EPA-650/2-74-014
October 1973
Environmental  Protection Technology Series
                                                                   m
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                     V
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                                EPA-650/2-74-014
    DEVELOPMENT  OF  A
LOW PRESSURE IMPACTOR
                  by

 A. R. McFarland, H. S. Nye, and C. H. Erickson

            Anderson 2000 Inc.
             P. O. Box 20769
          Atlanta, Georgia  30320
          Contract No. 68-02-0563
         Program Element No. 1A1010


      EPA Project Officer:  R. K. Stevens

      Chemistry and Physics Laboratory
     National Environmental Research Center
   Research Triangle Park , North Carolina 27711
              Prepared for

    OFFICE OF RESEARCH AND DEVELOPMENT
   U.S. ENVIRONMENTAL PROTECTION AGENCY
         WASHINGTON, D.C. 20460

              October 1973

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                        EPA REVIEW NOTICE

This report has been reviewed by the National Environmental Research
Center - Research Triangle Park, Office of Research and Development,
EPA, and approved for publication.  Approval does not signify that the
contents necessarily reflect the views and policies of the Environmental
Protection Agency, nor does mention of trade names or commercial
products constitute endorsement or recommendation for use.
This document is available to the public for sale through the National
Technical Information Service, Springfield, Virginia 22161.
                                  11

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                            ABSTRACT







        A Low Pressure Impactor aerosol sampler  was designed





fabricated and tested.  The  system injests  a fixed aerosol flow rate





of 1  cfm at inlet conditions and causes  the particulate  matter to be





separated and collected on four atmospheric pressure and three





reduced pressure impaction stages and an after-filter.  Cutpoint





sizes of the stages are 9. 7,  5.0, 2. 46,  1.21,  0.355, 0.141,  and 0. 05





micrometers for spherical particles  with a density of  2 gm/cm3.





Each of the impaction stages is fitted with a glass fiber media





collection substrate to facilitate gravimetric  analysis  of the collected





samples.





        Experiments conducted with laboratory aerosols  show the





system to have  wall losses less  than  6  percent when the  mass median





diameter of the aerosol is 0.6 micrometers.   For particles 6. 1 microns





in size,  the wall losses on the upper  stages are less than  11  percent.





Both particle rebound and re-entrainment from  the collection surfaces





are shown to be negligible.  Each low pressure  stage can be loaded





with more than  10 mg of deposited  aerosol without re-entrainment





occurring.
                            ill

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                TABLE OF CONTENTS







               Title                        Page Number






INTRODUCTION                                  1





INERTIAL IMPACTOR PERFORMANCE             9




LOW PRESSURE IMPACTOR DESIGN             16





EXPERIMENTAL PROGRAM                     20




FIELD TESTS                                  37





SUMMARY AND CONCLUSIONS                   43





REFERENCES                                  46
                         IV

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                LIST OF ILLUSTRATIONS


Figure                   Title                    Page Number

   1          Impactor Stage-Single Jet Type             3

   2          Low Pressure Impactor Unit                6

   3          Low Pressure Impactor System             7

   4          Collection Characteristics of              10
             Multi-Jet Inertial Impactor
             for ReS 100
             Effect of Jet Reynolds Number             15
             upon KQ

             Apparatus Employed  in Aerosol            21
             Tests
             Size Distributions- Typical Test            23
             Aerosols

             Size Calibration of Low Pressure          25
             Impactor

             Particle Bounce Characteristics of        33
             Stage LP-3 (0. 05/^m Cutpoint)
  10         Loading Curve for Stage LP-3             36
             (0. 05 j/m Cutpoint)  of Low Pressure
             Impactor

  11         Size Distribution of Cigarette Smoke       38

  12         Size Distribution of Atmospheric           40
             Aerosol June 30-July 20, 1973 at
             Urbana, Illinois

  13         Size Distribution of Atmospheric           41
             Aerosol July 21 -August  15, 1973
             at" Urbana,  Illinois
                          V

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                    LIST OF TABLES
Table                Title               Page Number
          Low Pressure Impactor            19
          Design and Operational
          Parameters-1 cfm Inlet
          Flow Rate
          -24. 3 mm Hg Pressure
          in Expansion Chamber

          Wall Losses  for Individual          Z9
          Impactor Components

          Wall Loss Characteristics          31
          of Original Stages "A" and
          "B"
                           Vl

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                         LIST OF SYMBOLS


 A      =   1.23,  a constant

 C      =   Cunningham's Correction

 D-      =   Jet Diameter

 D      =   Particle Diameter

 D      =   Particle Diameter for which Stage Efficiency is 50
            percent

 K      =   Inertial Parameter

 K 5    =   Value  of Inertial Parameter for which Stage  Efficiency
            is 50 percent

 KT     =   Value  of Inortial Parameter Corresponding to Conditions
            Employed  in a Particular Test

 L      =   Distance from Jet Exit Plane to Collection Plate

 P      =   Air Pressure at Jet Exit Plane

 Q      -   0. 41,  a constant

 Re-     -   Jet Reynolds  Number

 T      =   Air Temperature at Jet Exit Plane

 VQ     =   Air Velocity at Jet  Exit Plane

 b       =   0.44,  a constant

77       =   Stage Efficiency

r/       -   Value  of Efficiency Obtained Experimentally

X       =   Mean Free Path of  Air Molecules

 M-       =   Dynamic Viscosity  of Air

p       =   Density of Particulate Matter
 P
                        vii

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                      INTRODUCTION








Background





        The deleterious effects  of atmospheric particulate matter are





numerous  and varied.  These include:





        Reduction of solar radiation (which causes a decrease  in





        seasonal temperatures) Landberg1 reported that urban





        areas receive up  to 20% less insolation than rural areas.





        Robinson2  and Holzworth3 demonstrated that there is a





        relationship between visibility and the amount of particulate





        matter in the atmosphere.





        Corrosion of metals Hudson4 observed that industrial





        locations with high concentrations of particles and oxides





        of sulfur are more corrosive  to steel and zinc than less





        industrialized ares.





        Interference with photosynthesis  Particles settling on





        vegetation interfere with light required for photosyn-





        thesis thereby lowering starch production by the plant





        (Czaja5 and Bohne6).





        Human health hazard  Atmospheric particles are suspect





        as  being a threat  to human health' since these may be





        intrinsically toxic,  may carry an adsorbed toxic material





        or  may  interfere  with the clearance mechanisms in the





        in  the respiratory tract.

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       In all of the  above areas the knowledge of the size of the par-


ticle is vital to understanding its effects and determining the best


methods to control particulate emissions from man made sources.


       In the case of examining the role of aerosols as public health

                                           Q
hazards,  the Task Group on Lung Dynamics  noted the utility of a


sampler which can be used to determine the size of particles in aero-


dynamic terms.   The degree of penetration and retention of particles


in the respiratory system is  a function of aerodynamic   size'.


