 . 1
-2 10'1 10° 10
           GEOMETRIC MEAN DIAMETER,
12.   The size distribution of the effluent from a precipitator
     installed on a pulverized-coal fed boiler.  Measurements
     were taken with and without rapping.
                      352

-------
2
CL
     10
     io"H
        -2.
                                         ±90.0
                                         -•99.0
                                                 u
                                                  _
                                                 b
             A
      f
                                        -•99.9
               I1
           OPEN SYMBOLS - NO RAP
           CLOSED SYMBOLS - RAP

               &AULTRAFINE
               O9IMPACTOR
         10
           ,-2
i  i i IIIHI   i  i MIHI|—i i  i mn| 99.99
      10
                      -i
10P
101
     PARTICLE DIAMETER  (MICROMETERS)
    Figure 13.  Fractional efficiency of an electrostatic precipitator
            showing the negative effects of rapping reentrainment.
                        353

-------
     Figure 10 shows data obtained with the sample  extraction-
dilution system and the optical and diffusional  sizing  systems
in the effluent stream from an asphalt batching  process.   The
need for size resolution in real time is clearly illustrated
as the two size fractions fluctuate in concentration, sometimes
in phase and sometimes out of phase.

     Figure 11 shows particle size and concentration recordings
from the large particle sampling system.  Emissions are  shown
in real time for 5 discrete size ranges.  From these data,  it
was possible to identify and analyze the contribution of  the
rapping puffs to the total emissions.

     In Figure 12, the size distribution measured at the  outlet
of a precipitator installed on the effluent stream  from  a coal-
fired boiler is shown.  Measurements were made with cascade im-
pactors and an electrical aerosol analyzer, with and without
rapping.  Rapping emissions can be seen to constitute a  large
part of the total emissions in the size range from  1 to  10  ym
diameter.

     Data of the type illustrated in Figure 12 are  taken  at pre-
cipitator inlets and outlets to determine the collection  effi-
ciency versus particle diameter (fractional efficiency).   The
collection efficiency of one precipitator is shown  in Figure
13.  The classical dip in efficiency near 0.5 ym is clearly
shown.  Also, the increase in penetration from rapping reentrain-
ment is seen to be quite large in the 1 to 10 ym size range.

     Particle sizing measurements are a valuable tool in  control
device evaluations, and yield necessary data for diagnoses  of
poor performance, model development, and for design purposes.
Efforts are continuing to refine the techniques  in order  to im-
prove accuracy and to reduce their complexity and cost.
REFERENCES

 1.  Marple, V.A.  The Aerodynamic Size Calibration of Optical
     Particle Counters By Inertial Impactors.  Part. Tech. Lab.
     Publication 306, University of Minnesota, 1976.

 2.  McCain, J.D., K.M. Gushing, and W.B. Smith.  Methods for
     Determining Particulate Mass and Size Properties:  Labora-
     tory and Field Measurements.  J. Air Pollut. Contr. Assoc.
     24(12):1172-1176, 1974.

 3.  Smith,  W.B., K.M. Gushing, and J.D. McCain.  Procedures
     Manual for Electrostatic Precipitator Evaluation.  EPA-600/7-
     77-059, U.S. Environmental Protection Agency, Research
     Triangle Park, NC, 1977.


                               354

-------
                              PAPER 17
            SOME STUDIES OF CHEMICAL SPECIES IN FLY ASH


                             L.D.  HULETT
                              J.F.  EMERY
                              J.M.  DALE
                           A.J.  WEINBERGER
                              H.W.  DUNN
                             C.  FELDMAN
                              E.  RICCI
                  ANALYTICAL CHEMISTRY DIVISION
                  OAK RIDGE  NATIONAL LABORATORY

                                AND

                           J.0.  THOMSON
                  THE UNIVERSITY OF TENNESSEE
ABSTRACT
     Fly ash  specimens  from  coal  fired  steam  plant precipitators
and sluice ponds  have been studied.   In precipitation ashes from
two different plants the  distributions  of  trace  elements  in the
matrix materials  that make up  the  ashes have  been found to be
the same.  Alkali,  alkaline  earths,  and rare  earths  are more
concentrated  in the mullite  phase;  transition metals such as
V, Mn, Cr, Co, and  Mo are more concentrated in the magnetic
phase; carbon and sulfur  are enriched in a cinder-type phase.
Ash samples extracted from sluice  ponds had brown iron-rich
phases that were  highly concentrated in As and Mo and enriched
in other elements.  The brown  phase  was not found in the  precipi-
tator ash, so we  speculate that a  transformation of  the ash has
occurred in the pond.   Some  initial  results of a glow discharge
spectroscopy  technique  for arsenic speciation are reported.
Mossbauer spectroscopy  has been used to determine iron chemical
states in both the  precipitator ash  and the pond ash.  Engineer-
ing studies of a  fly ash  treatment process that  would generate
iron compounds to scavenge and fix trace elements in sluice ponds
are recommended.
                               355

-------
INTRODUCTION

     Because of increased dependence on coal as a source  of
energy the disposal of ash from its burning presents an  increas-
ingly difficult problem.   The amount of fly ash generated in
the United States is estimated to be in excess of 4 x  10   tonnes
per year.  One can visualize a quantity such as this as  a pile
one meter high, covering  an area approximately 4% km square.
Many schemes for the disposal of this material are under  study.
A primary concern is whether or not trace elements such  as arsenic,
lead, and many others will be leached from the ash and contami-
nate the environment.  The detection of the trace elements, both
in the ash and its effluent, and the determination of  their con-
centrations is rather easily done, but the determining of their
chemical species  (valence, compound form) is not worked  out at
all.  A knowledge of the chemical species of elements  in  fly
ash  is considered very important in order to predict toxicities
and  the manner in which they will react with the environment.
For  example, it is believed that arsenic in the +3 state  is much
more toxic than that in the +5 form.  The determination  of va-
lences and compound forms of trace elements in fly ash is the
subject of this study.  The results and conclusions that  we will
present should be considered rather tentative.  Our study is
less than one year old and our ash samples have been taken from
only two TVA steam plants, Bull Run and Kingston, in the  immediate
vicinity of Oak Ridge National Laboratory.

     The chemist  has made some rather impressive accomplishments
in molecular spectroscopies capable of determining chemical
species:  infrared, ultraviolet, x-ray photoelectron spectroscopy
 (XPS), x-ray diffraction, and many others.  All of these  are
available to our  efforts, but in very few cases are sensitivities
sufficiently high to be able to determine chemical states directly
in fly ash.  XPS, for example, is capable of determining  valence
states, but it is a surface method, and surface concentrations
must be  in excess of 0.1 monolayer for most elements to  be de-
tected.  Most of  the trace elements in fly ash are more  dilute
than this.  There is no "magic spectroscopy" to which  we  can
expose fly ash and determine chemical states without disturbing
the  specimen.  This leads to the necessity of performing  chemical
and  physical separations on fly ash, which immediately opens
up the criticism  that the system is being disturbed and  probably
altered.  We argue that with present analytical capabilities
there is no alternative to this.

