United States
               Environmental Protection
               Agency
Atmospheric Research and Exposure
Assesment Laboratory
Research Triangle Park NC 27711
               Research and Development
EPA/600/S3-90/048 Sept. 1990
EPA       Project  Summary
                Development of a  Sampling
                Procedure for  Large  Nitrogen-
                and Sulfur-Bearing  Aerosols
               Stephen J. Randtke, Dennis p. Lane, and Terry E. Baxter
                   The objective of this research project
               was to develop a procedure that would
               permit accurate sampling and analysis
               of large (>2.5 urn) aerosols, especially
               those containing nitrate, ammonium, and
               sulfate, without interfering with the
               sampling and analysis of the gases and
               fine particle species of interest In dry
               deposition and acid aerosol sampling.
               Although other sampling devices were
               initially considered, the  experimental
               work focused exclusively on a single-
               stage Impactor modified to utilize  a re-
               movable impaction surface mounted on
               the end of an annular denuder.
                   The cut point of the modified Impac-
               tor, used with a polycarbonate (PC) filter
               coated with 5 |iL of silicone oil, was 2.5
               \an, with less than 1% particle bounce
               occurring for 8-^.m particles. Significant
               particle bounce occurred when using
               uncoated or grease-coated impaction
               surfaces composed of PTFE or porous
               glass. Saturating a porous glass impac-
               tion disk with oil reduced particle bounce
               to about 2%, but the impacted particles
               could not be easily removed from the
                porous glass impaction surface.
                   Non-isoaxial sampling resulted in
                substantial undersampling.  Isoaxial
                sampling of ambient air requires either a
                horizontally mounted sampling system
                or a vertically mounted system with an
                inlet bend.  Horizontal  configurations
                performed poorly; greased and lightly
                oiled surfaces exhibited a high degree of
                bounce and oil flowed sideways off oil-
                saturated  disks.   Vertically mounted
                systems employing a bent-tube  inlet
                performed reasonably well, but  inlet
losses were quite high for very large
particles and for blunt-tipped Inlets. Inlet
losses averaged only 2.7% for 7.9-(im
uranine particles sampled using a sharp-
edged 90° bent-tube Inlet.
    Losses of solid particles within the
combined impactor/denuder system
were greatest for particles close in size
to the cut point. For particles having an
aerodynamic diameter of 2.0-2.8  |im,
losses in the denuder ranged from 4-8%
of the mass sampled, while losses on the
spacer between  the impactor and de-
nuder ranged from 10-17% of the mass
sampled. Losses for particles of other
sizes (larger and smaller) were generally
negligible (i.e., <1%).
    A number of oils and greases were
found to be compatible with the analysis
of impacted particles by ion chromatog-
raphy. PC filters were found to be free of
nitrate, nitrite, and sulfate.  PC filters,
silicone oil, and Vaseline exposed to
high concentrations of HNO3 and SO2
were found to adsorb little, if any, nitrate
or sulfate.  TFE impaction disks may
adsorb traces of HNO3, but it is not nec-
essary to include them in the analysis if
they are overlain by a PC filter.
    Impacted particles of varying com-
position were exposed to high concen-
trations of potentially reactive  gases
(HNO3, SO2, or NH) for four hours at a
nominal flowrate of 16.7 Lpm. NH4CI and
NH4NO3 impacted on an uncoated  PC
filter did not volatilize when exposed to
purified air.  NH Cl and NaCI particles
 Impacted on a sllicone-greased PC filter
did not react with SO2. NaCI and NH4NO,
particles impacted on a PC filter coated

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 with flvauL of silicons oil did not react to
 a significant extent with  HNO or SO.,
 respectively.  Acidic NaHSO3 particles
 Impacted on a greased surface reacted
 to a limited extent with NH, (i.e., they wore
 1.7 to 3.5% neutralized).
     In a 24-hour field test employing
 four collocated sampling systems, the
 concentrations of coarse-particle nitrate-
 N and sulfate were determined to be
 0.939 ± 0.032 u,g/m*(± 3.4%) and 0.222
 ± 0.007 u.g/m3 (±  3.3%),  respectively.
 However, substantial percentages of the
 nitrate, sulfate,  and ammonium (36%,
 44%, and 50%, respectively) were col-
 lected on the bent-tube Inlets rather than
 on the Impactlon disks.
     This Project Summary was  devel-
 oped by EPA's Atmospheric Research
 and Exposure Assessment Laboratory,
 Research Triangle Park,   NC,   to an-
 nounce key findings of  the  research
 project that Is fully documented In a
 separate report of the same  title (see
 Project Report ordering Information at
 back).