Particles are,  to a large extent selectively deposited by aerodynamic


size in the nasopharyngeal,  tracheobronchial,  and pulmonary areas


of the respiratory system.  Final deposition site also depends on


variations in the respiratory air flowrate, and on physiological


considerations.


       The use of aerodynamic sizing is of interest not only because


it allows simulation of  the important size parameter in lung deposition


but also because it renders itself to the measurement of the  aerosol


mass-size distribution.  Although there are various types of apparatus


which could be used  to acquire size distribution data based upon


aerodynamic size, the  most widely used are cascade impactors.


With reference to Figure 1 the cascade impactor draws an aerosol


sample  through a series  of two or more stages made up  of a jet or


orifice plate and a collection surface.  As the  air flows through the


jet it is accelerated to  a  specific velocity and directed towards the

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GAS
STREAMLINE
                k\\\\\\\\\\\\\\\T\\\\\\\\\ >
                    COLLECTION
                    PLATE
                                            -JET
.TRAJECTORY OF A
"HIGH  INERTIA PARTICLE
                                             TRAJECTORY OF A

                                             LOW INERTIA PARTICLE
      FIGURE I  - IMPACTOR  STAGE - SINGLE JET  TYPE

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collection surface  and through the following jet stage.  Particles  with





sufficient inertia cross the air flow stream lines and impact on the





collection surface.  The smaller particles, which have insufficient





inertia,  follow the stream lines into the next impactor  stage.  By





employing several stages in series  it is possible to separate  an





aerosol into size groupings.   Samplers which characterize atmos-





pheric particles  in this manner have been available since  1945 when





May10 developed a four stage cascade-type inertial impactor.





       May's first impactor  employed rectangular jets, however,





Ranz and Wong11 found better efficiency characteristics and sharper





cuts could be obtained with round jet impactors.  In 1958,  A. A.  Ander-





sen12 developed  a cascade inertial impactor for bacterial  sampling





which employed  multiple jets  on each stage.  Subsequently developed





versions of the apparatus have found application in atmospheric and





stack sampling.





       Inertial impactors commonly used up to the present time





have had the capability of sizing particles to a lower limit of  approxi-





mately 0.4 micrometers.  This operational characteristic has





limited the study of the submicron components of aerosols such as





motor vehicle exhaust (which  at cruising speeds consists of particles





of carbon, motor oil,  aldehydes, ketones  and lead) approximately





70 percent of which have an equivalent size for unit density particles





of less than 2 microns.13  Indeed,  ninety  percent of the lead  by

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weight is  associated with particles of sizes less than 0.5 micrometers.14





Other important submicron  aerosols include, stationary source combus-





tion products,  photochemical aerosols, oil mists and metallic fumes.





       The limitation on particle  size can be extended to much smaller





diameters if the impactor is operated  at a reduced pressure.  Basic





investigations by Stern and Zeller15 demonstrated the feasibility of





such an approach.   Subsequently,  McFarland and Zeller16 conducted





in-depth studies to determine  the  operational characteristics of a low





pressure  impactor and, recently,  Bucholz^ '  conducted  tests with an





impactor  operating  at reduced pressure for separating particles of





0. 1 micrometers and  smaller.





Purpose of Study





       Although the feasibility of  particle  collection by low pressure





impaction has been  demonstrated, the concept has not been extensively





used in air sampling.   The reason is principally due to the lack of





specially  designed apparatus.





       The purpose of the present study was  to design, construct and





test a prototype cascade impactor which can be used to determine  the





mass-size distribution of  atmospheric  aerosols as small as  0. 05





micrometers for a density of 2 gm/crn3.   The basic design of the





resulting  device,  which is shown schematically in Figure 2 and photo-





graphically in Figure  3, incorporates  the configuration of a conventional




Andersen non-viable impactor* in four stages of a high pressure section
#Andersen-2000 Inc.   Atlanta, Georgia

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                               INLET
          INLET PORT
        STAGE  A
        STAGE  B-
        STAGE  C-
        STAGE  D
        BASE
  THROTTLIN
  NOZZLES


   EXPANSION
   CHAMBER
u_
i
CE
UJ
               DETAIL   A
        PRESSURE
        TAP
                  — RUBBER GASKET
                    TEFLON GASKET
                    GLASS FIBER PAPER
                    TEFLON GASKET
                    JET PLATE
                    RUBBER GASKET
                                                      /EE  DETAIL  A


                                                     AFTER- FILTER
PRESSURE  TAP
                                                  ---SUPPORT BASE

                                                       OUTLET
        FIGURE 2  -LOW  PRESSURE  IMPACTOR UNIT

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war  PRESSURE
GAGE
LOW  PRESSURE
iMPACTOR
                             COURSE
                             CONTROL
                             VALVE
    FINE  CONTROL
    VALVE
FIGURE  3- LOW PRESSURE IMPACTOR  SYSTEM

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                                                                    8
(to separate  particles larger than 1. 21 ^m) followed by three stages





in the low pressure section which effect separation of particles down





to 0.05 micrometers.  The first four stages operate at atmospheric





pressure and the low pressure stages  operate at approximately 1/30





atmosphere.





        The unit has been laboratory tested to determine efficiency





characteristics and to evaluate the performance limiting character-





istics of (1) the loss of particles to internal surfaces other than the





collection plate (wall losses), (2) the particle rebound  or bounce





characteristics for the stage -which has the highest air velocity,





and (3)  the mass loading capability of the low pressure stage which





should be most susceptible to re-entrainment of a deposited sample.

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              INERTIAL IMPACTOR PERFORMANCE





        The size selection characteristics of an inertial impactor



stage are reflected by the efficiency with which the  stage collects



variously sized particles.  In turn,  the efficiency, which is commonly



called the impaction efficiency,  77 ,  is a function of three dimension-



less parameters;
               rj  =  f(K,  L/Dj,  RSj)





       where;



               K  =  Inertial Parameter



            L/D. .=  Aspect Ratio



             Re-  =  Jet Reynolds Number
                J




Of these dimensionless groups,  K  has the most significant influence



upon  r\ - - the other two may  be considered to be second order



variables .



       R?nz and Wong11 carried out studies with impactors which



had single  circular or slit jets on each stage and related the  collections



efficiency to the inertial parameter.   Later an experimental  investi-



gation by McFarland and Zeller ! s showed the relationship between



K  and 77 for a stage with  multiple circular jets.  A typical curve



relating  these two variables  is shown in Figure 4.