     Fly ash is a complicated mixture composed mostly  of  alumi-
num, silicon,  iron, titanium, alkali and alkaline earths, and
oxygen.  These elements are present in the form of both  amorphous
glasses and crystallized minerals.  The authors suspect  that
when the chemical species problem of trace elements is eventually
solved it will be found that the "chemical state" of a trace
element will be defined by the matrix in which it is dissolved.
We do not think  that  it  is likely, for example, that lead will
occur in an isolated pure form of PbO or Pb02 or  that  Cu will

                               356

-------
be found as CuSO^.   It  is  for  these reasons that we are direct-
ing a lot of our  efforts toward  studying matrix types.   We are
attempting to determine if certain trace elements are preferen-
tially associated with  certain matrices.

EXPERIMENTAL PROCEDURES

     Ash specimens  from two TVA  steam plants,  Bull Run  and Kings-
ton, located near Oak Ridge National Laboratory, have been col-
lected for study.   Both of these plants use the tangential firing
method which requires that the coal be pulverized to a  fine
particle size.  The pulverizing  step effects the removal of a
large percentage  of the sulfur-containing pyrites.   The flue
gas from the furnaces is passed  through cyclone and electrostatic
precipitators.  The ash that is  produced is sluiced to  ponds.
Specimens from  the  cyclones and  precipitators  of both of these
plants have been  collected.  No  attempt to collect  the  submicron
material that escapes from the stack has been  made  at this point.
Some specimens  from the uppermost strata of the Bull Run plant
sluice pond have  also been collected.

     Mossbauer  spectroscopy measurements were  made  by means  of
a specially designed spectrometer located at the University  of
Tennessee Physics Department.  Another specially adapted analytical
instrument is the glow  discharge spectrometer  developed by Feld-
man.1  This method  involves the  excitation of  the optical  spectrum
of arsine  (AsH3)  under  very low  background conditions.   Arsenic
in solutions as low as  0.1 ppb can be  detected.   By adjusting
the pH of the solution  being analyzed,  one can cause arsine  to
be evolved from arsenic in the As"1"3  state only or from  both  the
As+3 and As+5 forms.  At pH less than  1.5,  both the +3  and +5
states are reduced  to arsine.  At pH above 5, only the As+3  form
is reduced.  We thus have  a method of  differentiation between
As"1"3 and As"1"5.

     We have adapted a  special oxalate extraction method for
removing iron,  and  those elements associated with it, from the
work of Williams, et al.2   It  appears  that this will allow us
a method of speciating  arsenic on fly  ash surfaces.   Arsenic
is displaced from the fly  ash  surfaces into solutions by the
oxalate extraction. The solutions are then analyzed by glow
discharge spectroscopy. Oxalate does  not appear to interfere
with the method,  but one must  use deaerated solutions to prevent
oxidation of the  arsenic.

     Most of the  quantitative  elemental analyses performed on
the specimens of  this study were done  by neutron activation
analyses, but .x-ray fluorescence analysis was  also  used for  many
qualitative and semiquantitative measurements.  Carbon  and sulfur
analyses were done  by means of the Leco analyzer.

EXPERIMENTAL RESULTS

     When we examine the Bull  Run and  Kingston cyclone  and pre-
cipitator ashes by  the  optical microscope and  test their magnetic

                               357

-------
properties we are able to distinguish at  least  three  types of
matrices.  Their gray colors are due to white transparent  and
translucent particles interspersed with black magnetic  and non-
magnetic particles.  We have separated some of  the  black particles
from the white ones by individual "particle picking"  and by
magnetic extraction.

     X-ray diffraction patterns of the white phase  indicated
that quite a bit of material had mineralized into a crystal struc-
ture of the mullite type.  Mullite is a ceramic having  a highly
variable composition  (3 Al203-2 Si02-2 Al20?'Si02).   Its dif-
fraction pattern closely resembles sillimanite: Al203*SiO2.
Mullite exists in the glass as well as the crystalline  form.
In our specimens most of the white matrix material  is probably
glass, but the crystalline mullite is quite prominent.  Through-
out this paper we will refer to both the glass  and  crystalline
forms of the white matrix material as the "mullite" phase.  X-
ray diffraction patterns of the non-magnetic black  particles
also indicate a mullite structure, but in addition, there  is
an intense, broad-lined background due to elemental carbon in
a very finely divided state.  Diffraction patterns  of the  mag-
netic phase show it to have a well-known spinel structure  which
is usually assigned to Fe30,,.

     Mossbauer spectra were taken of the white matrix and  mag-
netic material.  For  the white material the spectra suggest that
iron in both the Fe+z and Fe*3 forms is present; two  sets  of
broadened quadrupole-split doublets were found, one narrow doublet
characteristic of Fe+3 and one with larger splitting  similar
to what is found for  Fe+2, but with a smaller isomer  shift than
usual.  The peaks corresponding to the magnetic phase were ana-
lyzed in terms of two six-line hyperfine splittings with fields
characteristic of magnetite, as would be expected for the  spinel
structure of this phase.  There is a slight departure,  however,
of our spectra from that of high purity magnetite.  Figure 1
is a Mossbauer spectrum of some as-received fly ash,  showing
peaks of both the magnetic and non-magnetic phases.   Those peaks
corresponding to the  magnetic phase are labeled FejO^ and  those
of the non-magnetic are labeled Fe+2 and Fe+3.

     Table 1 shows that trace elements in the alkali, alkaline
earths, and rare earths are higher in concentration in  the mul-
lite phase than in the magnetite phase.  These  data are averages-
of three measurements on different size fractions from  a Kingston
plant sample.  Table  2 shows an identical trend for these  ele-
ments for a Bull Run  fly ash sample.  The level of  concentrations
for the trace elements in the Bull Run sample is lower  than for
Kingston.  The elements V, Mn, Cr, Co, Mo and U appear  to  be
enriched in the magnetic phase, but only  by a factor  of 2.  Table
3 shows the composition of the black cinder phase  for both the
Kingston and Bull Run plants.  This phase is unique in  its en-
hanced concentrations of both carbon and  sulfur.