 introduction
    So that reliable estimates of the loads
 of nitrogen and sulfur associated with dry
 deposition can be made, scientists at the
 U.S. EPA and elsewhere have been work-
 ing to  develop quantitative  methods to
 sample and  analyze  the major nitrogen-
 and sulfur-containing species present in
 gaseous and aerosol form in ambient air.
 These include HNO3, HNO,,  NO, NO,, NH,.
 n'rtrate, nitrite, ammonium, SO,, SO, H,SO.,
 sulfate, and sulfite.
    Progress in developing sampling
 methods for dry deposition has been ham-
 pered  by  the chemical complexity  of the
 system; several of the chemical species of
 interest are  quite reactive and there are
 interactions between the solid, liquid, and
 gaseous components.  As a result, a con-
 siderable  number of artifacts have been
 encountered, including: 1)  adsorption of
 gaseous species (e.g., HNO3 and SO2) on
 thefittermediaorthe sampling device used
 to collect aerosols; 2) adsorption of HNO3
 and other gaseous species by particles
 deposited on the filter media; 3) volatiliza-
 tion of paniculate species such as NH.NO3
 and NH4CI; 4) and formation  and subse-
 quent volatilization of HNO3 as a result of
 metathetfcal or displacement reactions. A
 number of investigators have been working
to develop sampling devices and procedures
able to circumvent these problems.
    One system currently under develop-
ment and potentially able to circumvent
these problems consists of a filter pack
preceded by one or more annular denuders
 and a Teflon-coated glass impactor (Figure
 1).  The filter pack is designed to capture
 fine particles and any gases that may vola-
 tilize from them, while the denuders capture
 reactive gases and allow fine particles to
 pass through unaltered into the filter pack.
. The impactor is designed to remove large
 particles (i.e., those having an aerodynamic
 diameter greater than 2 u.m), which might
 otherwise be trapped in the denuder or
 which, if they were alkaline, might neutralize
 acidic aerosols captured by the filter pack.
     Initial attempts to circumvent the prob-
 lems associated  with large particles have
 focused on the use of either a Teflon-coated
 glass impactororaTef Ion cycloneto remove
 large particles ahead of the first denuder
 tube. However, there are potential problems
 with each of these devices, including: 1)
 particle resuspensipn or bounce, especially
 at high mass loadings; 2) volatilization of
          constituents of interest from the surfaces of
          large particles; and 3) reactions of gaseous
          constituents with impacted particles, with
          thesampling device itself, orwith any grease
          oroilusedtotraptheparticles. Furthermore,
          neither device is inherently well suited to
          analysis of the large particle fraction, which
          would  be highly desirable in view  of its
          potential significance. Although particulate
          sulfate is "primarily  associated  with fine
          particles,  large particles can  be very sig-
          nificant in terms of total particle mass, par-
          ticulate nitrate, and particulate ammonium.
             The objective of this investigation was
          to develop a sampling procedure for large
          aerosols that would: 1) permit accurate de-
          termination of the mass and chemical com-
          position of large particles present in ambi-
          ent air over a 24-hour period; 2)  employ a
          device that could be used in conjunction
          with an annular  denuder and filter pack
     Couplers
  PTFE/FEP-Coated Bent-Tube Inlet



  TFE Sleeve Coupler


 PTFE/FEP-Coated Glass-lmpactor Nozzle (4.0 mm)



 Silicone-Rubber-Filled TFE Spacer


 TFE Impaction Disk


• Annular Denuder with Pedestal
 (Coated with Sodium Carbonate)






 2nd Annular Denuder (Coated with Citric Acid)




3-Stage TFE Filter Pack




                     Mass Flow Controller
                                                          To Vacuum


  Figure 1.   Glass-impactor annular-denuder filter-pack sampling system.

                   2

-------
without interference in the determination of
the gaseous and fine-particle constituents;
3) avoid the formation of chemical artifacts;
and 4) be simple enough  to deploy in  a
nationwide monitoring network.
    Although other sampling devices were
initially considered, the experimental work
focused exclusively on a single-stage im-
pactor modified to utilize a removable im-
paction surface mounted on the end of the
first  annular denuder (Figure  1).  This
modified design was conceived by re-
searchers at the University of Kansas and
designed and constructed  (in cooperation
with  University Research Glassware,
Carrboro, NC)  as part of another project
previously funded by the U.S. EPA.  Al-
though it had not yet been fully character-
ized, it was subsequently incorporated into
sampling systems being used by several
other teams of investigators.
    Experiments were conducted to exam-
ine: the cut point of the modified impactor;
impactor inlet losses; particle bounce utiliz-
ing various impaction surfaces and impac-
tion-surface coatings;  horizontal versus
vertical mounting; collection efficiency as a
function of mass loading;  particle deposi-
tion  patterns; the compatibility of various
oils and greases with chemical analysis of
impacted particles; the reactivity of various
oils, greases, and impaction surfaces with
gases (SO,,, HNO3, and NH3); the volatility
 and reactivity of impacted particles on coated
 and uncoated surfaces; and the precision of
the method underfield sampling conditions.