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LU
O
o:
UJ
   00
   80
O
z
UJ  60

O

LL_
U_
LU
   40
                                                     10
a
o
o
    0
            O.I     0.2     0.3     0.4

        INERTIAL  PARAMETER  , K , DIMENSIONLESS
   FIGURE  4 - COLLECTION  CHARACTERISTICS OF

              MULTI-JET  INERTIAL IMPACTOR

              FOR  Rej>IOO

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                                                                   11
In this work, the inertial parameter is defined as:

                     Cp  V D  2
               K  =    Pop
        •where;



               C   =  Cunningham's slip correction factor

               Q  -  particle density

               V  =  jet exit velocity

               D  =  particle diameter

                IJL =  air viscosity

               D. =  jet exit diameter



        It is customary to attempt to represent the r\ vs-   K curve by

a single value,  namely that of  the inertial parameter which corresponds

to 50 percent efficiency, K  ,-•   For a given stage operating with  fixed

values  of all variables involved in  K  other than particle  size, the

7] vs.   K curve can  also be represented by the diameter of a  spherical

particle which would be removed with 50 percent efficiency.   This

parameter is called  the stage cutpoint and  is denoted by D  (-•

        In the design of an inertial impactor stage it would appeal-

possible to achieve small values of  the stage cutpoint through either

increasing the jet velocity or  reducing the  jet size.  However, this

approach does have its limitations.   When  velocities much greater

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                                                                  12







than 3000-4000 cm/sec are used,  small particles may tend to either




rebound or become re-entrained from the collection surface.  In




addition,  it is  presently not practical to use jet diameters smaller




than approximately 0.01 inch.  As a consequence, the smallest




cutpoint which can be reliably achieved through varying  the jet




velocity and diameter is approximately 0. 5 micrometers.




        Closer observation of the impaction parameter reveals that




if the value of  Cunningham's correction,  C,  can be increased, it rnay




be possible to  achieve  a cutpoint diameter without resorting to high




jet velocities or extremely small  jet diameters.




        Cunningham's correction,  C, takes into account  the non-




continuum nature of gas flow about the particle.  The factor  C




increases  directly with the increase in the mean  free path length of




the  molecules  while increasing inversely with particle size.



                l R
        Milliken    has  shown  C  to accurately be represented by:
                        DP



              A   -   mean free path of gas molecules




                  -   0.0685 micrometers  at standard atmospheric


                     temperature  and pressure




               A  -   1.23




               Q  =   0.41




              .b   =   0.44

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                                                                  13
        For small values of  ^   , C ^ 1,  where as for large values
                            DP
of —— , C  ^ —- (A+Q).   For a perfect gas,  the mean free path X
     P           P
can be represented by:
               \  =  1.70 x 10"5T/P

               T  =  temperature,  °K

               P  =  pressure, mm Hg


It may be noted that  X is  inversely proportional to pressure.

Reference to the definition of the inertial parameter indicates that

a reduction in  pressure will  increase C thereby giving a larger

values for K   and  thus allowing for collection of smaller aerosols

with a given stage.

       The effect of  pressure upon C  may be  noted by the example

that the value is 1. 6  for a 0.3 micron particle  at atmospheric pres-

sure whereas  it is  23. 1  for the same particle at 1/30 atmosphere.

       While the influence of the aspect ratio,  L/D.,  and the jet

Reynolds  numbers, Re., are of second order importance,  they do

somewhat affect the collection efficiency of an impactor.  The air

jet  effluxing from the nozzle  remains relatively intact,  independent

of aspect  ratio, as it approaches the collection plate.  There is,

however,  a small change in streamline curvatures  as the aspect

ratio is varied and, as a consequence,  a variation in collection

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                                                                  14
efficiency.  For values of L/D- between 0. 55 and 5, Marple    shows





that the shift in K  c is less than 3  percent.





        Both the velocity profile  at the jet exit plane and the boundary





layer on the collection plate  are affected by the  jet Reynolds  number.





As  Re-  is decreased the value of K   increases.  McFarland and





Zeller,   in their  study with multiple-jet stages, made a linear





interpolation of experimental data  to show this effect.  A  plot of





their results,  adjusted to show  K g = 0. 14 for large values of the





Reynolds  number,  is  presented in  Figure 5.   In the design of an





inertial impactor,  it is possible to take into  account the shift in





K  5 caused by the  Reynolds number effect, thus a well defined D





exists for a given impactor stage operated under fixed conditions.

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                                                            15
 •Q  o.te
cc
UJ CO
1- en
< 2
o: o

o_ en
  z
2 UJ
    _,„
    O.fb
    0.14
    0.12
             20      40      60      80      100

       JET REYNOLDS  NUMBER, Rejf DIMENSIONLESS
        FIGURE  5 - EFFECT OF JET REYNOLDS NUMBER

                   UPON  K05

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                                                                  16



                LOW PRESSURE IMP AC TOR DESIGN



        The fundamental criteria employed in the development of the


Low Pressure Impactor were that the system should sample at a flow


rate of 1.0 cfm, that the outpoints of the first and last stages  should


be approximately 10 and 0.05 micrometers,  respectively,  and that


the collected samples should be compatible with gravimetric  analysis.


        The approach selected was to use a system which is divided


into two sections--  a set of four impactor stages •which operates at


atmospheric pressure and  a set of three impactor stages together


with an after-filter  which operates at reduced pressure (See Figure  2)


The two sections are separated by a throttling plate which serves  not


only to create  a pressure drop but also  limit the flow  through  the


system to  an equivalent of  1 cfm at  inlet conditions.  To minimize


aerosol losses from jets effluxing from the throttling  nozzles,  an


expansion  chamber  with an axial length  of over 1 ft. has been  employed.


        Basically, the upper four stages of the system are similar to


the Andersen non-viable sampler, however the unit has been  modified


to the  extent that the jets of the first two stages  are few in  number


(only 36 per stage) and have tapered inlets. Also,  the collection


plates  of these two stages are designed  to permit air to flow both

                                                   collection
around the edges and through one-inch holes in the/plate centers.


Collection in the upper stages is  effected upon 81 mm  diameter

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                                                                  17







substrates composed of glass fiber filter media.





        The principal elements in low pressure stages of the unit are





three jet plates, a collection plate, an after-filter support and gaskets.





The stages  are arranged  such that air is passed through the jet plate





of the first  stage and directed towards the second stage jet plate.





The holes in the two plates are offset to permit  the second  stage jet





plate to  serve  as the collection plate for the first stage.  Particles





are deposited on a special glass fiber filter media collection  substrate.





Proper values of the aspect ratio  are obtained through the use of a





neoprene gasket to separate the jet plates.   To preclude the glass





fiber media from adhering to either the gasket or the jet plate, thin





teflon gaskets  are placed  on either side of the media.





        The  air from the first stage impaction process is directed





through  the  jets of the second stage (which  are situated under opening





in the first  stage collection substrate) and the process is repeated.