                               358

-------
o
1
V)
oc
 0.00  10.00  20.00  30.00  40.00  50.00  60.00   70.00  80.00  90.00 100.00 110.00 120.00

                                       CHANNELS

               Figure 1. Mossbauer spectrum of Allen Steam Plant fly ash.
                                          359

-------
TABLE 1.  DISTRIBUTION OF ELEMENTS IN MULLITE AND MAGNETIC PHASES
      OF KINGSTON  STEAM PLANT  FLY  ASH,  CONCENTRATIONS IN PPM


Element
Al
C
K
Mg
Ti
Ca
Na
S
Ba
Sr
Ce
La
Nd
Sc
Th
Sm
Dy
Cs
Hf
Eu
Lu

Element
Fe
V
Mn
Cr
Preferential Distribution in Mullite
Mullite Matrix
153,000
50,000
24,800
13,300
9,240
9,300
2,073
1,900
1,236
1,050
173
100
89
36
26
18
14
10
7
3
3
Preferential Distribution in Magnetic
Mullite Matrix
3,200
295
179
148
Matrix
Magnetic Matrix
64,000
4,800
4,200
6,000
3,586
4,600
355
1,500
425
443
68
33
0
17
12
10
8
4
3
1
2
Matrix
Magnetic Matrix
430,000
445
473
439
                                       (continued)
                               360

-------
TABLE 1 (continued)

Preferential
Element
Co
MO
U
Distribution in Magnetic Matrix
Mullite Matrix
45
0
15
(continued)
Magnetic Matrix
115
23
22
Random Distribution
Element
Rb
Ga
As
Se
W
Ta
Mullite Matrix
196
67
214
18
7
2
Magnetic Matrix
175
62
283
17
0
2
          361

-------
TABLE 2.  DISTRIBUTION OF ELEMENTS IN MULLITE AND MAGNETIC
          PHASES OF  BULL  RUN  STEAM PLANT FLY ASH,
                  CONCENTRATIONS  IN  PPM


Element
Al
K
Mg
Ti
Ca
Na
Ba
Sr
Ce
La
Nd
Sc
Th
Sm
Dy
Cs
Hf
Eu
Lu

Element
Fe
V
Mn
Cr
Preferential Distribution in Mullite
Mullite Matrix
155,000
20,100
11,800
9,475
2,500
1,225
515
360
150
84
32
30
24
15
10
10
6
3
2
Preferential Distribution in Magnetic
Mullite Matrix
17,600
206
82
170
Matrix
Magnetic Matrix
62,700
5,100
5,300
3,300
1,900
370
260
142
63
33
0
18
11
8
6
2
2
2
1
Matrix
Magnetic Matrix
465,000
304
270
260
                                     (continued)
                           362

-------
TABLE 2 (continued)

Preferential
Element
Co
Mo
U
Distribution in Magnetic Matrix
Mullite Matrix
28
0
9
(continued)
Magnetic Matrix
230
100
13
Random Distribution
Element
Rb
Ga
As
Se
W
Ta
Mullite Matrix
160
27
25
16
3
2
Magnetic Matrix
160
31
47
15
7
2
          363

-------
TABLE 3.  CONCENTRATION OF ELEMENTS IN CINDER MATRIX OF KINGSTON
         AND BULL RUN STEAM PLANTS, CONCENTRATIONS IN PPM

Element
C
Al
K
S
Mg
Ti
Ca
Na
Ba
Sr
Ce
La
Nd
Sc
Th
Sm
Dy
Cs
Hf
Eu
Lu
Fe
V
Mn
Cr
Co
Mo
U
Rb
Kingston Plant
450,000
78,*00
7,833
3,000
5,800
4,466
7,3f'Q
753
426
433
33
52
41
15
17
10
7
3
4
2
1
9,223
92
48
1£5
11
->
6
iS>
Bull Run Plant
241,200
60,200
5,550
4,150
3,880
3,510
1,050
378
155
250
65
35
0
13
10
7
5
4
3
2
1
6,850
90
24
180
13
7
4
75
                                     (continued)

                               364

-------
TABLE 3 (continued)

Element
Ga
As
Se
W
Ta
Kingston Plant
10
64
12
3
3
Bull Run Plant
6
20
35
2
1

     Samples were collected  from  the Bull Run sluice pond by
careful core drilling of  the  surface so as not to disturb the
stratification.  A  specimen  six centimeters deep was extracted
and divided into four strata.  The uppermost stratum was tan
in color.  The  tan  color  was  less for the second stratum.  The
lower two strata were slate  gray.  The data in Table 4 show quite
clearly why the color changed from tan to gray; the iron concen-
tration decreased with  depth  of the strata.  Note that the alumi-
num concentration,  and  some  other elements common to mullite,
increased slightly  with depth.  Since these data were taken by
neutron activation  analysis,  we do not have a direct measure
of silicon content.  There  is a remarkable regularity in the
manner in which certain trace elements change in concentration
as a function of stratum  depth.   As, Se, Br, Mo, Sb, Ba, Ga,
W, and Mn decreased uniformly with depth, while Sc, Cs, La, and
Nd increased slightly.

     Oxalate extractions  were done on the stratified samples
of Table 4.  Most of the  iron was removed, leaving the residues
qray in color.  Essentially  all of the arsenic and molybdenum
were removed from the specimens by the iron extraction Process.
Figure 2 shows  x-ray fluorescence spectra of the oxalate extract
and the residue of  the  uppermost  stratum.  The arsenic and molyb-
denum peaks of  the  residue  are not measurable, but in the dried
oxalate extract they are  quite prominent.


                                              w.
                      "
tofor BuS Run  sample, because of the higher  property of
magnetic phase.
                                365

-------
TABLE 4.  DISTRIBUTION OF ELEMENTS IN STRATIFIED SLUICE POND
        ASH.  BULL  RUN  PLANT,  CONCENTRATIONS  IN PPM

Element
Al
K
Mg
Ti
Ca
Na
Ba
Sr
Ce
La
Nd
Sc
Th
Sm
Dy
Cs
Hf
Eu
LU
Fe
V
Mn
Cr
Co
Mo
U
Rb
Ga
As
Se
W
Ta
Top Stratum
128fOOO
17,000
14,800
5,900
5,700
1,600
780
400
120
69
87
25
19
12
9
9
4
3
4
88,000
277
248
135
53
129
15
134
80
395
33
11
1
2nd Stratum
137,000
22,000
16,300
6,400
5,000
1.800
700
540
130
76
84
27
20
13
9
8
4
3
4
64,500
269
240
133
53
59
14
200
70
267
33
9
1
3rd Stratum
147,000
23,000
17,200
7,100
5,400
1,750
680
530
135
72
102
30
21
13
9
10
5
3
5
46,000
269
223
125
47
15
12
71
64
125
18
7
2
Bottom Stratum
157,000
23,000
17,500
7,500
3,500
1,300
350
217
140
74
123
32
23
13
9
10
5
3
5
17,500
248
104
125
44
12
10
220
46
30
11
8
2
                            366