 Procedure

     A.  Sampling System Components
     The sampling system (Figure 1) con-
 sisted of the modified impactor coupled to a
 bent-tube inlet (ASTM method D3685-78)
 and the annular-denuderfilter-pack assem-
 bly previously described by Vossler et al.
 (Atmos. Environ., 22,8,1729-1736,1988).
     Several types of impaction disks were
 used. The most successful impaction disk
 (Figure 2) was machined  from virgin TFE
 and featured a small (77-u.L) "well" 14 mm
 wide  and 0.5 mm  deep.   This well was
 designed to accept either a small pool of oil
 (underlain by a 13-mm PC membrane filter)
 or an oiled or greased 13-mm membrane or
 glass-fiber -filter.   l| was  most frequently
 used with a silicone-oiled PC (Nuclepore)
 filter, which was found to migrate if placed
 on a flat impaction surface. Disks fitted with
 a coarse 10-mm fritted (porous) glass disk
 were also used.
      B.  Oils and Greases
      Four greases and three oils were  se-
 lected for study: petroleum jelly (Vaseline);
 high-vacuum silicone grease  (Dow Corn-
            	  16 mm

            •i	  14 mm
                                          0.5 mm
       p
                           	5.75 mm-

  Figure 2.'  TFE impaction disk with well.


ing); Halocarbon grease, type 25-5S (Halo-
carbon Products Corp.); Fluorolube grease,
type GR-290 (Hooker Chemical Co.); sili-
.cone diffusion-pump oil (type 704,  Dow
Corning Corp.);  and  two  mineral  oils
(Fisherbrand  19 and Duo Seal).
     C. Analytical Methods
     Anions were determined by ion chro-
matography;  ammonium was determined
using an Alpkem continuous flow analyzer;
and uranine  was  determined using a flu-
orometer.  Oiled  and greased  impaction
surfaces were extracted with pentane and
then reagent water; and the aqueous phase
was subsequently analyzed for the con-
stituents of interest.
     D.  Particle Generation and Impac-
        tion
     Particles were generated using a Ber-
glund-Liu  Monodisperse Aerosol Genera-
tor equipped with a Krypton-85 charge neu-
tralizer. The  size, shape, and uniformity of
the particles were verified by scanning elec-
tron microscopy (SEM). Particles spanning
asize range of < 1 u.m to 30 u.m and particles
composed of  uranine, NHLCI, NH4NO3,
(NH4)2SO4, NaCI, and NaHSO4 were used
                                                             2.5 mm
                                                               t   i
                                                                      5 mm
                       1.5 mm
                                                                      10 mm
over the course of the investigation.  Par-
ticles generated in the laboratory were im-
pacted by inserting the impactor inlet (with
or without the bent-tube inlet) into either a
wind tunnel or a small-diameter plastic pipe
into which the particles had been introduced.
The  wind tunnel was  used for low mass
loadings  and the pipe was used for high
mass loadings.
    E.  Preparation of Impaction Surfaces
    After scrupulous cleaning, impaction
disks were prepared for use in one of the
following ways:   1)  oiled PC filters  were
prepared by carefully placing a clean 13-
mm, 0.4-u.m-pore filter in the well and then
placing the desired amount of oil (usually 5
u.L of silicone oil) on  top of the filter; 2)
uncoated  PC filters  were held in place by
first  adding a very  small dab  of silicone
grease to the top of the impaction disk; 3)
greased  membrane filters  were prepared
by placing ten 50-u.L portions of a 1% solu-
tion of grease (usually silicone) in pentane
on top of the filter, allowing the solvent to
evaporate after adding each 50-u.L portion;
4) greased impaction disks were prepared
as described in  item 3, omitting the filter;
and  5) oiled fritted  glass disks were pre-

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                                    Bell Connectors
                              (To Mount Optional Denude~r)
       Norprene
          Tubing

  Air
Purifier
            47-mm
  Filter       Filter

      Ambient
="-<	 Mr —
                      Air        «Red«
                    Purifier     Coupler
                                                          1/4" FEP
                                                       1/8" TFE
                     TFE Sleeve
                frnpactor Nozzle

                    TFE Spacer

                 Impaction Disk
               Annular Denuder





                 Bell Connector


               2-Way Valve (SS)
               Bypass Line
            (Norprene Tubing)
                                      3-Way
                                    Valve (SS)
                                                 TEE(SS)
                                                   1/4"
                                                  ~FEP~
2 5-mm
 Filter
                                                                                    Microvalve
                                                                  Reservoir
                                                                                               A/2@ 5 PSI
                                                                                        Vacuum
                       Figure 3.  Impaction-surface exposure system.

