United States
Environmental Protection
Agency
Environmental Sciences Research
Laboratory
Research Triangle Park NC 27711
s~
(
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Research and Development
EPA-600/S2-80-194 Apr 1981
Project Summary
GC/MS Analysis of
Ambient Aerosols in the
Houston, Texas, Area
Catherine H. Skintik
This study was designed to provide
information on the organic aerosol
pollutants in the Houston, Texas, area.
The Research Triangle Institute (RTI)
was responsible for qualitative and
quantitative analysis of ambient air
aerosols and vapor samples collected
in the Houston area by the Radian
Corporation of Austin, Texas. Three
different types of samplers were used:
high volume (hi-vol) and dichotomous
samplers were employed to collect
particulates, and resin-trap samplers
(developed at the Illinois Institute of
Technology Research Institute and
known as IITRI samplers) were em-
ployed to collect vapor-phase organic
samples. Filters and sorbent resins
were shipped to RTI following field
sampling. A total of 23 samples were
analyzed: 12 filter and adsorbent trap
samples, 5 dichotomous samples, and
6 hi-vol samples.
Hi-vol samples were extracted and
solvent-partitioned prior to analysis by
glass capillary gas chromatography/
massspectrometry (GC/MS). Dichot-
omous filters were extracted and the
concentrated extracts analyzed directly
by GC/MS. Vapors were analyzed by
thermal desorption from the resin bed
followed by GC/MS.
Analyses showed the presence of
many saturated and unsaturated ma-
terials in all samples. The extracts
from hi-vol filters contained small
quantities of organics, and their anal-
ysis was complicated by the presence
of background contaminants tenta-
tively identified as siloxanes. Results
from the dichotomous samples indi-
cated insufficient collection of ma-
terial for comprehensive air analysis.
Vapor-phase organics collected in
IITRI samples consisted predominantly
of hydrocarbons, alkylated benzenes,
and some chlorinated compounds.
Quantitative analysis was carried out
for selected components from each
sample type.
This Project Summary was devel-
oped by EPA's Environmental Sciences
Research Laboratory, Research Tri-
angle Park, NC, to announce 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
The 1977 Clean Air Act Amendments
called for EPA research studies in the
Gulf Coast area. Priority was given to
the problems of aerosol pollutants, and
Houston, Texas, was chosen as the
initial study site. The EPA issued a
procurement request to obtain gas
chromatography/mass spectrometry
(GC/MS) evidence on the identity of the
organic particulate pollutants present in
the atmosphere above Houston and
surrounding areas. The evidence ob-
tained was intended to guide studies of
health effects from ambient aerosols
and to determine sources and causes of
aerosol pollution in the Houston area.
-------
Sampling
The major sampling effort for the
Houston air study was provided by
Radian Corporation, Austin, Texas,
under a separate contract. All samples
analyzed by RTI were collected by
Radian during September and October
1978 using filter and adsorbent trap,
dichotomous, or hi-vol samplers.
Filter and Adsorbent Trap
(IITRI) Sampler
The filter and adsorbent trap sampler
consisted of a conventional high-volume
sampler modified to allow for sampling
of vapor-phase material downstream of
the aerosol filter. The vapors were
collected by passing a portion of the
post-filter airstream through cartridges
containing a trapping medium consisting
of polymeric sorbents. Two sorbent-
containing cartridges were connected
in series, and four such cartridge pairs
comprised the vapor sampling unit. This
sampler was designed and constructed
by researchers at the Illinois Institute of
Technology Research Institute (IITRI)
and is referred to in this report as the
IITRI sampler. A total of three IITRI
samplers (12 cartridge pairs) was used
for this program.
The sorbent selected for use in the
samplers was Tenax® GC, a phenylene
oxide polymer with well-tested vapor
trapping properties.
All sorbed organic species had to be
removed from the Tenax® GC before it
was released for field use. These ma-
terials were removed by thermal de-
sorption, after which the levels of back-
ground materials remaining were as-
sessed by glass capillary gas chroma-
tography /flame ionization detect ion
(GC/FID) of the desorbed vapors.
Once the cartridge pairs were cleaned
by thermal desorption, all U-tubes were
reassembled and each sealed sampler
was shipped to Houston. The samplers
were designated by number (samplers
1, 2, and 3), and each of the four
cartridge pairs for each sampler was
numbered 1 through 4. In addition, the
individual sorbent beds were labeled as
either upstream (U) or downstream (D).
Thus, each sample could be described
by a single designation preceded by "IT"
for IITRI. For example, the upstream
Tenax® GC sample from U-tube 3,
sampler 1, was referred to as IT1-3U.