-------
                                                                  FLY ASH
                                                                  AFTER
                                                                  LEACHING
                                                                  OXALATE
                                                                  LEACH
     Figure 2. Oxa/ate extraction studies of fly ash.  Lower spectrum: x-ray
              fluorescence spectrum of dried oxalate extract.  Upper spectrum:
              x-ray fluorescence spectrum of fly ash residue after extraction.
o
e/s
CA
                                                               Fe304
 0.00   10.00  20.00  30.00 40.00  50.00  60.00  70.00 80.00 90.00 100.00 110.00 120.00
                                     CHANNELS

          Figure 3. Mossbaucr spectrum of Allen Steam Plant fly ash after
                   oxalate extraction.
                                       367

-------
     Glow discharge spectroscopy measurements of oxalate  extracts
from Bull Run ash before and after it contacted the  sluice  pond
have been made.  The ratio of As+3/As+5 for  the precipitator
ash, before pond contact, was 0.020.  After  pond contact  (upper
stratum, Table 4) the ratio was 0.030.

     Another sluice pond specimen, very rich in the  brown iron-
containing component, was acquired.  Using  sedimentation  tech-
niques, the finely divided brown component  was concentrated into
a fraction relatively free of the coarser,  gray material.   X-
ray fluorescence showed again that this iron-rich  component had
high concentrations of As and Mo.  This component  was  examined
by Mossbauer spectroscopy at room temperature and  liquid  nitrogen
temperature.  No appreciable change  in the  spectrum  at the  lower
temperature was  observed, indicating that  the material was  prob-
ably not  a simple hydrated ferric oxide.   Hydrated ferric oxide
becomes magnetic at liquid nitrogen  temperatures and exhibits
multiplet splitting in  its Mossbauer spectrum.

     We suspect  that  the iron-rich component in the  sluice  pond
is  produced by a transformation of the fly  ash, possibly  the
oxidation of Fe30,,.   We have separated some ash into a magnetic
and a  non-magnetic component and subjected  both to aeration in
a water extract  of fly  ash in the laboratory.  The pH  of  the
water  extract  is 4-5.  After about five weeks of aeration,  the
solution  exposed to Fe30i, is acquiring a slight tan  color.   The
solution  exposed to the non-magnetic material is still colorless.

SUMMARY AND CONCLUSIONS

     Our  thesis  that  we stated  in the introduction of  this  paper,
that "chemical species" of trace elements  in fly ash might  be
determined by  the matrices that contain them, is given a  great
deal of support  by our  data.  There  does appear to be  a preference
for  the mullite  matrix  over Fe304 for the  trace elements  Ba,
Sr, Ce, La, Nd,  Sc, Th, Sm, Dy, Cs,  Hf, Eu,  and Lu.  It is  true
that the  magnetic phase also has appreciable concentrations of
these  elements,  but is  is not completely free of mullite,  and
we  think  that  this might actually be the carrier of  the trace
elements  instead of the Fe30,, matrix.  Table 1 shows that there
is  quite  a bit of aluminum in the magnetic  fraction  which we
assume is associated  with mullite.   The data in Table  2 are from.
a totally different steam plant, but they  are remarably similar
to  those  of Table 1.  This suggests  that there may be  a common
pattern in the way trace elements speciate  themselves  in  fly
ash matrices.  Perhaps  solubilities  play a  role.   The  above trace
elements  are members  of the alkali,  alkaline earth,  and rare
earth  families.  Since  these are soluble in glasses  it is not
surprising that  they  concentrate in  the mullite matrix.

     Since the mullite  phase is by far the  largest component
of  fly ash, it is obviously very important  to determine more


                               368

-------
specifics about  how trace elements are contained in it.  Linton
Evans, Williams,  and Natusch3  have shown that many of them occur
in the outer  surface layers of the particles.  This should be
explored further.   Also,  studies should be done on how trace
elements are  distributed  between the amorphous and crystalline
portions of mullite.  These are now in progress in our labora-
tory.

     Transition  elements  such as V, Cr, Mn, Co, Ni, Cu, and Mo
are  known to  be  soluble in iron oxides and many are capable of
forming  solid solutions in F^O,,.  The mixed spinel, NiFe20^,
for  example,  is  also magnetic and has an x-ray diffraction pattern
very similar  to  FejO,,. This led us to speculate that some of the
transition  elements may seek the magnetite matrix in preference
to the mullite.   The data for V, Cr, Mn, Co, and Mo support this
(our analyses for Cu and  Ni are not complete) , but the enrich-
ments are only by a factor of 2.  It appears that the transition
elements do favor the magnetite matrix,  but they are not  exclu-
sively associated with it.  The fact that the Mossbauer spectrum
of the magnetic  phase departs slightly from that of pure  Fe304
suggests that solid solutions may have occurred.

     The cinder  phase that we isolated was very rich in carbon
and  sulfur.   Perhaps the  sulfur was adsorbed on the surfaces
of the carbon; our x-ray  diffraction patterns showed that it
was  finely  divided.  In past work, we have shown that sulfur
is associated with fly ash surfaces.1*  We could find no clear
cut  evidence  of  other trace elements being preferentially concen-
trated in the cinder phase.  At the Asheville meeting,  where
this paper  was presented  orally, we stated that the cinder  phase
appeared to be rich in Se and Br; but since that time,  we have
examined other cinder specimens and found Se and Br to be much
lower.

     Fly ash  researchers  may have a lucky break with regard to
arsenic  speciation.  Previous work by ourselves1* and others show
that arsenic  is  primarily associated with fly ash surfaces.
Treatment of  fly ash with oxalate appears to elute a large por-
tion of  the arsenic.  Feldman's glow discharge spectroscopy
method is capable of distinguishing As+3 and As  .  Another
ORNL group  is also using  the glow discharge spectroscopy  method
to speciate arsenic in runoff waters from ash disposal sites.
The  ratio of  As+3/As+s was found to be slightly greater for ash
from precipitators than for ponded ash,  but this does not appear
significant to us.  Since the ratio in both cases is rather small,
we tentatively conclude that most of the arsenic is oxidized
to +5 before  it  contacts  the pond.