-------
pared by adding oil dropwiseto saturate the
disk or adding a fixed  amount of oil in a
pentane solution  as described  in item 3
above.
    F.  Tests for Chemical Artifact
        Formation
    Oils, greases, impaction surfaces, and
impacted particles were exposed to various
gases (SO2, HNO?, NH3, or purified air) by
placing an appropriately prepared specimen
into an impaction-surface exposure system
(Figure  3) or an impacted-particle expo-
sure system (similar to the system shown in
Figure  3,  except that  a control sample
without  particles was  exposed simulta-
neously with the particles). A side-stream of
nitrogen, carrying the reactive gas of inter-
est, was introduced through  a  stainless-
steel Swagelock tee. A solution of HNO3
and H2SO4 was used to generate HNO3
vapor; a solution of NH4OH was used  to
generate NH3 vapor; and a solution of H2SO3
and KH2PO4 was used to generate SO2
vapor.
    G.  Field Test
    A 24-hr field test  was conducted  to
determine the precision of the method. Four
identical sampling systems were mounted
on the roof of afour-story building (Learned
Hall) on the campus of  Kansas University.
The bent-tube  inlets were turned  in the
direction of the prevailing wind  (north  to
northwest) on the day of sampling.  Mass
flow controllers having an accuracy of ±1 %
and a precision of ± 0.2%, were used  to
maintain a flow of 12.5 Lpm (STP: 25°C and
1 atm); prior to use they were cross-cali-
brated and found to  agree within 0.5%.

Results and Discussion
    A.  Physical Performance
        Characteistics of the Modified
        Impactor
    The use of an oil-saturated  impaction
surface dictates a vertical impactor orien-
tation (to prevent oil from dripping off),
whereas the use of greaseorathin film of oil
allows either a vertical or a horizontal ori-
entation to be used.  In the latter case,
particle bounce may occur at high mass
loadings. Since ambient winds are gener-
ally horizontal or nearly so, non-isoaxial
sampling conditions will exist when the im-
pactor is used in the vertical position, and
particles may be elutriated. A 90° bend can
be used with a vertically positioned impac-
tor to sample isoaxially  and thus eliminate
the elutriation effect, but the inlet  bend
presents an additional surface where par-
ticle deposition and chemical artifact forma-
tion may occur. Thus, regardless of which
impaction surface coating is used, its influ-
ence on the orientation, performance, and
operation of the impactor must be consid-
ered.
    To gain insight into certain aspects of
the impactor's physical performance char-
acteristics, experiments were conducted to
examine:  1) the cut-point of the modified
impactor; 2) particle collection  efficiency
under non-isoaxial sampling conditions; 3)
inlet losses as a function of particle size;
and 4) particle bounce as afunction of mass
loading and impaction surface type.  These
experiments were not intended to provide a
comprehensive solution to the age-old large-
particle  sampling problem.   Rather, they
were intended to characterize the physical
performance  (and limitations) of the  im-
pactor, to aid in the conduct and interpre-
tation of subsequent experiments address-
ing chemical  artifact formation, to  reveal
problems requiring further investigation, and
most of all to determine the size of particles
that could be successfully sampled.
    The cut point of the modified impactor,
when used with a PC membranef iltercoated
with 5 |o.L of silicone oil, was experimentally
            determined to be 2.5 u.m, with less than 1%
            particle bounce for 8-u.m particles.  Signifi-
            cant particle bounce was found to occur
            when using uncoated or grease-coated im-
            paction surfaces or  when using a porous
            glass impaction surface (Figure 4). Satu-
            rating a porous glass impaction disk with oil
            reduced particle bounce to about 2%, but
            the impacted particles could not be easily
            removed from the porous glass impaction
            surface.   Sudden increases  in flowrate
            caused impacted particles to be dislodged
            from uncoated or greased surfaces.
                Non-isoaxial sampling resulted in sub-
            stantial undersampling of large particles, so
            isoaxial sampling (perhaps using a vane-
            mounted system) appears to be a necessity.
            Iso'axial sampling of ambient  air requires
            either a horizontally mounted sampling sys-
            tem or a vertically mounted system with an
            inlet bend. The horizontal configurations
            tested performed poorly; greased and lightly
            oiled surfaces exhibited a high degree of
            particle bounce and oil tended to flow side-
            ways off oil-saturated disks.   Vertically
            mounted systems employing a 90° bent-
          100


           90


           80


           70
             T
                 T
                     T
                              =T
                                  =T
Upright, Membrane Filter, 5 \iL Si Oil
Inverted, Porous Glass Dish, Mineral Oil (Sat'd)
Inverted, Porous Glass Disk, 50 pi. SI Oil
Inverted, Porous Glass Disk, 20 \iL Si Oil
Upright, Porous Glass Disk, 20 pi. SI Oil
                                 WOO                  2000
                              Mass of Uranine Sampled, micrograrns
                                              3000
 Figure 4.  Impactor collection efficiency as a function of mass loading for solid 7.9-y.m
           uranine particles.

