Ecological Research Series
      COLLECTION OF  SULFUR  GASES
WITH  CHEMICALLY-TREATED FILTERS
                  Environmental Sciences Research Laboratory
                       Office of Research and Development
                       U.S. Environmental Protection Agency
                 Research Triangle Park, North Carolina 27711

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                RESEARCH REPORTING SERIES

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

      1.  Environmental  Health Effects Research
      2.  Environmental  Protection Technology
      3.  Ecological Research
      4.  Environmental  Monitoring
      5.  Socioeconomic Environmental Studies
      6.  Scientific and Technical Assessment Reports (STAR)
      7.  Interagency Energy-Environment Research and Development
      8.  "Special" Reports
      9.  Miscellaneous Reports

This report has been assigned to the ECOLOGICAL RESEARCH series. This series
describes research on the effects of pollution on humans, plant and animal spe-
cies, and materials. Problems  are assessed for their long- and short-term influ-
ences. Investigations include formation, transport, and pathway studies to deter-
mine the fate of pollutants and their effects. This work provides the technical basis
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aquatic, terrestrial, and atmospheric environments.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.

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                                             EPA-600/3-78-041
                                             April  1978
      COLLECTION  OF SULFUR GASES WITH
         CHEMICALLY-TREATED FILTERS
                     by
     George R. Namie, Robert F. Reardon,
    Norbert Schmidt and Lester L. Spiller
 Atmospheric Chemistry and Physics Division
 Environmental Sciences Research Laboratory
    U.S. Environmental Protection Agency
Research Triangle Park, North Carolina  27711
 ENVIRONMENTAL SCIENCES RESEARCH LABORATORY
     OFFICE OF RESEARCH AND DEVELOPMENT
    U.S. ENVIRONMENTAL PROTECTION AGENCY
RESEARCH TRIANGLE PARK, NORTH CAROLINA  27711

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                                 DISCLAIMER

     This report has been reviewed by the Environmental Sciences Research
Laboratory, U.S. Environmental Protection Agency, and approved for publica-
tion.  Mention of trade names or commercial products does not constitute
endorsement or recommendation for use.
                                     ii

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                                  ABSTRACT

     Chemically treated membrane filters were tested for use in collection
and measurement of hydrogen sulfide and sulfur dioxide.  Four chemical
treatments were tested.  Silver nitrate and silver nitrate-tartaric acid
filters were used for collection of hydrogen sulfide, and lithium hydroxide
and potassium bicarbonate were used for collection of sulfur dioxide.
Sampling was performed using a tandem filter holder so that the test gas
would pass through each filter in sequence.  There was a pre-filter whose
function was to remove the aerosol component.
     For collection of hydrogen sulfide the silver nitrate filters had an
efficiency of 84% when used with a flow rate of 1.0 liter/minute, and for
collection of sulfur dioxide the lithium hydroxide filters had an efficiency
of 85% at 1.0 liter/minute.  It was found that the silver nitrate filters
began to absorb sulfur dioxide after several days, so the test gas should
pass through the lithium hydroxide treated filter prior to the silver
nitrate treated filter.
                                     iii

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                                 CONTENTS

Abstract	ill
Figures and Tables	   vi
     1.   Introduction 	    1
     2.   Conclusions  	    2
     3.   Experimental Procedures  	    3
     4.   Results and Discussion	   11
References	   21
                                     v

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                                  FIGURES

Number                                                           Page
  1  Laboratory sampling unit	   4
  2  Three element filter holder 	 	   6
  3  Vacuum source 	  10
                                  TABLES
  1  Efficiencies of AgNCL Treated Filters (Expected Sulfur
       Density-1.12 yg/cm2)  	  11
  2  Efficiencies of LiOH Treated Filters (Expected Sulfur
       Density-0.62 yg/cm2)	12
  3  Saturation Limits for Each Filter Type	13
  4  Interferences from Other Organic Sulfur Compounds on
       Each Filter Type	  14
                                     VI.