     We  think that in sluice ponds fly ash can undergo trans-
formations  such  that a new iron-rich phase is generated.   Arsenic
and  molybdenum can be translocated to this phase.  The color
of the Bull Run  pond ash  samples was considerably different from


                               369

-------
that of the precipitator specimens.  The upper strata of  the  pond
samples were deep tan because of high iron concentrations,  and
there was a definite correlation of the concentrations of As,
Mo, and other trace elements with iron concentrations.  The fact
that As and Mo ate removed simultaneously with iron, when it
is extracted with oxalate, suggests strongly that  they are  located
on the surface of the iron-rich phase.  There is a correlation
of other elements, Se, Br, Sb, Ba, Ga, W, and Mn with iron  con-
centration in the stratified pond samples, but we  have not  yet
shown a definite association with iron, as for As  and Mo.   Theis
has also reported correlations of certain trace elements with
both iron and manganese.5

     More work should be done to determine the exact nature of
the iron-rich material formed in sluice ponds.  Our Mossbauer
data show that is is not "hydrated iron oxides."  Also, engineer-
ing studies should bo considered for the processing of fly  ash
to promote the formation of iron compounds that are efficient
in fixing trace elements in sluice ponds and disposal sites.
Rather than allow the magnetite and other oxidizable iron com-
pounds to lie "useless in the pond, perhaps it would be practical
to transform them into trace element scavengers.

ACKNOWLEDGEMENT

     The authors would like to express their sincere apprecia-
tion to the Electric Power Research Institute, Palo Alto, Cali-
fornia, for the funding of this work.  We are especially indebted
to Dr. Ralph Perhac of that Institute for directing our attention
to the importance of fly ash chemical speciation.  Professor
Roger Minear of the University of Tennessee Chemistry Department
has also contributed to our overview of the fly ash problem.
Dr. Perhac and Dr. Minear have worked together to  facilitate
contacts between many individual researchers.

REFERENCES

1.   Feldman, C.  Annual Progress Reports, 1975, 76, 77, Analyt-
     ical Chemistry Division, Oak Ridge National Laboratory,
     ORNL 5100, ORNL 5244, ORNL 5360.  Improvements in the  Arsine
     Accumulation-Helium Glow Detector Procedure for Determining
     Traces of Arsenic, submitted to Analytical Chemistry.

2.   Williams, J.D.H., J.K. £yersr S.S. Shukla, R.F. Harris,
     and D.E. Armstrong.  Environ. Sci. Technol. 5(11) :113-
     1120, 1971.

3.   Linton, R.W., Peter Williams, C.A. Evans, and D.F.S. Natusch.
     Determination of the Surface Predominance of  Toxic Elements
     in Airborne Particles by Ion Microprobe Mass  Spectrometry
     and Auger Electron Spectroscopy.  Anal. Chem. 49:1514, 1977.
                               370

-------
4.   Hulett, L.D.,  T.A.  Carlson,  B.R.  Fish, J.L.  Durham.   Studies
     of Sulfur Compounds Adsorbed on Smoke Particles and  Other
     Solids by Photoelectron Spectroscopy.  In:  Determination
     of Air Quality,  G.  Mamantov  and W.D.  Shults, eds.  Plenum
     Press, New  York,  1972;  L.D.  Hulett, H.W.  Dunn,  J.M.  Dale,
     J.F. Emery,  W.S.  Lyon,  P.S.  Murty.   The Characterization
     of Solid Specimens  from Environmental Pollution Studies
     Using Electron,  X-ray and Nuclear Physics Methods.   Mea-
     surement Detection  and  Control of Environmental Pollutants,
     International  Atomic Energy  Agency Conference (IAEA  SM-206/1)
     Vienna, Austria,  1976.

5.   Theis, Thomas  L., and J.L. Wirth.  Sorptive  Behavior of
     Trace Metals on Fly Ash in Aqueous Systems.   Environ.  Sci.
     Technol.  11(12):1096-1100, 1977.
                                 371

-------
                             SUMMARY


          ADVANCES IN PARTICLE SAMPLING AND  MEASUREMENT
                         WILLIAM FARTHING
                    SOUTHERN RESEARCH  INSTITUTE

     The technology for particulate sampling in process streams
has been expanded and improved over the last several years.
New instruments have been developed, traditional devices and
methods have been refined, and standard procedures have been
established.  The Process Measurement Branch of the Environmental
Protection Agency's Industrial Environmental Research Laboratory
sponsored a symposium in Asheville, NC, on recent developments
and related research.

     The symposium began with papers concerning inertial effects
of sampling and sizing by inertia.  C.N. Davies reviewed theo-
retical and experimental work concerning the aspiration coef-
ficient of sampling tubes and presented some new findings.  His
primary emphasis was on the inability of the existing theory
to account for all of the effects of a finite wind velocity on
the aspiration of particles with finite inertia by a sampling
tube with finite diameter.  An experimental test of one expres-
sion, a quadratic equation of the Stokes number, was presented
for tubes sucking at right angles to the wind.  The comparison
showed that the level of aspiration predicted by the quadratic
was too high and there was evidence that at least a cubic equa-
tion is necessary.  A potentially useful criterion was also given
for accurate sampling at low wind speeds relative to the sampling
velocity.

     In a paper presented by Koichi linoya, the observed and
calculated effects of anisokinetic sampling were presented for
round and slit probes.  It was suggested that the results pre-
sented could be used to estimate sampling errors.  The concen-
tration errors were smaller at extremely high sampling velocities,
so super high speed sampling could be a simple method without
the tedium of isokinetic sampling.  The amount of particles de-
posited in the probe and sampling tube was found to be minimized
when the Reynolds number was between 2000 and 3000.  In a  study
                               372

-------
 of the effect of probe diameter on  sampling  errors with  isokine-
 tic sampling, it was found that the reproducibility, measured
 in terms of the standard deviation  of  the  deduced concentration
 from many tries, of sampling experiments decreases as the probe
 diameter decreases.  In those experiments  the average deduced
 concentration increased as the probe diameter decreased.

      Other  work described by Dr. linoya concerned particle impac-
 tion efficiencies on ribbons suspended at different orientations
 across a pipe and impactors with different clearance ratios,
 defined as  the ratio of the nozzle  to plate distance over the
 nozzle diameter.  In the ribbon study, calculations based upon
 a  discontinuous potential flow model agreed well with observed
 efficiencies over a wide range of particle Reynolds numbers
 extending from the Stokes to Newton regions.   (These  velocities
 are somewhat higher than employed in typical impactors for sam-
 pling process streams.)  The purpose of the work concerning
 impactors was to theoretically account for the effects of the
 velocity boundary layer at the nozzle outlet of  impactors using
 a  potential flow model.  Good agreement with measured efficiencies
 was claimed at ratios of 2, 1, 0.5,  0.33,  and 0.25.