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tuba \n\Q\ performed reasonably well, but
Inlet losses were quite high for very large
particles (e.g., 91 to 96%for26.5-u.muranine
particles) and for blunt-tipped inlets (e.g., 7-
14%for8-u,muranineparticles). Inletlosses
averaged only 2.7% for 7.9  urn uranine
particles sampled using asharp-edged bent-
tube Inlet in an upright position; the pattern
of the deposited particles indicated the
presence of a double vortexing flow condi-
tion, which did not appear to adversely
affect impactor performance.
     Losses of solid particles within the
combined impactor denuder  system (ex-
cluding the inlet) were greatest for particles
aboutthesizeofthecut point (Figures). For
particles having an aerodynamic diameter
of 2.0-2.8 urn, losses in the denuder ranged
        from 4-8% of the mass sampled, while losses
        on the spacer between the impactor and
        denuder ranged from 10-17% of the mass
        sampled. However, losses for particles of
        othersizes (largerand smaller) weregener-
        ally negligible (i.e., <1%).
            B.  Tests for Chemical Artifact
                Formation
            Selected oils and greases that might
        be used to prevent particle bounce were
        examined.and experiments were conducted
        on the most promising candidates to de-
        termine: 1) their purity; 2) their compatibility
        with analysis of trace anions by ion chro-
        matography; 3) their gravimetric stability; 4)
        their ability to react with gaseous constitu-
        ents to form chemical artifacts; and 5) their
          100
           80
           70
           60
           50
            30
            20
+ Passing Impaction Disk

• Loss on Spacer

A. Loss In Denuder
                           2345      678

                             Particle Aerodynamic Diameter, microns
                                                                           to
ability to prevent reactions that might occur
between reactive gasses and  impacted
particles.
    A  number of oils and greases were
found to be compatible with the analysis of
impacted particles using ion chromatogra-
phy, i.e., the anions of  interest were not
leached or sorbed, impacted particles ap-
peared to be completely extracted, and no
interfering peaks were observed. PC filters
were found to be free of nitrate, nitrite, and
sulfate. PC filters, siliconeoil, and Vaseline
exposed to high concentrations of HNO3
and SO2 were found to adsorb little, if any,
nitrate or sulfate. TFE impaction disks may
adsorb HNO3; but there is no need to ana-
lyze them, since the overlying  impaction
filters can readily be removed for analysis.
    NH4CI and NH NO3 particles impacted
on  an  uncoated PC filter did not volatilize
when  exposed to purified air.  Impacted
particles of varying  composition were im-
pacted on uncoated, greased, or oiled sur-
faces  and  subsequently exposed  to high
concentrations of potentially reactive gases
(HNO3, SO2, or NH3) at room temperature
and low relative humidity for four hours at a
nominal flowrate of  16.7 Lpm.   Table  1
summarizes the results.
     It  should be noted that there may have
been particles on the rims of the impaction
disks exposed prior to August 18; and par-
ticles may have been physically dislodged
from the disks by the force of the jet prior to
August 23, after which a "soft-start" proce-
dure was implemented. Considering only
those  samples exposed after August 23, it
can be seen that: 1) NaCI particles impacted
on oiled orgreased filters reacted only slightly
with HNO3; 2) NH4CI and NaCI particles
impacted on uncoated and greased filters,
respectively, did not react with SO2> nor did
NH4NO3 particles impacted on an uncoated
filter; 3) NH Cl particles impacted on greased
filters  reacted to only a very limited extent
with HNO3; and 4) acidic NaHSO4 particles
impacted on greased filters were  partially
(1.7 to 3.5%) converted to NaNH4SO4 by
reaction with NH3.
     C.  Field Test
     In a 24-hour field test employing four
collocated sampling systems, the concen-
trations of coarse-particle nitrate-N and sul-
fate were determined to be 0.939 ± 0.032
u.g/m3 (± 3.4%) and 0.222 ± 0.007 u.g/m3 (±
3.3%), respectively. However, substantial
percentages of the nitrate,  sulfate, and
ammonium (36%, 44%, and 50%, respec-
tively) were collected on the bent-tube inlets
 rather than on the impaction disks.
 Figure 5.  Particle tosses on the spacer and in the denuder as a function of particle size.