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                                  SECTION 1
                                INTRODUCTION

     A principle source of atmospheric sulfur may be from sulfate reduction
by anaerobic bacteria (1,2).  One of the significant products of the reduc-
tion may be hydrogen sulfide, which could be oxidized and contribute to the
atmospheric sulfate loading.
     A simple, inexpensive method is needed to measure simultaneously long-
time averages of hydrogen sulfide (H-S), sulfur dioxide (S0~), and aerosol
concentrations.  Treated filters offer a method of measuring wide variations
of these concentrations, since the flowrate through the filter can be
adjusted to yield a collected sample within the sensitivity limits of the
analysis method.  A tandem filter setup was chosen to prevent contamination
of the SO- and H-S adsorbing filters with particulate sulfur.
     Sampling of H_S and SO. has been described by Adams (3), Pate et al (A),
and Natusch (5) and Huygen (7).  Collection methods similar to that dis-
cussed here have been described by Ensinger (6) and Lewin et al (9).

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                                  SECTION 2
                                 CONCLUSIONS

     Lithium hydroxide (LiOH) and potassium bicarbonate (KHCO,,) treated
filters were compared for their ability to collect S02>  The LiOH treated
filter was found to be better since its collection efficiency remained
unchanged for periods of up to a month, and the KHCO, treated filters lost
efficiency and selectivity after one day.  The efficiency of the LiOH
treated filters dropped sharply at humidities less than 30%.
     Silver nitrate (AgNO,) and silver nitrate-tartaric acid (AgNO,-tartaric
acid) treated filters were used to collect HS.  Their efficiencies were
shown to be dependent on humidity.
     A flow rate of 1.0 liter/minute appeared to be best for short sampling
times and high efficiency.  The best filter sequence was found to be; (1)
Teflon prefilter, (2) LiOH treated filter, and (3) AgNO~ treated filter.
Under these conditions efficiencies of about 84% and 85% can be expected
from the AgNO, and LiOH filters for H^S and S02, respectively, when analyzed
by X-ray fluorescence.

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                                  SECTION 3
                           EXPERIMENTAL PROCEDURES

GENERATION OF TEST GAS
     In Figure 1 is shown the system used to test the chemically treated
filters.  The test gas consisted of zero air (less than 1 ppm hydrocarbon),
humidified zero air, and one or more sulfur containing gases (given off by
a permeation tube).  All of the elements of the test gas were combined and
the total flow, humidity, and temperature were determined.
     For the compounds tested, a permeation tube in a constant temperature
bath was used to generate the test mixture.  The permeation tube was housed
in a glass or Teflon chamber in series with metal heat-transfer coils.  The
temperature bath was regulated to within + 0.1C.  (For almost all test runs
the temperature bath was set at 20  0.1C.)
     Zero grade air was further cleansed by passing the air through activated
charcoal and a drying agent.  The flow was adjusted using a needle value and
a Brooks rotometer (Model I355-OOAIIAAA).  Before being run through the test
filters, additional zero air and/or humidified zero air was often added to
the test gas mixture to adjust the humidity and total flow rate.  The
humidity of the test gas was then measured by an EG&G Model 880 dewpoint
hygrometer.  Teflon tubing and stainless steel connectors were used to
minimize any reactivity of the test gases with the laboratory apparatus.
MEASUREMENT OF TEST GAS CONCENTRATION
     After the test gas mixture had stabilized, its concentration was
measured with a Meloy model SA-160-2 sulfur gas analyzer.  The analyzer was
previously calibrated using known sulfur containing gas concentrations.
     The sulfur analyzer output voltage was displayed on a digital voltmeter
(DVM), which was recorded after the voltage transients due to concentration

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           II
           ix
           II
    SULFUR GAS
     SAMPLE
                                        OUTLET
            I    TEST
            FILTER HOLDER
                  !"WET" DILUTION AIR
      DRY DILUTION AIR
CONSTANT!
 PERMEATION
    TUBE
HEAT TRANSFER
i     COIL
       TWO STAGE
   PRESSURE REGULATOR
                                      HUMIDIFIER      'CONSTANT
i                                                     TEMPERATURE
                                                     BATH
                                                                          J
                      SHUT-OFF VALVE
                    (gH
       ZERO GRADE
       AIR CYLINDER
                                                  ROTAMETERS
                                     IMETERING VALVES
                                      ACTIVATED
                                      CHARCOAL
                                      'FILTER
                  Figure 1.   Laboratory sampling unit.