      The performance of cyclone collectors and samplers  was de-
 scribed by  Morton Lippmann.  Traditionally used  for control de-
 vices,  cyclones are now being routinely used  for sampling of
 "respirable" aerosols for assessment of health effects.   More
 recently, cyclones have been introduced for in-situ classifi-
 cation of aerosol size distribution.  Cyclones have been  designed
 with sharp  collection efficiency versus size  curves comparable
 to impactors down to particle diameters of  0.5 ym while  offering
 several advantages such as no deterioration in performance with
 large samples and much simpler operation than with  dichotomous
 samplers.  The major problem is the  lack of an accurate  theory
 to be used  for design purposes.   One important point  of  this
 paper was the evidence that caution  must be exercised in  coupling
 cyclones in series because it may affect flow and thus  the be-
 havior.   An empirical relation for  efficiency was presented in
 this paper  with four constants.   The constants have been  evaluated
 for  eleven  cyclones for which reliable  calibrations exist cover-
 ing  a range of particle sizes from 0.3  to  10  ym  and gas  flow
 rates from  0.1 to 2700 Jl/min.

      Recently developed systems for  particle  sizing by  impactors
 were described by Michael Pilat.   The University of Washington
 Mark 4  Cascade Impactor utilizes low absolute gas pressure re-
 sulting  in  large Cunningham correction  factors permitting in-
 ertial  sizing of particles from 0.02 to 0.2 ym in diameter.
 In  conjunction with the University of Washington Mark 3  Impactor,
 two  systems,  one with 0.5 acfm and another  with  1.8 acfm flow
 rate,  have  been assembled and tested which  size  particles from
 0  02  to  20  urn.   A new impactor for  high concentrations,  using
many  stages (28)  to reduce overloading, has also been constructed
 for  sizing  particles from 0.05 to 30 ym.
                                373

-------
     Recent work with the Sinclair diffusion battery was described
by Earl Knutson.  It has been coupled to a data processing  sys-
tem which enabled unattended runs of several days with hourly
sampling.  The penetration of particles through the battery was
measured with a new continuous flow condensation nuclei counter.
Experience has revealed several improvements in operating proce-
dures.  An iterative mathematical technique was studied and
chosen to calculate size distributions from the data obtained.
Nearly 1000 size spectra of New York City urban aerosol have
been analyzed showing typical geometric mean diameters from 0.025
to 0.050 ym with geometric standard deviations from 1.8 to  2.0.

     Although in-situ sizing of particles is available, many
instances still arise when laboratory sizing is desirable.   Ronald
Draftz described the instruments available for such work.   Such
measurements can be very sophisticated and can include shape
measurements in short times.  The electronic image analyzers
are extending the practicality of the many useful measurements
possible with a light microscope.  The problem of particle  ag-
glomeration remains unsolved.

     A recent field evaluation  (at a Canadian lead smelter)  of
five real time particulate monitors, all commercially available,
was described by A.W. Gnyp.  Two transmissometers, a mass monitor
based on the backscattering of light, a charge transfer monitor,
and a beta radiation attenuation device were rated according
to accuracy, reliability, and maintenance over a one year period.
Accuracy was based upon the proportionality of the instrument
signal to aerosol mass concentration determined as a reference
by a manual sampling train.  The sensitivity of the monitor out-
put to particle size distribution and composition was evaluated
using impactors and laboratory analysis of samples as references.
The overall conclusion was that reliable continuous mass monitor-
ing is now possible in stacks if the aerosol physical and chemi-
cal properties are approximately constant, as found in process
streams  that have passed through efficient control equipment.

     A real time in-situ particle sizing probe utilizing small
angle light scattering is being developed under the sponsorship
of the Process Measurement Branch of USEPA/IERL.  The field
prototype of the instrument exhibited at the symposium is now
being tested.  Robert Knollenberg described the operation prin-
ciple and some preliminary results from a coal-fired power  plant.
The instrument covers a 0.3 to 10.0 ym size range with 60 chan-
nels resolution.  The major uncertainty in sizing spherical par-
ticles with the instrument, performed by relating size to flux
scattered at small forward angles by single particles, is the
particle refractive index giving at most an error of ±20% and
normally within ±10% of actual size.  The concentration range
for accurate measurements limited by coincidence counting in
the present model is 5 x 10"/cm3.  Normally, the main effect
                               374

-------
of  higher concentrations is to decrease  the effective size ranqe
An  optical velocimeter is also designed  into the  instrument.
The present design permits temperatures  up to 250°C and veloc-
ities  up to 30 m/sec.  The results of an initial  in-stack test
at  a coal-fired power plant with an electrostatic precipitator
and a  scrubber were reasonable.  Calculated opacity from the
measured particle size distribution was about 15% while measured
opacity  was 17%.  The calculated mass loading was 0.01 to 0.02
g/m with a volume average diameter of about 1.3 Mm.   It appears
that the instrument was capable of resolving several  size modes
in  this  test.

     Another in-situ portable light scattering instrument being
developed under EPA sponsorship to determine size distribution
was described  by A.L. Wertheimer.  This device measures  flux
scattered from many particles simultaneously at three  small
angles relative to the forward direction, 4°,  8°,  and  11°,  and at
a range  of large angles of 80°-100°.   Each measurement is per-
formed at two  wavelengths, 0.45 and 0.9 urn,  and the large angle
scattering is  measured at two orthogonal polarizations.   The
instrument relates the small angle signals dominated by  Fraun-
hofer  diffraction to the volume of particles  in three  size ranges,
centered at 1.0, 3.5, and 7.0 ym.  For the lower  end of  the size
distribution,  the difference in the two 90°  signals at two
orthogonal polarizations obtained with the 0.9  urn  (0.45  pm) wave-
length is related to the volume of particles  in a  size range
centered about 0.4 ym (0.2 ym) .  The  size range, mass  loading,
and temperature range are 0.1 to 10 ym,  4 to  400 ppb by  volume,
and 0° to 260°C.  The prototype had just been  delivered  to EPA
to  be  tested in a wind tunnel facility.

     Kenneth T. Hood reported the results of  studies performed
by  the National Council for Air and Stream Improvement concerning
the relationships of plume opacity, in-stack  opacity,  and contin-
uous mass monitors to mass emission rate as  defined by filter
samples.   A previous study had indicated the  validity  of an  in-
stack  transmissometer to monitor particulate  concentrations  in
flue gas,  and  calibration curves had  been obtained for each  site
to  provide mass concentrations from transmissometer opacities.
In  these studies observer opacity was frequently related to par-
ticulate concentration through use of simultaneous transmissom-
eter measurements and their calibration curves.   The opacity
studies  involved five different sites: a lime  kiln, two  kraft
recovery furnaces (one with a direct  contact  evaporator, and
one without) ,  and two wood and fossil fuel-fired boilers (one
with coal  and  another with oil) .  The observer  opacity under
good contrast  conditions (dark or blue sky background)  was found
to  vary  between ±10 and ±15% opacity  from the average.  The  rela-
tionships  of plume opacity to in-stack opacity were generally
found  to be linear;  however,  the slopes were  not one as  might
be  expected and varied from site to site, and the  curves did
not  intercept  the origin.   At the non-direct  contact evaporator
system,  75%, 50%,  and 25% of the technically  trained observers

                                375

-------
read a non-visible plume at instrument opacity levels  of  6%,
8%, and 10%, respectively.  In tests of the mass monitor  based
upon backscattering of light,  it was compared to transmissometer
behavior at two kraft recovery furnaces and a wood-waste  fired
spreader stoker boiler.   The mass monitor was found to be equi-
valent to the transmissometer in quality of data and perform-
ance except that the former required less attention at high load-
ings (3.76 g/acm)  at which the latter required frequent cleaning.