                                                              6

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Conclusions
    1.   The cut point of the modified im-
        pactorwas experimentally deter-
        mined  to be 2.5 u.m, identical to
        its theoretical outpoint.
    2.   Non-isoaxialsampling resulted in
        a  substantial reduction in sam-
        pling efficiency,  with less than
10% of 8-(4.m particles entering
an  inlet orthogonal to the air
stream.  Accurate  sampling in
the field will require isoaxial sam-
pling.
When  the  samplers  were
mounted horizontally, minus the
bent-tube inlets, significant frac-
4.
tions (2.0-9.0%)  of  8.34-jim
uranine particles were collected
in the  impactor inlets,  presum-
ably as a result  of sedimentation
or turbulent diffusion.
Extensive particle bounce oc-
curred   when  using uncoated
impaction surfaces. Hence, oil or
Table 1.  Summary of Particle Reactivity Experiments*
Date
(1988^
8/01
8/02
8/03
8/04
8/05
8/09
8/09
8/12
8/15
8/16
8/18
8/19
8/22
8/23
8/31
9/07
9/14
9/21
9/28
ft /Ort
9/30
10/03
10/07
10/07
10/12
10/12
10/21
10/28
11/04
11/11
11/18
11/25
12/01
Particle
Iwaa
NH4CI
NH4CI
NH4CI
NH4CI
NH4CI
NH4CI
NH4CI
NaCI
NaCI
NaCI
After this date,
NaCI
NaCI
Particle Oil or
Mass. u.g Grease
62.2 None
87.0 None
129.4
106.8
74.0
83.4
32.7
26.8
148.4
70.9
impacted
239.7
389.8
Oil
Oil
Oil
Grease
Grease
None
Oil
Grease
Test Gas
Type ng/m3
HNO3 338
HNO3 318
HN03317
HN03 301
HNO3 343
HNO3 328
HN03114
HN03 341
HNO3 340
HN03 320
particles were transferred to a fresh TFE
Oil
Oil
After this date, the "soft start" procedure was
NaCI
NACI
NACI
NaCI
10.9
41.6
58.9
94.1
Oil
Oil
Oil
Oil
HNO3 304
HNO3 307
used.
HN03 30.1
HN03 60.0
HN03 71.0
HNO3 58.1
Mass Found
on Disk, ng
2.57 (N03-N)
3.13(NO3-N)
0.17(N03-N)
0.48 (NO3-N)
0.00 (NO3-N)
0.93 (NO3-N)
2.88 (NO3-N)
1.57(NO3-N)
0.72 (NO3-N)
2.83 (N03-N)
impaction disk prior to
3.08 (N03-N)
2.94 (N03-N)

0.03 (NO3-N)
0.10 (NO3-N)
0.11 (NO3-N)
0.26 (N03-N)
Displacement to Denuder
JPJ1 %. B.
Chloride 27.5 1.74
Chloride 24.6 1.79
Chloride
Chloride
Chloride
Chloride
Chloride
Chloride
Chloride
Chloride
exposure.
Chloride
Chloride

Chloride
Chloride
Chloride
Chloride
1.5
3.2
0.9
63.9
48.5
43.2
2.3
14.7

5.6
2.7

0.00
1.0
0.58
1.3
3.10
1.86

15.07
1.44
1.77
1.14
1.04

1.11
0.88

0.00
1.03
0.93
1.11
After this date, afresh citric-acid-coated denuder was used to scrub the inlet air when N-containing particles were exposed.
NH.NO,
• 4 J
NH4NO3
NH4NO3
NH4N03
NH4CI
NH4CI
NaCI
NaCI
NaCI
NH4CI
NH4CI
NaHSO4
NaHS04
199.9
20.1
208.6
298.8
78.4
46.8
159.7
207.6
190.6
72.6
163.0
461.9
495.0
Oil
None
None
None
None
None
Grease
Grease
Grease
Grease
Grease
Grease
Grease
SO2 371
SO2 337
SO2 486
Air —
SO2 452
Air —
SO2 375
HN03101
HN03118
HN03 139
HN03 125
NH3 39.8
NH3 114
0.11(SO4)
0.00 (SO4)
0.00 (SO4)
NA
0.00 (SO4)
NA
0.00 (S04)
0.33 (NO3-N)
0.73 (NO3-N)
1.48(N03-N)
1.06(N03-N)
1.90{NH4-N)
1.00(NH4-N)
Nitrate
Nitrate
Nitrate
Nitrate
Chloride
Chloride
Chloride
Chloride
Chloride
Chloride
Chloride
0.00
0.00
0.67
0.11
4.8
3.6
0.50
0.45
1.34
7.43
0.00
(3.5%toNaNH4S04)
(1.7%toNaNH4So4)
0.00


NA

NA

0.66
0.84
0.96
0.00

     Particle mass = initial mass on particles on the impaction disk; oil =silicone oil; grease = high-vacuum silicone grease; R is the control-
     corrected raiio of moles of ion displaced to moles of contaminant ion found on the impaction filter; NA = not applicable