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fluctuations disappeared.  After recording the voltage, the analyzer was dis-
connected from the test gas line and the filter holder was placed in series
between the test gas generator and the sulfur gas analyzer.  The analyzer
measured the sulfur gas concentration of the test gas that passed through
the filter, and readings were recorded a few minutes before the end of the
test run.  Test runs usually lasted 60 minutes.  If the analyzer's output
voltage for the filter run was the same as the voltage for the lab air, it
was assumed that the filter collected 100% of the sulfur gas.
FILTER HOLDERS
     In Figure 2 is shown the three-element filter holder.  The filter holder
consists of a modified Millipore single filter holder No. XX-50-04700, which
has been elongated and is fitted with three stainless steel discs to separate
the three filter elements.  Teflon or Vitron rings are used to seal the filter
elements in the holder.
     This tandem filter holder was developed to prevent the filters from
touching.  It was found that filters which touched produced erroneous results.
FILTER PREPARATION
     A number of cellulose  filter types were tested, and  the Millipore
WSWP04700 filter paper was  chosen because of its combination of strength,
thinness, and surface structure.
     This inexpensive filter was treated  in chemical solutions to make
selective collectors for  the various volatile  sulfur compounds found in the
atmosphere.  The two sulfur compounds of  primary interest were SO-  and HS.
Adams  (3), Pate el  al  (4),  Natusch and Hinygen (5)  listed many different
chemical solutions  that  absorb  SO- and H-S.  Several of  these solutions
were chosen and tested.   For S09, lithium hydroxide  (LiOH)  and potassium
bicarbonate  (KHCO-) were tested.  For H-S,  silver  nitrate (AgNO-) described
by Ensinger  (6) and silver  nitrate-tartaric acid  (AgNO_-tartaric  acid) were
 tested.
                                     7 
                                       5

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                                                               COUNTER BORE
                                                              1/32 in.-BOTH SIDES
                                                                ALL SPACERS,
     1-6/1 io.

Ml/18 in.    1/Vta.--*^
                                                                                 2 SLOTS -1/16 i. DEEP  110 APART
                                                                                    EACH SPACER WIDTH EQU.
                                                                                     ROLLER DIA +0.005 in.
                 OUTER SLEEVE
                         Figure 2.   Three  element  filter  holder,

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 S02 FILTER-LiOH SOLUTION
     Solution:
     36g LiOH
     20 ml 9% triton-x-305
     30 ml propylene glycol
     dilute to 1000 ml with deionized water
     pH 11.63
     Blank Millipore WSWP04700 filters were treated as follows:  The filters
were soaked in the solution for 6-7 minutes.  After soaking, the filters were
placed on a glass plate and the excess solution was carefully squeezed out by
rolling with a glass test tube.  The filters were then dried by hanging in
ambient air for at least one hour (the room must be low in volatile sulfur
compounds and of low or moderate humidity).  After drying the filters were
stored in Millipore petrislides at ambient temperature until used.
S02 FILTER-KHC03 SOLUTION
     Solution;
     lOg KHCO-
     7.5 ml glycerine
     dilute to 50 ml with deionized water
     pH 8.34
     In preparing filters treated with KHCO_, a special problem was encoun-
tered.  The KHCO_ is reduced easily to form a compound which is not selec-
tively reactive with SO-.  To achieve the best possible results several
methods of filter preparation were used, and the resulting filters were
tested.
     The methods are as follows:
     1.   A 0.2 ml aliquot of the solution was applied to the center of the
          filter and was allowed to spread evenly throughout the filter.
     2.   A 1.0 ml drop of solution was deposited in the center of the filter
          and was allowed to spread evenly through the filter.
     3.   A pump sprayer was used to deposit 3.0 ml of solution evenly on the
          filter.