     After three sessions on instruments for sampling and measur-
ing aerosols, the topics of the meeting turned toward procedures
for using the data and quality control.  A computer based data
reduction system for cascade impactors, developed under EPA
sponsorship, was described by Joseph D- McCain.  The system of
programs, becoming available for general use, utilizes calibra-
tion information for each impactor with operating conditions,
time, and stage weights to determine particle size distributions
in any one of several forms for individual runs or averages there-
of.  The first program in the series utilizes a spline technique,
described as an "automated French curve", to fit a curve to the
cumulative size distribution.  If differential mass or differen-
tial number size distributions are desired, these are obtained
from the cumulative curves which are forced to be continuous
in coordinates and slopes.  Statistical analyses, including the
location of outliers, are performed on the data.  Additional
programs permit data sets from inlet and outlet measurements
of control devices to be combined to determine fractional ef-
ficiencies.  The program in its present form handles all com-
mercially available round jet cascade impactors, including common
modifications, which are in current use in stack sampling.  Other
round jet and slot type impactors could be accommodated with
slight program revision.

     In the area of instrument calibration, D.Y.H. Pui described
various aerosol generators now available.  Three instruments
provide monodisperse aerosols for primary standards over a broad
range of sizes:  the vibrating orifice aerosol generator for
diameters of 0.5 - 50 ym, the mobility classifier monodisperse
aerosol generator for diameters of 0.01 - 0.5 ym, and the ultra-
fine condensation monodisperse aerosol generator for smaller
sizes.  The constant output atomizer aerosol generator provides
polydisperse aerosols of high concentration and stability.  In
addition, some calibration measurements of various aerosol measur-
ing and sampling devices were reviewed, and comparative studies
showed good agreement between different types of instruments.

     Quality control work by EPA was presented by D. Bruce Harris
and Gene Tatsch.  Particle bounce or blow off is perhaps  the
major problem associated with particle sizing with cascade im-
pactors.  The use of substrates on collection plates such as
grease or glass fiber filter material has been employed to reduce
bounce.  Tests were performed to ascertain which of the available
substrates are most suitable for flue gas sampling.  Of nineteen

                               376

-------
greases  tested,  only Apiezon H grease was found to perform satis-
factorily  at  temperatures above 149°C (300°F).  At higher tem-
peratures  glass  fiber material appeared to be more stable.  How-
ever, large mass changes, induced by reactions related to SO*
concentrations,  were observed with glass fiber and to a lesser
extent with grease.   After various laboratory and field tests
a treatment procedure for glass fiber was identified which signi-
ficantly reduces mass gains.  This treatment involves washing
the substrates in I^SO,, followed by rinsing, drying, baking
and in-situ conditioning before use in impactors.   Reeve Angel
934AH glass fiber filter material performed best among those
tested.  It was  pointed out, however, that filter  materials
change from batch to batch.   The details of the results of this
study are  available  in a recent report.

     In  another  area of quality control, Mr.  Tatsch described
problems which have  arisen because different  procedures are  pres-
ently utilized to reduce and present data,  specifically that
from impactors.   Methods are being sought to  alleviate such
problems.  It is hoped that  the computer programs  described  in
the paper  by  Mr. McCain will be a practical means  for uniform
data reduction and presentation with the required  versatility.

     The last session of the symposium contained three papers
concerning the procedures by which the available technology  is
utilized to evaluate particulate control devices:   scrubbers,
baghouses, and electrostatic precipitators.   The first paper,
by Richard Chmielewski, was  concerned with  identification  and
solutions  of  problems which  arise in sizing wet particles.   It
was suspected that because of the pressure  reduction  from  stage
to stage,  evaporation of water  from particles occurred inside
cascade  impactors.  This was indicated by  disagreement between
measured size distributions  and those predicted from  scrubber
theory.  Laboratory  experiments with a University  of  Washington
cascade  impactor and a series of glass impactors verified  this
suspicion.  The  jet  diameter of the glass  impactors could  be
adjusted to minimize pressure drop.   It  was also found that  pres-
sure drop  across a stage is  higher for wet  particles  than  dry
ones.  Based  on  the  laboratory  results a single stage impactor
usable in  the field  with a variable cut  point was  constructed
using a  Greenburg-Smith impinger to minimize  pressure reduction
and evaporation  time.   In one application  the measurements agreed
with the prediction  that the condensed particle  size  distribution
should have a minimum aerodynamic diameter  on the  order of 0.5
urn.  Also  discussed  were problems which  arise in measurements
of'entrainment where particles  above 10  urn are  involved.   None
of the attempted techniques	hot wire anemometer, cascade im-
pactor,  and chemical stain methods—give  completely  satisfactory
results.
                                377

-------
     A presentation of the measurements necessary  for  evaluation
of fabric filter control devices by D.S. Ensor stressed  the  im-
portance of a systems approach and real time monitors  for  a
meaningful evaluation.  The overall mass loading is normally
very low and cleaning processes cause large fluctuations  in
loading	at some units one compartment per minute receives  a
burst of air in the reverse direction.  This is accompanied  by
large changes in the velocity distribution of the  stream.  Other
aspects causing variations are bag integrity, bag  conditioning
time, and valve malfunctions.  The problems of matching  data
sets obtained at different locations with different instruments
are reduced with a mobile control room containing  an automatic
data logging system with a common time base.  Sizing instruments
utilized in evaluations are diffusion batteries, optical particle
counters, electrical mobility analyzers, and cascade impactors.
In addition, gas monitors, pressure transducers, and a light
scattering nephelometer are used to track the dynamic  behavior
of both the baghouse and the source.