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    grease must be used to prevent
    particle bounce.
5.  When using a silicone-greased
    impaction  surface, significant
    particle  bounce occurred at a
    uranine-particle mass loading of
    only 38 u.g, about 70% of a mono-
    layer.  Hence, use of silicone
    grease will limit mass loadingsto
    very low levels unless a rotating
    surf ace or other means of  reduc-
    ing the mass of particles per unit
    area is developed.
6.  Using a porous glass impaction
    surface  coated with 50 uL of
    silicone oil, 27-29% of the  par-
    ticle mass bounced off the im-
    paction surface when sampling
    7.9-u.m uranine particles  at a
    mass  loading of  only 4-5  |ig.
    Saturating the porous glass sur-
    face with mineral oil reduced
    particle bounce to approximately
    2% of the  particle mass sam-
    pled. Under severe  mass load-
    ing conditions (126-2,920 u.g),
    only about 1% bounce was  ob-
     served using  a PC filter coated
     with only 5 \iL of silicone oil.
 7.  Since excessive bounce  oc-
     curred with uncoated, greased,
     or lightly  oiled impaction  sur-
     faces, and since the oil tended to
     flow sideways off oil-saturated
     porous glass impactions disks
     when the sampling system  was
     horizontally mounted, it was de-
     termined that isoaxial sampling
     could best be accomplished us-
     ing a vertically mounted system
     with a bent-tube inlet.
  8.  Inlet losses were observed to be
     91 to 96% for 26.5-u.m  uranine
     particles  sampled using sharp-
     edged 90° bent-tube  inlets, 48-
     52% for  15.2-u.m ammonium-
     suifate particles  sampled using
     bent-tube inlets constructed from
     thin-walled glass tubing, 7-14%
     for  8-u,m uranine  particles
     sampled  using  blunt 90° bent-
     tube inlets, 3.7-9.5% for 7.9-u.m
     uranine particles  sampled using
     sharp-edged 90° bent-tube inlets
     in an inverted position, and  0.5-
     5.3% (averaging 2.7%) for 7.9-
     ]im uranine particles sampled
     using sharp-edged 90° bent-tube
     inlets in  an upright position.
  9.  For 7.9-u.m uranine  particles, at
      least 12-15% of the total particle
      mass   sampled  using  an  oiled
      porous glass impaction surface
    became  entrapped within the
    pores and was not readily ex-
    tractable for subsequent chemi-
    cal  analysis.  Uranine particles
    collected on oiled membrane fil-
    ters were readily extracted.
10. Deposition of 7.9-u.m  uranine
    particles collected on a silicone-
    oiled PC filter indicated the pres-
    ence of a double-vortexing flow
    condition,  presumably resulting
    from the use of the bent-tube in-
    let.  The particle collection char-
    acteristics of the  impactordonot
    appear to be adversely affected
    by this condition.
11. Particle losses in the combined
    impactor-denuder system (ex-
    clusive of the inlet losses) were
    found  to occur  predominantly
    with particles about the size of
    the  impactor's cut-point  diam-
    eter. Within the denuder,  losses
    of particles having  an aerody-
    namic  diameter of 2.0-2.8 u.m
    ranged from  4-8% of  the total
    mass  sampled.  Particles were
    also lost on the TFE  spacer be-
    tween the impactor and the de-
    nuder, representing  10-17% of
    the mass sampled for 2.0-2.8 u.m
    particles.   Losses of particles
    having other  aerodynamic diam-
    eters were negligible.
 12. Analysisoffourgreasesand three
    oils revealed that they were of
    suitable purity and were compat-
     ible with analysis of trace con-
    centrations of anions by  ion
     chromatography after extraction
     with pentane and water. They did
     not generally leach or sorb sig-
     nificant amounts of the anions of
     interest.  The mineral oils were
     found to contain detectable
     amounts of  extractable  sulfate,
     but not enough  to be significant
     when a  small quantity of oil is
     used  in a 24-hour test.
 13. Silicone oil  and Vaseline  ap-
     peared   to be  compatible with
     gravimetric analysis of impacted
     particle mass.   However, gravi-
     metric analysis would only be
     useful for high  mass   loadings
     (i.e.,  those for  which weighing
     would give reasonably accurate
     results),  a dust-free  weighing
     room might be needed, and addi-
     tional testing is needed to  de-
     termine  how long  the samples
     must be equilibrated prior to
     weighing.
                                                           8
  14. PC filters were found to be free
      of nitrate, nitrite, and sulfate; but
      mixed-fiber  (cellulose acetate/
      cellulose nitrate) filters contained
      measurable  amounts  of  leach-
      able nitrate.
  15. Silicone oil,  PC  filters, and
      Vaseline exposed to HNO3 and
      SO2 were found to sorb little if
      any nitrate or sulfate. The traces
      of nitrate and sulfate which were
      often detected in exposed speci-
      mens may very well have been
      due to  handling rather  than to
      chemical artifact formation; and
      the  amounts detected  would
      generally not  be significant for
      samples collected over a  24-
      hour period.
   16. TFE impaction disks may adsorb
      traces of HNO ; but it is not nec-
      essary  to analyze the TFE disk
      when it is overlain  by a PC filter.
   17. NH4CI and NH4NO particles im-
      pacted on uncoated PC filters did
       not volatilize from the collection
      surface when exposed to purified
       air.
   18.  NH4CI, NaCI,  and  NH4NO3 par-
       ticles impacted on uncoated or
       greased PC filters did not react
       with SO2.
   19.  NaCI and NH NO3 particles im-
       pacted on a silicone-oiled PC fil-
       ter  did not  react to a significant
       extent  with HNO3 or SO2, re-
       spectively.
   20.  Acidic  NaHSO4  particles  im-
       pacted on a silicone-greased PC
       filter reacted to a limited extent
       (1.7 to 3.5%) with NH3.
   21.  In a 24-hour field test employing
       four  collocated  sampling sys-
       tems incorporating the  modified
        impactors,  the concentrations of
        coarse-particle nitrate-N and sul-
       fate were determined to be 0.939
        ±0.032 ug/m3 (±3.4%) and 0.222
        ± 0.007 ng/m3 (±  3.3%), respec-
        tively.  However, substantial per-
        centages of the nitrate, sul-
        fate, and ammonium (36%, 44%,
        and 50%, respectively)  were col-
        lected on  the  bent-tube  inlets
        rather than the  impaction disks.