For the  third stage,  impaction takes place upon  a surface designed to





serve only the purpose of  holding  a collection substrate.  After passing





the third stage, the air flows through a glass fiber filter  and  is dis-





charged from the system.





        The  system is setup such that the only variable  that need be





controlled during sampling is the  pressure level in the  expansion





chamber.  This value is measured with the aid of a percision Wallace





and Tiernangage and is to be maintained at 24. 3  mm of mercury.

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                                                                 18
       Stage outpoints for the system were calculated using the data





shown in Figures 4 and 5.  The resulting design specifications for





the system are presented in Table 1.   The four atmospheric pressure-





stages are denoted by A,  B, C and D whereas the low pressure stages





are listed as L/P-1,  LP-2 and LP-3.  Selection of cutpoints was set to





provide a ratio of approximately  two between successive stages in  the





high pressure section and a ratio of approximately three between





successive low pressure  stages.

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TABLE 1.   Low Pressure Impactor Design and Operational
            Parameters  - 1 cfm Inlet Flow Rate
                        - 24.3 mm Hg Pressure in Expansion Chamber
Number of
Stage Jets
A (Modified) 36
B (Modified) 36
C 400
D 400
LP-1 600
LP-2 600
LP-3 1762
Aspect
Diameter Ratio
(inches) L/D.
J
0.
0.
0.
0.
0.
0.
0.
161 0.55
104 0.9
0295 3
0187 5
0547 2.2
0398 3.0
0208 2.9
Jet
Velocity
cm/sec
100
240
269
668
1606
2886
4158
Jet Reynolds
Number
Re.
254
393
127
200
45.9
61.4
40. 5
Stage Outpoints
(Dp>5,m)
9.7
5.0
2.46
1.21
0.355
0. 141
0.050

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                                                                 20






                   EXPERIMENTAL PROGRAM







        A set of laboratory tests was conducted with the prototype





Low Pressure Impactor to verify the design stage  cutpoints and to




quantify the performance limiting factors of:  losses to internal





surfaces of the impactor other than the collection surface (wall





losses), particle bounce  and re-entrainment, and the mass loading




characteristics.  Basically, these tests involved subjecting the





sampler to an  aerosol which has known (or  easily measurable)




properties and which is  readily identifiable.  The aerosols were





generated with two types of apparatus:  a spinning disc atomizer





and a nebulizer, *" with  the first device serving the purpose of form-




ing large (> 1  micrometer diameter) particles and  the  latter  device




being used to  generate the  smaller aerosols.   For  both systems, the





aerosol generators formed a spray from a solution of 70 percent




uranine dye and 30 percent methylene blue dye dissolved on a solution




of 67 percent  ethyl alcohol and 33 percent water.  Evaporation of the





spray droplets produced  the actual test aerosol. Particle size was





varied by changing the concentration of the  dye solutions.




        The basic  layout of apparatus employed in the testing is shown





schematically  in Figure 6. Aerosol from either the  spinning disc or air




blast atomizer was passed through an 8-inch diameter duct.  One





sample stream of the aerosol  was drawn at a flow rate of 1 cfrn

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                      SPINNING  DISC
                      AEROSOL
      fAIR BLAST
       ATOMIZER
            1
                          W&T
                          PRESSURE
                          GAGE
                            A
                                                                 VACUUM
                                                                 PUMP
       MEMBRANE  FILTER HOLDER
LOW  PRESSURE
1MPACTOR
            MAIN CONTROL
            VALVE
                                                                    .VACUUM
                                                                    PUMP
\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\
            FIGURE 6 -APPARATUS EMPLOYED  IN  AEROSOL TESTS

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                                                                22
into the Low Pressure Impactor and a second sample stream, also at





a flow rate of 1 cfm, was drawn through a 47 mm glass fiber filter





mounted in a membrane filter holder.   The purpose of the latter





sample was to monitor the  constancy of aerosol output.





        For each test performed with the spinning disc generator,  a





sample of aerosol was collected on a membrane filter and a micro-





scopic size distribution  was made.  Figure 7 shows the results





obtained from such  a determination.  The  characteristic aerosol





size was represented  by a mass-average size which was obtained





by converting the microscopic data to a mass basis and calculating





the average value.





        The nebulizer  used  to generate  the submicron aerosols was





a Model 099 Dispos-A-Neb manufactured by Bio-Logics, Incorporated.





For determination of the particle sizes created with this device,





samples were collected  on  electron microscope grids using  a





Thermosystems, Incorporated electrostatic sampler.  These were





subsequently sized from photomicrographs taken with the aid of  a





Hitachi HU-11 transmission electron microscope.   Figure 7  shows





results obtained  from sizing a typical submicron aerosol.





Stage Outpoint Sizes





        To obtain the desired cutpoint of 0. 05 micrometers for the





final stage,  LP-3,  of the Low Pressure Impactor, it is necessary





that the pressure level at the jet discharge plane.be 22. 1 mm Hg.

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CL
Q

VI

CO
111
N

co
   98
   95-
   9O
   70
Q
UJ
5  50
o
CO
CO
CO 30
CO
>-
QQ
   10
UJ
o
cc
UJ
CL  5
                             AIR BLAST ATOMIZER

                             AEROSOL GENERATOR
                                                       SPINNING DISC

                                                       AEROSOL GENERATOR
   0.02         0.05      O.I                   0.5       1.0
                     PARTICLE DIAMETER , Dp, MICROMETERS

          FIGURE 7-SIZE  DISTRIBUTIONS-TYPICAL  TEST AEROSOLS
                                                                           5.0
                                                                                        UJ

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                                                                 24




Since the pressure level for the system is sensed  at the expansion



chamber and there are pressure losses as the air flows through



each impaction stage, it was necessary to determine pressure



variations in the low pressure system.  The results of such a check



show;





        LOCATION                           PRESSURE



Jet Exit Plane of Stage LP-3                 22. 1 mm Hg



Jet Exit Plane of Stage LP-2                 23. 6



Jet Exit Plane of Stage LP-1                 24. 2



Expansion Chamber                          24. 3





Design  cutpoints  for stages LP-1,  LP-2 and LP-3, which are shown



in Table 1,  are based upon these pressure levels.  The  predicted



cutpoints are also shown graphically in Figure 8 wherein the cutpoints



are presented not only for a particle density of 2 gm/cm3 but also



for 1 and 4 gm/cm3.   Operation of the impactor with the predicted



cutpoints is obtained  when the expansion chamber pressxire is set



at 24. 3  mm Hg.  Use  of lower pressure levels will shift the cutpoints



of the low pressure stages  to smaller values.



        In order to verify the design cutpoint particle sizes of the



low pressure stages,  detailed tests were  conducted with stage LP-3.