     The presentation concerning electrostatic precipitators
by Wallace B. Smith also stressed the importance of monitoring
transient events.  Rapping reentrainment of short  duration has
been found in many installations to be responsible for most  of
the total emissions.  If, for diagnostic purposes, collection
efficiency due  to electrostatic behavior is sought, the measure-
ment program must differentiate between the different  types  of
emissions:  simple penetration, rapping reentrainment, sneakage
around the collection fields, and boil up from the hoppers.
A measurement system was described which determines collection
efficiency for  particles from 0.01 to 10 ym diameter.  It  in-
cludes cascade  impactors, mass trains, electrical mobility ana-
lyzers, diffusion batteries, and optical particle  counters.
A specially designed extraction-dilution apparatus is  used to
condition the aerosol for compatibility with the latter  three
instruments.  Laboratory experiments were performed to determine
the effects of  particle charge upon impactor behavior.  The
experiments showed that, at high charge levels, size distribu-
tions determined with impactors are significantly  skewed toward
larger sizes.   However, at charge levels produced  in electro-
static precipitators on process streams (where fields of 4 -
8 x 103 V/cm are employed), the effect of particle charge was
not significant.
                               378

-------
     Research  into  the chemical state of fly ash was the last
topic on the program.   L.D.  Hulett reported some results from
a program  to develop methods for trace element analyses in fly
ash and in waters with which it has been in contact.  The samples
studied came from a precipitator hopper and a sluice pond dis-
posal site at  a  coal-fired power plant.  The analytical procedures
discussed  were x-ray fluorescence, scanning electron microscopy,
optical microscopy, x-ray diffraction, x-ray photoelectron spec-
troscopy,  Mossbauer spectroscopy, flow discharge spectroscopy,
and chemical separation.  None of these techniques can discrim-
inate chemical states of trace elements from fly ash matrix,
so the  indirect  approach of oxalate leaching was utilized.  This
treatment  separated iron in the +2 and +3 valence states accom-
panied  by  nearly all of the arsenic and molybdenum present  espe-
cially  after exposure to the pond.  It appears that these were
associated with  the iron on the fly ash surfaces.  Most of  the
lead was  found in  a phase, termed "mullite", consisting mainly
of ferroaluminosilicate glass.  Selenium was concentrated in
a black cinder phase consisting of a combination of carbon  and
"mullite".   A  phase, termed "magnetite", was identified as  rela-
tively  free  of trace elements.  A method was developed  using
glow discharge spectroscopy to determine the ratio As+3/As+s
in water  exposed to fly ash.  Other trace elements observed on
the surfaces were  zinc, copper, selenium, and bromine.   A search
for the valence  states of other elements will be continued.
                                379

-------
                    METRIC CONVERSION FACTORS
To convert from;

 Ib
 gr/ft3
 ft3/min (cfm)
 lbs/in.2
 °F
 ft2/1000 cfm
 in. WG
 gallons
 ft
 in.
 tons
 in.3
 ft3
 gal/min
 ft2
 in.2
 gal/1000 ft3
 grams
 ft/min
 ounces
 oz/yd2
 grains
 gr/ft2
 Ib force
 lb/ft2
 in. H20/ft/min
 Btu
 To;


kg ,
g/m3
m /sec
kg/m2
°C
m2/(m3/sec)
mm Hg
liters
m
m

kgs
cm
m3
I/sec
m2
cm2
1/m3
grains
cm/sec
grams
g/m2
grams
g/m2
dynes
g/cm2
cm H20/cm/sec
calories
Multiply by;

   0.454
   2.29
   0.000472
   703.
   (°F-32)  x 5/9
   0.197
   1.868
   3.785
   0.3048
   0.0254
   908.
   16.39
   0.028
   0.0631
   0.0929
   6.452
   0.135
   15.43
   0.508
   28.34
   33.89
   0.0647
   0.698
   44.44 x  105
   0.488
   5.00
   252
                              380

-------
                                TECHNICAL REPORT DATA
                          (flease read Instructions on the reverse before completing)
1. REPORT NO.
 EPA-600/7-79-065
            3. RECIPIENT'S ACCESSION- NO.
4. T,TLE AND SUBTITLE proceedings:  Advances in Particle
Sampling and Measurement (Asheville, NC, May 1978)
            5. REPORT DATE
            February 1979
                                                      6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
                                                      8. PERFORMING ORGANIZATION REPORT NO.
W.B.  Smith, Compiler
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Southern Research Institute
2000 Ninth Avenue, South
Birmingham, Alabama 35205
            10. PROGRAM ELEMENT NO.
            INE623
            11. CONTRACT/GRANT NO.
            68-02-2131, Task 21306
12. SPONSORING AGENCY NAME AND ADDRESS
 EPA, Office of Research and Development
 Industrial Environmental Research Laboratory
 Research Triangle Park, NC 27711
            13. TYPE OF REPORT AND PERIOD COVERED
            Proceedings; 1/77 - 9/78
            14. SPONSORING AGENCY CODE
             EPA/600/13
 15. SUPPLEMENTARY NOTES IERL-RTP project officer is D. Bruce Harris,  MD-62,  919/541-
 2557.
 16. ABSTRACT rj,ne proceedings consist of 17 papers on improved instruments and tech-
 niques for sampling and measuring particulate emissions and aerosols; e. g. , cas-
 cade impactors, cyclone collectors, and diffusion-battery/nuclei-counter combina-
 tions.  Transmissometers and instruments for measuring scattered light were used
 for continuous monitoring of emissions from a secondary lead smelter and from
 three pulp and paper mill sources (a wood-waste-fired power boiler, a kraft reco-
 very furnace, and a lime kiln). Also discussed were: computer-based data reduction
 for plotting curves of particle size distribution; equipment for generating aerosols
 and its use in calibrating instruments; analysis for trace elements in fly ash; and
 sources of sampling errors. Applications of improved techniques for evaluating
 emission control devices included: a wet impingement technique for  measuring par-
 ticle sizes in wet scrubbers; use of  real-time instruments in studying the dynamic
 behavior of baghouses; and measurement of fractional collection efficiency and
 detection of fly ash entrapment in electrostatic precipitators.
17.
                             KEY WORDS AND DOCUMENT ANALYSIS
                 DESCRIPTORS
                                          b.lDENTIFIERS/OPEN ENDED TERMS
                                                                    cos AT I Field/Group
 Pollution             Diffusion
 Dust                 Transmissometers
 Aerosols             Light Scattering
 Sampling             Lead
 Measuring Instruments  Smelters
 Impactors            Paper Industry
 Cyclone Separate
ia. "DISTRIBUTION STATEMENT

 Unlimited
Pollution Control
Stationary Sources
Particulate
Cascade Impactors
Nuclei Counters
Lime Kilns
Baghouses
19. SECURITY CLASS (ThisReport)
Unclassified
13B
11G
07D
14B

131
07A
20N,20F
   07B
   11F
   11L
                        21. NO. OF PAGES
     390
20 SECURITY CLASS (Thispage)
Unclassified
                        22. PRICE
EPA Form 2220-1 (9-73)
                                           381

-------