Recommendations
    1.   Impaction surfaces  used to
        sample particles (or to prevent
        their entry into downstream de-
        nuders and filter packs) should
        be coated with a  suitable oil or

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    grease to  prevent bounce.   At
    high mass loadings, excess oil
    should be used.
2.   If an oiled porous glass disk is
    used to collect particles for sub-
    sequent chemical analysis,  the
    analyst should make sure that
    the extraction procedure used to
    remove the particles from  the
    disk is adequate.
3.  The nature of the nitrate and
    sulfate collected on the impactor
    inlet during collection  of field
    samples should be investigated,
    and experiments should be con-
    ducted  to  ascertain  whether
    jarge particles deposited in the
    inlet will react to a  significant
    extent with HNO3, SO.,, NH3, or
    other gaseous pollutants.
4.  A small vane system able to turn
    a  bent-tube inlet  mounted on a
    rotary union and orient it into the
    wind should be developed and
    field tested.
5.  The efficiency with which both
    anions and cations  associated
    with various types of particles can
    be  extracted  from  oils and
    greases  into water  should  be
    thoroughly examined and docu-
    mented.
6.  The procedure proposed herein
    for gravimetric determination  of
    large particles should be perfected
    and field tested.
7.  The reactivity of gases (not only
    HNO   SO  and NH,, but  also
    O3,  NO,  NO,,, PAN,  and espe-
    cially SO3) with oils and greases,
    with various types of  Teflon and
    Teflon coatings, with various
    types of  particles (especially
    acidic and basic  particles) col-
    lected on oiled and greased sur-
    faces, and with denuders  and
    their coatings should be explored
    in much more detail. The effects
    of temperature and relative hu-
    midity  on such  reactions also
    need to be thoroughly  examined.
8.  Additional field tests should be
    conducted to determine the pre-
    cision of the  procedure under a
    variety of ambient conditions and
    to explore ways to improve the
    precision and to simplify the pro-
    cedure for use by individuals with
    minimal experience.
9.  Research should continue toward
    the development of a sampling
    system capable of quantitatively
    sampling very large (i.e., 15-20
    u.m) particles.

10. The sampling system herein de-
    scribed should be thoroughly ex-
    amined vis-a-vis its potential use
    in sampling acid aerosols. Par-
    ticular attention should be given
    to:  interactions between gases
    and impacted particles; proce-
    dures for quantifying the acidity
    or basicity of impacted particles;
    and loss or alteration of submi-
    cron particles as they pass
    through the denuders.

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 SJ. Randtke, D.D. Lane, and T. E. Baxter are with the University of Kansas,
    Lawrence, KS 66045.
 Russell Wiener Is the EPA Project Officer (see below).
 The complete-report, entitled "Development of a Sampling Procedure for Large
   Nitrogen- and Sulfur-Bearing Aerosols," (Order No. PB90-235 789/AS; Cost:
   $23.00 cost  subject to change) will be available only from:
         National Technical Information Service
         5285 Port Royal Road
         Springfield, VA 22161
         Telephone: 703-487-4650
 The EPA Project Off her can be contacted at:
         Atmospheric Research and Exposure Assessment Laboratory
         U.S. Environmental Protection Agency
         Research Triangle Park, NC 27711
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati, OH 45268
  Official Business
  Penalty for Private Use $300

  EPA/600/S3-90/048
                                                                                                                       .

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