Since this stage has the smallest jets,  largest value of L/D., and



smallest value  of Re.  of the low pressure stages,  it is anticipated
                   J

-------
0.01
       ABC     D        LP-I     LP-2
              STAGE    NUMBER
    FIGURE 8-SIZE CALIBRATION OF LOW PRESSURE
LP-3
              IMPACTOR

-------
                                                                  26







that any deviations from design predictions would be most easily





observed by testing this  stage.





        The tests were conducted using the apparatus arrangement





shown in Figure 6 with the aerosol generated by the nebulizer.  The





high pressure stages  of the impactor were left in  place during these





tests in  order to strip the largest particles from the distribution.





The low pressure stages were re-arranged such that LP-3 was placed





above  LP-1  and LP-2.  During  operation,  aerosol was drawn through





the impactor system for a time sufficient to collect an easily measur-





able quantity of uranine dye.  The amount of uranine collected by





stage LP-3 and the  remaining components  of the low pressure section





of the  impactor was determined by washing the parts in distilled





deionized water to extract the uranine dye  and  subsequently analyzing





the wash water  with a Turner Model 110  Fluorometer. From the.





resulting data,  the test  efficiency -n  , of stage LP-3 was determined.





Next,  a  value of the inertial parameters,  KT,  which corresponds  to





the test  efficiency was taken from Figure 4 and the following equation





employed;
                           T

-------
                                                                 27






        This expression was solved for D   ,- based upon knowledge
                                        p. o



of the  size  and density of the test particles and upon an assumed




value of two for the density of the outpoint size particles.




        This method was chosen because the cutpoint size can be




determined from a minimal number of tests.   Reliance is placed




upon the impaction efficiency curve only to the extent that the slope




is utilized.




        The results for triplicate tests with stage LP-3 are shown




in Figure 8 superimposed upon the curve •which gives the predicted




cutpoint size for the  system.  It  should be noted the experimental




data verifies the calculated cutpoint of 0. 05 micrometers for the




last stage.




        Similar tests were  performed  on stages  C  and  D  of the




high pressure section using particles  produced by the spinning disc




aerosol generator.  In this case  the impaction stage to be tested




was placed  first in the impactor  and its efficiency determined.




Following the prodecure given above the values of D  ,- were computed.




These  results, which are also shown in Figure 8,  support the predicted




cufcpoint sizes.




Wall Losses




        Wall losses in cascade impactors can be attributed to the




following factor-s; high jet  and other internal velocities,  close




spacing of internal components and abrupt changes in air direction

-------
                                                                 28







at locations other than collection surfaces.  Use of an impactor with





any of these design deficiencies may result in a high ratio of internal





wall losses to sample collected.  The relatively large geometric





scale of the low pressure impactor together with the multi-jet





principle renders it a device which has inherently low wall losses.





        At the present time, the only method to reliably quantify wall





losses is through the use of controlled laboratory experiments.  The





approach used to acquire these data for the low pressure impactor





involved the following procedure.





        Prior  to the  onset of each test run,  the entire impactor was





washed with a laboratory grade detergent and rinsed with distilled,





deionized water.  The unit was then subjected to a heterogenous





uranine-methylene blue aerosol created by the nebulizer (geometric





standard deviation of approximately three).  At the completion of





each test run,  the individual collecting surfaces and the  internal wall





surfaces were again washed with a measured volume  of distilled,





deionized water to extract  the dye.   The wash water was then subjected





to fluoroscopic analysis to quantify the uranine mass  which has been





deposited on the impactor surfaces.





        The results obtained for aerosols with mean sizes  of 0.3





and 0.6 micrometer are shown in Table 2.  It may  be noted that





totally the losses  were less than 6 percent in each case.

-------
                                                                 29
               TABLE 2.   Wall Losses for Individual
                           Impactor Components
Impactor Components
Inlet

Jet Plate A (Modified)

Jet Plate B (Modified)

Jet Plate C

Jet Plate D

Interface

Throttling Plate

Expansion Chamber

Jet Plate LPI-1

Jet Plate LPI-2

Jet Plate LPI-3

All other extraneous
      surfaces

Total Wall Losses
Percent Wall Losses for given
       Aerosol Size
0. 3 micrometers
0.
0.
0.
0.
0.
0.
0.
1.
0.
0.
0.
1.
5.
053
160
193
226
206
034
866
545
499
293
149
307
43
0. 6 micrometers
0.
0.
0.
0.
0.
0.
0.
1.
1.
0.
0.

5.
031
170
230
190
230
015
860
530
990
460
090
058
85

-------
                                                                 30







       Early in the experimental testing phase of the program it





was  noted that stage A and  B  had inordinately high wall losses





(Table 3).   To reduce this phenomenon a design change was under-





taken.  For both stages A and  B  the number of jets was reduced





from 400 to 36 and, correspondingly the diameter  of the jets was





increased (to 0. 161 inches for stage  A  and 0. 104 inches for  stage





B).  In addition the intake sides  of jets were chamfered 60°.  A one





inch diameter circle was cut in  the center of the collection plates of





both stages   A and B  to  reduce the  volumetric flow rate (and hence





the velocity) of gas passing around  the periphery of the collection





plate.  These modifications  provided a drastic reduction in wall





losses when tested with a  monodisperse 6. 1 micrometers diameter





uranine aerosol (Table 4).





       Wall loss data for  the remaining upper stages, C  and  D,





were also acquired.  Here it may be  noted that the losses for each





stage are approximately 2 percent when the  stage is tested with





particles of size similar to the stage cutpoint size.





Particle Bounce





       Particle bounce  can greatly reduce the efficiency of an





inertial impactor.   If the collection surface  is a smooth plate, as





the jet velocities are increased  beyond 3200 cm/sec     in the





lower stages  of the impactor an increase in  particle bounce and





re-entrainment can be  expected. The problem may be partially

-------
                                                                 31
             TABLE 3.  Wall Loss Characteristics of
                          Original Stages "A" and "B"
Jet
Stages
A and B
A and B
Sampler Flow
Rate (cfm)
1. 3
1. 0
Test
Size
6
6
Aerosol
(fim)
. 1
. 3
Wall Losses
Percent
32
40
. 4
. 0
             TABLE 4.   Wall Loss Characteristics
                          of Upper LPI Stages ("A" & "B" Modified)
                          -Flow Rate - 1  cfm
  Jet
Stages
Test Aerosol
 Size ( p. m)
Wall Losses
  Pe rcent
A and B  (Modified)
  D
    6. 10

    3. 44

    1. 02
   10. 7

    2. 2

    2. 2

-------
                                                                 32







controlled by employing thin viscous coatings  on the collection





surfaces,  since the coating will both create a  condition  of inelastic





impact and at the same time provide an adhesive force to retain the





particles on the collection surface.   An alternate approach,  which





serves to increase adhesion, is to employ glass fiber  filters as the




collection substrates.  This method offers  a considerable advantage





over the use of viscous coatings in that less substrate preparation





is required and the substrates  render themselves better to  standard




analysis procedures.