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     4.   The filter was dipped into the solution for 1 second, removed and
          allowed to dry for 1 hour.
     Method #3 had the best efficiency for the collection of SO,, and showed
the longest lifetime.  It was adopted as the method of production for KHCO.
filters.
 H.2S FILTER-AgNCL SOLUTION
     Solution;
     15g AgN03
     25 ml propylene glycol
     dilute to 290 ml with deionized water
     pH 3.12
     Filter preparation for the AgNO~ soaked filters was exactly the same as
for LiOH soaked filters, except that the filters were soaked for 20 minutes
in the solution.  These filters must be stored in darkness until used.
H2S  FILTER-AgNO^rTARTARIC ACID SOLUTION
     Solution;
     2g AgN03
     4.5g tartaric acid
     3 ml propylene glycol
     dilute to 100 ml with deionized water
     pH 2.0
     Blank WSWP04700 filters were treated as follows:  The filters were
soaked in solution for 30 seconds, placed between two Gelman type AE high
volume filters, and dried in a oven at 75C for 1 hour.  After drying, the
filters were placed in individual Millipore petrislides and stored in
darkness at ambient temperature,
TEST PROCEDURES
     The filter was removed from the petrislide using tweezers and positioned
in the filter holder, so that the chemically treated side of the filter faces
the incoming air flow.  The type of filter holder used, single or tandem, is
dependent on the type of test to be done.  Some of the tests involved using
a prefilter, S0_, and H_S filters, while others were carried out on only one

                                      8

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filter.  Some of the different tests had variables such as flow rate, humidity,
temperature, wetting of the prefilter, and filters in contact with each other.
FIELD WORK
     During field tests, a central location was established.  At this
location the loading of the filter holders was carried out and all record
keeping was done.
     The order of the filters was established to be an aerosol prefilter, and
S02 filter, and an H-S filter.  The S02 filter was made from the LiOH solution
and the H~S filter was made from the AgNCL solution.
     A complete monitoring station consisted of a three element filter
holder and a vacuum source.
DESCRIPTION OF VACUUM SOURCE
     The Vacuum source (Figure 3) is a Cast #1531 vane type 0.1 hp vacuum
pump mounted in a metal box.  An aluminum bracket is attached to one end of
the box and a control valve and two female bulkheads terminated by hose
connectors are mounted on the bracket.  The vacuum pump is cooled during
operation by a ventilation fan.  The complete assembly weights 8.6 kg. (19
Ibs.) and draws 1.5 amperes from a 115 volt power line.
     To maintain constant flow, a Millipore critical orifice (1 liter/
minute) is screwed into the outlet of the filter holder.  The outlet part
of the filter holder is connected to the hose connectors of the vacuum
source with 6.3 mm (0.25 in.) rubber tubing.  If only one holder is used,
one of the hose connectors must be capped.
     To operate correctly, the vacuum at the critical orifice must be greater
than the critical vacuum specified.   (Beyond the critical vacuum, flow
through the orifice will be constant.)  The control valve in the box allows
the pump to be loaded past critical vacuum while providing enough air to
prevent pump overheating.
FILTER ANALYSIS
     At the end of the test run or field run the filters were returned to
the petrislides and submitted for analysis.  The two methods of analysis
                                     r,
                                      o

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FLOW
                                                       /. ORIFICES v
                                                  A
    DASHED LINE
:  SURROUNDS MAJOR
COMPONENTS MOUNTED
    IN TOOL BOX
                                           ROTAMETERSCONNECTED AS
                                           !   DURING ADJUSTMENT
                           Figure 3.  Vacuum source.
                                      10

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used were:  (1) an energy-dispersive X-ray fluorescence analyzer  for  sulfur
density at the surface of the filter and  (2) liquid ion chromatography  for
sulfate.
                                      i-
                                      11

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                                  SECTION 4
                           RESULTS AND DISCUSSION