        To determine if the glass fiber filters  used  in the low pressure




section of the system were effectively preventing rebound of impacted




particles, a set of tests was conducted with stage L.P-3.  This par-





ticular stage was chosen for detailed study because it has the highest





jet velocity, 4160 cm/sec.  In  conducting these  tests,  the stage was




operated in a manner in which  the velocity  could be varied yet the





predicted efficiency could be held constant.





        If particle bounce were a problem,  the expected result of





a plot  of efficiency vs.  velocity would show  a decrease in efficiency





with increasing velocity as the particle bounce phenomenon comes




into play.  The results of the tests,  which are presented in Figure 9,





show the efficiency of the stage increases  slightly with increasing





jet velocity (due  to a jet Reynolds number effect not adequately





compensated for in the test conditions).  The efficiency curve in the

-------
Ld
O
o:
UJ
CL
   100
 - 80
O

Z

UJ
h-

O
LU

_J

_J

O

O
   60
   40
20
                                   o

                                   3
                                   LU
                                   CD

                                   2
  ,0
UJ i


Sli

2 UJ
CO CD

W<
UJ H-
Q CO
                  2000           4000            6000           8000


                        JET  VELOCITY  , Vj ,  cm/sec



         FIGURE 9 - PARTICLE  BOUNCE  CHARACTERISTICS  OF STAGE LP-3
                    (0.05 fjm CUTPOINT)
                                                                             Co

                                                                             UJ

-------
                                                                 34






vicinity of the design velocity'did not drop which gives evidence that





particle bounce is not a significant problem with the low pressure




section of the impactor.





       With respect to the high pressure stages,  McGregor^   '





conducted bounce  tests with a standard Andersen non-viable sampler




and found that a stage with a cutpoint of 1. 1 micrometers (for unity





density particles) could be operated at a velocity five times as large





as the velocity encountered in stage  D  of the  present system with-




out a rebound phenomenon  being noticeable.  Based upon this result





it would be expected that the upper stages  of the present design would





not be subject to a limitation caused by particle bounce.




Loading Characteristics





       When substantial  quantities of aerosol are deposited on the





collection plate of a given stage,  it is possible that portions of the





collected  material could  be re-entrained by the air stream and be





subsequently re-deposited  on lower stages.  Under such circum-





stances,  misleading size distribution data would be obtained.





       The tendency of an  impactor stage  to be susceptible  to





re-entrainment problems can be tested experimentally by subjecting




the stage  to a known aerosol and studying the  relationship between




the mass  of material sampled and the collection efficiency.  Should





re-entrainment occur,  the efficiency would show an apparent drop





as the mass loading is  increased.   Tests of this type have been

-------
                                                                 35
conducted with a standard Andersen non-viable sampler by


           (20)
McGregor.       His results,  when applied to the upper stages



of the low pressure impactor  system, indicate that the permissible



mass loadings of Stage A woxild be approximately 2 mg, that of



Stage C would be about 13 mg and that of Stage D should be approxi-



mately 8  mg.  Loadings above these values do not show abrupt



re-entrainment effects, but rather a gradual decrease  in efficiency



of the stage.  In addition for the stages with  smaller cutpoints,  the



loadings limitation is more  pronounced as the jet diameter is



decreased and the velocity increased.  Since Stage  LP-3 has both



the highest velocity and the  smallest jet sizes of the low pressure



stages,  it was selected for an investigation of the loading charac-



teristics.  It was  assumed that  if  the loading limitations of stage



LP-3 were acceptable, so would be those of stages LP-1 and LP-2.



       The tests -were conducted by exposing  stage LP-3 for varying



times to a dye aerosol generated by the nebulizer.  After each run,



the efficiency of the stage as well as  the total quantity of uranine



aerosol collected  by the imp-actor  was determined for  each test.



The results,  shown in Figure  10 demonstrate that the  efficiency  of


      LP-3
stage/  is constant up to a sample load of over 10 mg,  indicating



that overloading is not a problem.

-------
  100
Ssok,	                       «                 ^
or    w             O
UJ
a.
O  60
z
UJ

O

u_
U_
UJ  40
o
^  20
O
o
      	|	|	_J	I   1114	|	|	1	|	|   111^

    0.2                0.5            1.0            2.0                 5.0            IQ.O

                              MASS LOADING , mg

         FIGURE  10 - LOADING CURVE FOR STAGE LP-3(0.05Mm OUTPOINT) OF LOW           w
                     PRESSURE  IMPACTOR                                                ^

-------
                                                                  37





                     FIELD  TESTS








        The Low Pressure Impaetor  system was setup to simultan-





eously  sample aerosol in parallel with a standard Andersen non-





viable unit.  For the first experiments the two devices were exposed





to a well-mixed  and diluted cigarette smoke.  The mass collected





on the various stages of both impactors was determined  through





measurement of the weight change of the glass fiber collection





substrates using a semi-micro analytical balance.  All collection





substrates were  conditioned for several hours  to the laboratory





environment before the weight measurements were  made.  The





resulting data, which has been converted to cumulative distributions,





is shown in Figure  11.  In this case  the particle size  parameter





represents  that of eqxiivalent spheres of unit density.   It may be





noted that there is good agreement between the  data obtained from





use of the two devices for  sizes larger than approximately 0.6





micrometers.   Below this size the Low Pressure Impaetor tends





to show a greater relative abundance of small particles.





        With respect to the mass of aerosol collected  by each unit,





the sum of all differential  •weights for the Low Pressure  Impaetor





was  78.9 mg whereas that of the standard non-viable  sampler was





79. 5 mg.





        Both units were exposed to atmospheric  aerosol for times





sufficient to collect several tens of milligrams  in each unit.   The

-------
o.
Q
VI

V)
LU
CO

X
Q
LU
I-
<
O
O
CO
CO
CO
CO
CD
LJ
O
(T
Ld
Q_
     96
95
     90
70
     50
     30
O   STANDARD ANDERSEN NON-VIABLE SAMPLER

A   LOW PRESSURE IMPACTOR (LPI)
                      PARTICLE DENSITY = I gm/cm3
10
                  0.05      O.I                   0.5        1.0
                         PARTICLE  DIAMETER, MICROMETERS ( jim)
                 FIGURE II- SIZE DISTRIBUTION OF CIGARETTE  SMOKE
                                                                         5.0
                                                                                   U)
                                                                                   00

-------
                                                                 39






purpose of collecting  these substantial quantities of mass was to





minimize any errors  associated with the process of measuring




differential weights of the substrates.  Results for two separate





atmospheric aerosol runs are represented in Figures 12 and 13.