PREFILTER
     An untreated 47 mm filter is used in front of the selectively reactive
filters to collect the aerosol content of the sample gas.  It is important
that the prefilter be unreactive to the sulfur containing gases in the
sample and that it not restrict flow.  The prefilter also creates turbu-
lence and insures an even distribution of sample on the selectively reactive
filters following the prefilter.  The first experiments were carried out
using a Millipore WSWP04700 as the prefilter.  However, pH measurements on
these filters revealed that it is slightly alkaline.  It is possible that
the acidic H?S may be adsorbed in small amounts by this prefilter and that
a better choice of prefilters could be made.
     Testing showed that the Millipore FALP04700, a Teflon filter (1.0 ym
pore size) was very close to being neutral.  This filter caused no notice-
able restriction of flow in our field setup, yet gave a more even distri-
bution of sample on the succeeding sulfur gas filters.
FILTER TEST RESULTS
     The collection efficiency in SC/SEX100%, where SE is the amount of
sulfur containing gas molecules entering the filter and SC is the amount
collected.  SE is controlled using a permeation tube of known permeation
rate.  The efficiency of HS and SO., collection was found to be a function
of both humidity and flow rate for the AgNO  and LiOH filters.  In all of
the cases sited below, XRF was used to determine the efficiencies.  The
Meloy sulfur gas analyzer indicated 100% efficiency during all of these
runs.  The efficiencies of less than 100% were attributed to adsorption
beneath the surface of the filter.  Most likely, the difference in effi-
ciencies measured by the Meloy sulfur analyzer and by XRF was not due to a
                                    i
                                     12

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loss of adsorbed sulfur by the filter, since repeated analysis of the
filters gave nearly identical results.
FLOW RATES
     The efficiencies of the AgNO,, and LiOH filters were  tested over a
range of 0.5-2.0 liter/minute.  The results of these runs are given in
Tables 1 and 2.  For AgNO., filters run using a prefilter  the flows of 0.5
liter/minute and 1.0 liter/minute gave mean efficiencies  of 84.6%  (std.
dev. = 5.55) and 84.3%  (std. dev. = 6.52) respectively.   The LiOH filters
run with a prefilter showed an optimum flow rate of 1.0 liter/minute with
an efficiency of 84.6%  (std. dev. = 4.13).
HUMIDITY
     At each of the flow rates the relative humidity of the test gas was
varied from 10% to 100% (when possible).  The results of  these runs are
given in Tables 1 and 2.  As noted before the LiOH filters at 1 liter/minute
had a mean efficiency of 84.6% (std. dev. = 4.13) and the AgNO~ at the same
flow rate had an efficiency of 84.3% (std. dev. = 6.52).  It was noted that
the efficiency of the LiOH dropped sharply at relative humidities less than
39% which has been reported in the past by Lewin and Zacheu-Christensen  (9)
when using alkaline impregnated filters to collect S0.
TEMPERATURE
     A cursory test of  temperature effects on the treated filter efficiency
was carried out.  No efficiency changes were noted in the range of 10-30C
for both LiOH and AgNO^
SATURATION TIMES
     The Meloy sulfur analyzer with a strip chart recorder was used to
monitor relative efficiencies of the filters over long periods of time.
The four types of treated filters were run over night to  determine the
saturation limit of each.  The saturation limits are given in Table 3 where
the time is the duration that the filter exhibited 100% efficiency.  For
samples of this magnitude X-ray fluorescence cannot be used since  there  is
a great deal of sample  penetration.  This was shown by doing XRF on the
exposed filters on both sides.  Nearly equal quantities of sulfur were

                                     13

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TABLE 1.  EFFICIENCIES OF AgN03 TREATED FILTERS
          (EXPECTED SULFUR DENSITY-1.12 yg/cm2)
Flow
(1/min)
0.5

1.0

1.5

2.0



2
S detected, yg/cm :
Efficiency, %:
2
S detected, yg/cm :
Efficiency, %:
2
S detected, yg/cm :
Efficiency, %:
2
S detected, yg/cm :
Efficiency, %:
Relative Humidity
10%


0.90
80
0.92
83
0.92
82
20%
0.95
85
0.88
78
0.82
73
0.83
74
30%
1.00
89
0.90
80
0.94
84
0.98
88
40%
0.93
83
0.90
80
1.02
91
0.83
74
50%
1.05
94
1.01
90
1.00
89
0.92
82
60%
1.00
89
1.10
98
0.96
86
0.92
82
70%
0.95
85
0.91
81
0.95
85
0.84
75
80%
0.90
80
0.98
88
0.84
75
0.92
82
90%
0.90
80
0.94
84




100%
0.85
76






Efficiency
Mean
84.6

84.3

83.1

79.9

Std. Dev.
5.55

6.52

6.31

5.03


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                               TABLE 2.  EFFICIENCIES OF LiOH TREATED FILTERS
                                         (EXPECTED SULFUR DENSITY-0.62 yg/cm2)