In both runs  the Low Pressure Impactor yielded data which indicates




greater percentages of particles  of size less than 0. 6 micrometers.





Additionally,  the data presented in Figure  12 shows that the Low





Pressure Impactor collected substantially  greater fractions of the





very large particles.   Nineteen percent of the  aerosol mass was





associated with sizes  larger than 16 micrometers.  With reference




to Figure 13, it would appear that the Low Pressure  Impactor




collected less material of large sizes than did the standard non-





viable unit.  However, the cumulative distribution curve is misleading




for this test  since  it presents percentages  rather than actual mass




values.  The raw data showed nearly identical quantities of large





particles 'were collected  by the two devices (for example the total




mass of all particles larger than 7 micrometers  in size collected by




the Low Pressure  Impactor was 3. 79 mg whereas that of the standard





non-viable unit was 4. 13 mg).  But, the Low Pressure Impactor




System collected more total mass (41. 99 mg versus 31. 04 mg)





therefore the cumulative distribution of the Low Pressure Impactor




is shifted to the left.

-------
Q.
Q
VI

CO 90
UJ
N

CO
Q 70
LJ
h-
O
O
CO
CO
CO
CO
  30
m
LU

DC 10
LU
     O

     A
STANDARD  ANDERSEN NON -VIABLE  SAMPLER

LOW PRESSURE IMPACTOR (LPI)
                  ASSUMED PARTICLE DENSITY
                  = |grn/cm5
O.i
                             0.5       1.0                  5.0

                      PARTICLE  DIAMETER, Dp, MICROMETERS

          FIGURE 12 -SIZE DISTRIBUTION OF ATMOSPHERIC AEROSOL

                    JUNE 30 - JULY  20 , 1973 AT URBANA, ILLINOIS
                                                  10.0
20.0

-------
ex
Q

VI


-------
                                                                 42


       In addition to determinations of the aerosol  size distribution,

comparative values  of average aerosol concentrations were calcu-

lated.  These results,  presented in the following table, show that


                                Average  Concentrations
    Test              Std.  Non-Viable Unit   Low Pressure Impactor

June 30 - July 20         39.0 ^g/m3            86.2  ^g/m3

July 21 -  Aug. 15         30. 3                   42. 9



the Low Pressure Impactor yields higher values of mass concen-

tration.  This is due, at least in part, to the better collection charac-

teristics of the Low Pressure Impactor for large particles.

-------
                                                                   43
               SUMMARY  AND CONCLUSIONS








        Although the cascade impactor has been a useful tool in the





measurement of aerosol mass-size distribution, most systems in





current use  are limited to a usable lower particle size limit of





approximately 0.4 micrometers.   However,  operation  of specially





designed  impactors at reduced pressures can extend this lower limit.





In the present study a Low pressure Impactor system has been de-





signed, fabricated and tested which has a particle cutpoint size for





the last stage of 0.05 micrometers for particles of density = 2 gm/cm3.





        The impactor has four stages  which operate  at atmospheric





pressure and separate particles into fractions with size ranges of





>9.7,  5.0-9.7,  2. 46-5. 0 and 1. 21-2. 46  micrometers.  These are





followed by three stages and an after-filter which separate  the  aersol





into size  intervals of 0. 36-1. 21, 0.14-0.36,  0. 05-0. 36 and   <.. 0. 05





micrometers.





        Laboratory  testing  was performed to  verify the predicted





cutpoints and to evaluate the performance-limiting characteristics





of a) wall losses  b) particle rebound  from collection  surface  and





c) collected  deposit re-entrainment (mass loading limitation).  The





results of these experiments  confirmed the predicted  cutpoints of





the stages which were tested.  Data points for the tests are  shown





in Figure 8 superimposed upon a curve which represents the calculated




cutpoint values.

-------
                                                                   44







        Wall losses for the entire system were shown to be less than




6 percent when tested with aerosols of 0. 3 and 0. 6 micrometers





median diameter which had geometric  standard deviations of 3.





Initial tests with the upper stages indicated that substantial wall losses




resulted when the stages were used to  sample large particles.   A





re-design of the first two stages reduced these losses by 2/3; the total





loss for these stages,  when tested with 6. 1 micrometer diameter




aerosol, is now 10. 7 percent.





        Tests with the last stage  of the  low pressure  section, a stage





which has a normal jet velocity of 4160 cm/sec,  indicate that particle




rebound from the collection surface is  not  a significant problem.  In





these tests,  the jet velocity was  increased to over  7000  cm/sec while




the other impaction parameters were adjusted  in such a manner that





the predicted collection efficiency with the  test aerosol would remain





nearly constant.  Even at this high value of velocity,  there was  no




reduction in the efficiency of the stage  which demonstrates that  a





substantial fraction of  the particulate matter did not  bounce  off of





the collection media during the impaction process.





        The last impaction stage  of the  low pressure  section has design




parameters (high velocity and small jet sizes) which  make it the most





vulnerable of the low pressure stages to re-entrainment of collected





deposits.  This-phenomenon is observed to occur in impactors when





substantial deposits  are collected on a given stage.   Portions of the

-------
                                                                    45







deposits are subsequently eroded away during further sampling.  Tests





with the last low pressure stage showed no tendency for re-enlrainment





for deposits as large as 10 mg.





        The Low Pressure. Impactor system was operated  in parallel





with a standard Andersen non-viable  cascade impactor and used to





sample cigarette  smoke and atmospheric aerosol.  For cigarette





smoke, which  lias tew large particles,  the  agreement between data





obtained from  the two devices was excellent for particles  larger than





0.6 micrometers.  The Low Pressure Impactor showed a greater mass





fraction for the smaller sizes.   Tests with atmospheric aerosol





showed the Low Pressx;re  Impactor to yield larger fractions of small





( -•-. 0. 6 micrometer) particles and higher  overall values of aerosol





concentration.   In  one  case the  Low  Pressure  Impactor collected a





substantially greater qxiantity of larger (>7 micrometers) particles.

-------
                                                                  46

                            REFERENCES
 1.  Landsberg, H. ,  "Physical Climatology. " Znd edition, Gray,
     DuBois, Pennsylvania,  pp.  317-326(1958).

 2.  Robinson,  E. , "Effects of Air Pollution on Visibility." Air
     Pollution,  Chapter  11, Vol.  1, 2nd edition,  A, C.  Stern (ed. ),
     Academic  Press, New York,  349-400 (1968).

 3.  Holzworth, G. C. ,  "Some Effects of Air Pollution on Visibility
     in and near Cities. " Air Over Cities Symposium,  U. S. Dept.
     of Health,  Education and Welfare,  Robert A.  Taft Sanitary
     Engineering Center, Cincinnati,  Ohio, Technical Report
     A62-5, 69-88 (1961).