Flow
(1/min)
0.5

1.0

1.5

2.0



2
S detected, yg/cm :
Efficiency, %:
2
S detected, yg/cm :
Efficiency, %:
2
S detected, yg/cm :
Efficiency, %:
2
S detected, yg/cm :
Efficiency, %:
Relative Humidity
10%
0.13
21
0.30
48
0.14
22
0.13
21
20%
0.35
56
0.50
81
0.09
14
0.17
27
30%
0.40
65
0.52
84
0.22
35
0.15
24
40%
0.43
69
0.53
85
0.45
73
0.20
32
50%
0.42
68
0.51
82
0.43
70
0.28
45
60%
0.45
73
0.55
89
0.45
73
0.28
45
70%
0.44
71
0.53
85
0.46
74
0.29
47
80%
0.45
73
0.55
89
0.39
63
0.32
52
90%
0.44
71
0.55
89
0.46
74


100%
0.47
76
0.48
77




Efficiency
Mean
69.1

84.6

71.0

47.2

Std. Dev.
5.86

4.13

4.20

3.30

Ln

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found on each side of the exposed filters.  Ion chromatograph would be a
preferable measure of exposures of this intensity.

             TABLE 3.  SATURATION LIMITS FOR EACH FILTER TYPE
Filter type
Sulfur gas
Time (hours)
Concentration
(PPB)
LiOH
so2
4.5
119

KHC03
so2
7.0
119

AgN03
H2S
24
63

AgN03/
tartaric acid
H2S
18
63

SELECTIVITY
     All four treated filter types are 100% selective to their respective
sulfur gases when they are freshly made.  That is, KHCO_ and LiOH treated
filters do adsorb H-S and AgNO- and AgNO- tartaric  acid treated filters do
not adsorb SO-.  However only the LiOH filter has a selectivity lifetime
greater than one month.  The AgNO- filter begins to pick up small amounts
of S02 after approximately 2 days.  The KHCO- treated filters will pick up
both H_S and SO- after they are a day old, unless they are refrigerated.
Tests of selectivity lifetime have not been performed on the AgNO--tartaric
acid treated filters, but is appears to be very much the same as for AgNO-.
Because of the eventual loss of selectivity in the AgNO  filters, it was
decided that the test gas flow should go through the prefilter first, then
the LiOH filter, with the AgNO- filter being last.
     Other sulfur compounds were used to further test the selectivity of
the LiOH and AgNO- filters.  The results of these tests are summarized in
Table 4.
                                     16

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             TABLE 4.  INTERFERENCES FROM OTHER ORGANIC SULFUR
                       COMPOUNDS ON EACH FILTER TYPE
GAS
H2S
SO,
CH3SH
(CH3)2S
(CH3)2S2
cs
COS
FILTER TYPE
LiOH
N
G
N
N
N
N
N
AgN03
G
N
N
N
N
N
N
                         G = Good Collection
                         N = No Collection  .
DETECTION TECHNIQUES
     The Meloy sulfur gas analyzer (model SA-160-2) served as a good in situ
guide to the effectiveness of the filter being exposed.  Using the pre-
determined calibration curve, the concentration of the test gas (S09 or
H2S) could be determined both before and after passing through the filter.
     Filter analysis was done by two means.  X-ray fluorescence, described
by Lorenzen (6), was used the majority of the time.  A newer technique, ion
chromatography using the Dionex Model 14 ion chromatograph, is presently
being examined.
     The X-ray fluorescence method (XRF) measures only surface deposition.
This was found not to be a limitation except for exposures when a signifi-
cant amount of sample was adsorbed beneath the surface of the filter.  The
center-weighted reading of the XRF posed some problems since the deposition
on the filter was also center-weighted.  The results of the XRF were con-
sistent enough, however, that this could be taken into account when
                                     17

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calculating concentration.  Advantages of  the XRF are  that  analysis  can be
done relatively quickly and it  leaves the  filter intact  for further  tests.
     The  ion chromatograph  (1C) has  the advantage that it can measure  the
total sulfur present with no  concern for the distribution of deposition.
However,  the results from the 1C  to  date have been  too inconsistent  to make
any quantitative statements on  the method.
MINIMUM DETECTION LIMIT
     The  concentration of sample  is  related to the  density  of sulfur
detected  using the equation:
                                                                     9
     Concentration, ppb = volume  of  sulfur containing  molecules x  10
                                     volume of air

                        = isL x (24.6 1/g mole air)  (10~6 g/yg) (109)
                                      (34.08 g S/g  mole  S)
where D is the sulfur detected by X-ray fluorescence and has the units
     2
yg/cm , E is the fractional collection efficiency,  F is  the sample volu-
metric flow rate in liters/min, t is the sampling time in minutes, and A  is
the area  of collection.  The  quantity 24.6 1/g mole is the  molar volume of
an ideal  gas at 25C and 1 atm.  This equation holds for a  sample  con-
taining 1 atom sulfur per molecule.  The fractional collection efficiencies
for AgNCL and LiOH filters were approximately 0.865, flow rate is  usually
        -*                                                            2
1.0 1/min, and the minimum detectable density by X-ray is 0.05 yg/cm .  The
                                    2
actual area of the filter is  8.04 cm .  Reducing the above  equation, the
minimum detectable concentration becomes simply a function  of sample time:
                                   335
     Minimum concentration (ppb) =  where t is in minutes.

               Sample Time         Minimum Concentration
                (minutes)                  (ppb)
                    30                       11.17
                    60                        5.58
                   120                        2.79
                   240                        1.40
                   360                        0.93
                   720                        0.46
                                    18

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DEPOSITION OF SAMPLE
     It was desired to have the sample deposited only at the surface of the
filter so that accurate analysis could be accomplished using X-ray fluo-
rescence.  With the particulate filters there was no apparent adsorption of
the sample below the filter surface for any of the filter types tested.
For the selectively reactive filters no penetration was found for exposures
corresponding to roughly 50% of the saturation limit.  It was also found
that for sampling rates greater than 2.0 liters/minute that some penetration
was found for LiOH.
     Due to the design of the filter holders, the deposition of sample on
the filter was not radially uniform.  The local velocity of the sample gas
at the edge of the filter was lower than the local velocity at the center
of the filter.  The resulting "center-weighted" deposition was analyzed
using an X-ray beam which looks mainly at the center of the filter.  This
gave readings higher than the actual average surface density of the sample.
It was reasoned that as long as the surface deposition distribution had the
same shape for each run, that the results would be consistent.  No effi-
ciencies of 100% or greater have been seen in the laboratory tests using a
profilter so the "center-weighted problem" should not be resulting in any
exaggerated field measurements.
     X-ray analysis had continually indicated that the selective filters
run without particulate were more efficient than those run with particu-
lates.  Yet, tests on the prefilters indicated that  they were not adsorbing
the sample.  In reality, the presence of the prefilter increased the
turbulence behind it.  By increasing the turbulence, the velocity of the
center of all successive filters was more nearly equal the velocity at the
edge, i.e. the deposition was less "center-weighted."  The density of the
filters run with prefilters would then appear to be  less than those run
without them.
     The deposition on the particulate filter is center-weighted and there
is no way to modify this without redesigning the filter holder.  However,
it is felt from comparisons of  readings from alternative aerosol measuring
                                     19

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devices that the accuracy of the X-ray technique on particulates run in
these holders is very good.
WETTING
     Tests were run to determine the consequence of a WSWP prefilter
becoming wet during a normal run.  One drop of deionized water was placed
on the prefilter and it was exposed to a sulfur gas.  Wet prefliters picked
up about 0.11 yg of SCL.  No adsorption of H^S by the wet prefilter was
indicated by XKF.
                                    20

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                                 REFERENCES
1.   Rasmussen, R.A.  Emission of Biogenic Hydrogen Sulfide.  Tellus, XXVI,
     1-2:254-260, 1974.

2.   Hitchcock, D.R.  Biogenic Sulfur Sources- and Air Quality in. the United
     States.  NSF-RANN Grant No. AEN-7514571, National Science Foundation,
     Washington, D.C.  20050.

3.   Adams, D.F.  Analysis of Sulfur Containing Gases in the Ambient Air
     Using Selective Prefilters and a Microcauometric Detector.  APCA
     Journal, Vol. 18:  145-148, March, 1968.