 4.  Hudson, J. D. , "Present Position of the Corrosion Committee's
     Field  Tests on Atmospheric Corrosion (Unpainted Specimens)."
     J. Iron Steel Institute, Vol. 148,  161-215(1943).

 5.  Czaja, A.  T. , "Uber das Problem  der Zementstaubwirkungen
     auf Pflanzen. " Staub, Vol 22, 228-232,  (1962).

 6.  Bohne, H.  , "Schadlichkeit von Staub aus Zimentwerken fur
     Waldbestande. "  Allgem. Forstz,  Vol. 18, 107-111(1963).

 7.  "Air Quality Criteria For Particulate Matter." U.S. Depart-
     ment of Health,  Education and Welfare, Public Health Service,
     Environmental Health Service, National Air Pollution Control
     Administration Publication  No.  AP-49,  129-144(1969).

 8.  "Deposition and  Retention Models for Internal Dosimetry of the
     Human Respiratory Tract." Task Group on Lung Dynamics
     Health Physics,  Vol.  12,  173-207(1966).

 9.  Findeisen, W. , "Uber das Absetzen Kleiner in der Luft
     suspendierten Leilchen in der menschlichen Lunge bei der
     Atmung."  Arc.  Ges. Physiol. ,  Vol. 236, 367-379 (1935).

10.  May,  K. R. , "The Cascade  Impactor; An Instrument for
     Sampling Coarse Aerosols," Journal of Scienctific Instruments,
     Vol. 22, 187-195 (1945).

11.  Ranz,  W. E. and Wong, J. B. ,  "Impaction of  Dust and Smoke
     Particles  on Surface and Body Collectors, " Industrial and
     Engineering Chemistry,  Vol.  44, 1371-1381  (1952).

-------
                                                                   47
12.   Andersen,  A. A. ,  "A Sampler for Respiratory Health Hazard
      Assessment,"  American Industrial Hygiene Association
      Journal,  Vol. 27, 11.  160-165,  1966.

13.   Mueller, P.K., Helwig,  H. L. ,  Alcocer,  A. E. ,  Gong, W. K. ,
      and Jones, E. E. , "Concentration of  Fine Particles and Lead
      in Car Exhaust."  American  Society  for Testing  and  Materials,
      Special Technical Publication 352, pp.  60-73, 1964.

14.   Lee, R. E. , Jr.,  Patterson,  R. K. ,  Crider, W. L. , and
      Wagman,  J. ,  "Concentration and  Particle Size Distribution
      of Particulate Emissions in Auto Exhaust,", Atm.  Env. 5,
      225-237 (1971).

15.   Stern,  S.C., Zeller, H. W. ,  Shekman, A. I. , "Collection
      Efficiency  of Jet Impactors at Reduced Pressures, "  Industrial
      and Engineering Chemistry Fundamentals, Vol.  1, No.  4
      pp.  273-277, 1962.

16.   McFarland, A. R.  , Zeller, H. W. , "Study of a large  volume
      impactor for high altitude aerosol collection. "  Report of  the
      Division of Technical Information Extension of  the USAEC,
      TID-18624,  1963.

17.   Buchholz, H. ,  "An Underpressure Impactor."  Staub-Reinhalt,
      Luft,  Vol.  30,  No. 4, 1970.

18.   Millikan, R. A. , "The general law of fall of a small spherical
      body through a gas and its bearing upon the  nature of molecular
      reflection from surfaces." Phys. Rev. 22, 1-23 (1923).

19.   Marple, V. A. ,  "A Fundamental Study of  Inertial Impactors."
      Ph.D.  Thesis, Univ. of Minn.  (1970).

20.   McGregor, F. R. , "Development of a Modified Andersen
      Impactor, " M. S.  Thesis,  Univ. of Notre Dame,  (1971).

-------
                                   TECHNICAL REPORT DATA
                            (Please read Instructions on the reverse before completing)
 1. REPORT NO.
  EPA-650/2-74-014
                                                           3. RECIPIENT'S ACCESSION«NO.
4. TITLE AND SUBTITLE
                                                           5. REPORT DATE
                                                             October 1973
  Development of a  Low  Pressure Impactor
                                                           6. PERFORMING ORGANIZATION CODE
T. AUTHOR(S)
  A.  R.  McFarland,
  H.  S.  Nye and C. H.  Erickson
             8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
                                                           10. PROGRAM ELEMENT NO.
  Anderson 2000 Inc.
  P.  0.  Box 20769
  Atlanta, Ga.  30320
               1A101C
             11. CONTRACT/GRANT NO.


               68-02-0563
 12. SPONSORING AGENCY NAME AND ADDRESS

  Environmental Protection  Agency
  Natioanl  Environmental  Research Center
  Research  Triangle Park, N.  C.
             13. TYPE OF REPORT AND PERIOD COVERED
             14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
16. ABSTRACT
      A Low Pressure Impactor  aerosol  sampler was designed  fabricated and tested.  The
 system injects a fixed aerosol  flow  rate of 1 cfm at  inlet  conditions and causes the
 particulate matter to be separated  and collected on four  atmospheric pressure and
 three  reduced pressure impaction  stages and an after-filter.   Outpoint sizes of the
 stages are 9.7, 5.0, 2.46, 1.21,  0.355, 0.141, and 0.05 micrometers for spherical
 particles with a density of  2  gm/cm  .   Each of the impaction  stages is fitted with a
 glass  fiber media collection substrate to facilitate  gravimetric analysis of the
 collected samples.

      Experiments conducted with  laboratory aerosols show the system to have wall losses
 less  than 6 percent when the mass median diameter of  the  aerosol is 0.6 micrometers.
 For  particles 6.1 microns in size, the wall losses on the upper stages are less than
 11 percent.   Both particle rebound and re-entrainment from  the collection surfaces
 are  shown to be negligible.  Each low  pressure stage  can  be loaded with more than
 10 mg  of  deposited aerosol without re-entrainment occurring.
17.
                                KEY WORDS AND DOCUMENT ANALYSIS
                  DESCRIPTORS
                                              b.lDENTIFIERS/OPEN ENDED TERMS
 Aerosol  Sampler
 Low Pressure  Impactor
 Re-Entrainment
 Particle Sizing
 Sub-Mi cron
                           c.  COSATI Held/Group
18. DISTRIBUTION STATEMENT

 Release Unlimited
19. SECURITY CLASS (This Report)
  Unclassified
                                                                         21. NO. OF PAGES
54
                                              20. SECURITY CLASS (Thispage)
                                                Unclassified
                                                                        22. PRICE
EPA Form 2220-1 (9-73)

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