4.   Pate, J.B., J.P. Lodge, and M.P. Neary.  The Use of Impregnated Filters
     to Collect Traces of Gases in the Atmosphere.  Anal. Chim. Acta.,
     28:  341-348, 1963.

5.   Natusch, D.F., etc.  Determination of Hydrogen Sulfide in Air-An
     Assessment of Impregnated Paper Tape Methods.  Anal. Chem. Vol. 46:
     410-415, 1976.

6.   Ensinger, R.S.  Atmospheric Hydrogen Sulfide Measurement Using a
     Silver Nitrate-Based Tape Sampler.  General Motors Research Report,
     EV-19, June 15, 1975.

7.   Huygen, C.  The Sampling of Sulfur Dioxide in Air with Impregnated
     Filter Paper.  Anal. Chim. Acta., 28:349-360, 1963.

8.   Lorenzen, J.A.  Environmental Monitoring Device for X-ray Determination
     of Atmospheric Chlorine, Reactive Sulfur, and Sulfur Dioxide.  Interna-
     tional Business Machines Corporation Technical Report, E80-E101,
     February 5, 1975.

9.   Lewin, E. and B.  Zachau-Christensen.  Efficiency of 0.5N KOH Impregnated
     Filters for S07 Collection.  Atmospheric Environment, Vol 11:861-862,
     1977.
                                     21

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                                   TECHNICAL REPORT DATA
                            (Please read Instructions on the reverse before completing)
1. REPORT NO.
  EPA-600/3-78-041
                             2.
                                                           3. RECIPIENT'S ACCESSION>NO.
4. TITLE AND SUBTITLE
  COLLECTION OF  SULFUR GASES WITH
  CHEMICALLY-TREATED FILTERS
             5. REPORT DATE
               April 1978
             6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
  George R. Namie,  Robert F. Reardon,
  Norbert Schmidt  and Lester L. Spiller
                                                           8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
             10. PROGRAM ELEMENT NO.
               1AA603
     (Same as Box  12)
                                                           11. CONTRACT/GRANT NO.
12. SPONSORING AGENCY NAME AND ADDRESS
  Environmental Sciences Research  Laboratory - RTF, NC
  Office  of  Research and Development
  U.S. Environmental Protection Agency
  Research Triangle Park, North Carolina  27711
             13. TYPE OF REPORT AND PERIOD COVERED
               In-house    FY 77
             14. SPONSORING AGENCY CODE

               EPA/600/09
15. SUPPLEMENTARY NOTES
16. ABSTRACT
        Chemically treated membrane filters were evaluated to collect hydrogen
   sulfide and sulfur dioxide.   Four chemical treatments were tested.  Silver
   nitrate and silver nitrate-tartaric acid filters were used to collect hydrogen
   sulfide, and lithium hydroxide and potassium bicarbonate were used to collect
   sulfur dioxide.  Sampling was performed using a tandem filter holder so that
   the  test gas would pass through each filter in sequence.  A pre-filter  was
   used to remove the aerosol  component.

        For collecting hydrogen sulfide, the silver nitrate filters had an
   efficiency of 84% when used with a flow rate of 1.0 liter/minute; for
   collecting sulfur dioxide,  the lithium hydroxide filters had an efficiency of
   85%  at 1.0 liter/minute.   It was found that the silver nitrate filters  began to
   absorb sulfur dioxide after several days; thus, the test gas should pass through
   the  lithium hydroxide treated filter prior to the  silver nitrate treated filter.
17.
                                KEY WORDS AND DOCUMENT ANALYSIS
                  DESCRIPTORS
                                              b.lDENTIFIERS/OPEN ENDED TERMS
                             COS AT I Field/Group
   *Air pollution
   *Sulfur dioxide
   *Hydrogen sulfide
   *Aerosols
   *Measurement
   *Filter materials
                              13B
                              07B
                              07D
                              13K
18. DISTRIBUTION STATEMENT

   RELEASE TO PUBLIC
19. SECURITY CLASS (ThisReport)
   UNCLASSIFIED
21. NO. OF PAGES
  28
                                              20. SECURITY CLASS (Thispage)
                                                 UNCLASSIFIED
                                                                         22. PRICE
EPA Form 2220-1 (9-73)
                                             22

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