All sampling information was recorded
on data sheets supplied by RTI to Radian
and returned with each sampler. This
information is detailed in Table 1. One
cartridge pair for each sampler was
utilized as a field blank. The blank was
never exposed to the sampling stream,
but experienced the same shipment,
storage, and handling conditions as the
sample cartridges.
Dichotomous Sampler
The dichotomous sampling effort for
the Houston study was carried out by
the EPA (Inorganic Pollutant Analysis
Branch, Atmospheric Chemistry and
Physics Division). A portion of the many
dichotomous filters used for aerosol
collection was shipped to RTI as specified
in the sampling protocol. Five "fine"
filters were designated for extraction
and analysis by RTI. The sampling
information for the dichotomous sam-
ples is shown in Table 2.
Hi-Vol Sampler
The high-volume samples were col-
lected on quartz fiber filters (Gelman
Micro Quartz). Prior to field studies,
investigations were conducted to deter-
mine the extent of background organics
contained in the quartz fiber filters
(OFF). Each filter was subjected to
solvent washing experiments to deter-
mine the results of such clean-up
procedures and the best wash medium
if clean-up was shown to be effective.
Filter extracts and solvent washes were
analyzed using packed column GC/FID.
Results showed that both methanol/
chloroform and diethyl ether removed
significant amounts of contaminants
but that methanol/chloroform was
more efficacious than ether. A variation
in contaminant levels for filters from the
Table 1. Samp/ing Data—IITRI Samples
IITRI
Sample No.
IT1-1 (blank)
171-2
IT1-3
IT1-4
IT2-1 (blank)
IT2-2
IT2-3
IT2-4
IT3-1
IT3-2
IT3-3
IT3-4 (blank)
Houston
Site
#21-Alief
U23-Stude Park
#23-Stude Park
—
#23-Stude Park-
Central
#23-Stude Park-
Central
#21 -A lief -West
#22-Baytown Area-
North
#22-Baytown Area-
North
#22-Baytown Area-
North
—
Sampling
Data
—
10-08-78
(day}
J 0-06 -78
(day)
10-06-78
(night)
—
10-11-78
(day)
10-11-78
(night)
10-10-78
(day)
10-10-78
(day)
10-11-78
(night)
10-11-78
(day)
—
Sampling
Rate (t/m/nj
—
2.84
2.84
2.84
—
2.84
2.84
2.84
2.84
2.84
2.84
—
Sampling
Time (min)
—
710
720
595
—
585
720
720
690
660
720
—
Sample
Volume (L)
—
2,0/6
2,045
1,690
—
1,661
2,045
2,045
1,960
1,874
2.045
—
-------
Table 2. Sampling Data—Dichotomous Samples.
Dichotomous Houston Sampling Sampling Sampling Sampling
Filter No. Site Date Rate (l/min) Time (hr) Volume (m3)
4F-011
4F-012
4F-018
4F-021
4F-022
#19
#19
#17
#21
#21
9-27-78
(night)
9-28-78
(day)
10-6-78
(day)
10-9-78
(day)
10-10-78
(day)
16.7
16.7
16.7
16.7
16.7
12.0
12.0
11.8
12.0
12.0
12.0
12.0
11.8
12.0
12.0
same lot was noted, and these results
were conveyed to Radian prior to field
sampling.
Data sheets were supplied to Radian
for recording pertinent sampling in-
formation and were returned to RTI.
Sample Analysis
To minimize problems associated
with sample decomposition, all ana-
lytical work was carried out in a labora-
tory fitted with yellow lights (trans-
mission >500 nm); samples and sample
extracts were never allowed to exceed
50°C, and were stored under conditions
of refrigeration and darkness.
IITRI Samples
The Tenax® GC was removed from
the IITRI samplers, and a measured
portion of the resin was transferred to
clean glass cartridges. The cartridge
contents were then analyzed by glass
capillary GC/MS. The whole sample
was introduced to the analytical system
by thermal desorption into a cryogenic
capillary trap and then rapidly swept
onto the chromatographic column. Each
cartridge was loaded with a known
amount of perfluorobenzene and per-
fluorotoluene for use in quantitation.
Qualitative data interpretation was
done by visual inspection of the spectra
and comparison with standard reference
spectra. Quantitation was achieved by
determining the peak intensity of a
characteristic mass for a compound
from the chromatographic peak. The
amount of compound in the sample was
Ithen calculated using the relative molar
response (RMR) factor and the integrated
area for a standard. The concentration
in ambient air was calculated using the
volume sampled.
Dichotomous Samples
Preliminary Experiments
The dichotomous sampler was de-
signed to collect aerosols for size frac-
tionation, mass determination, and
compositional characterization. The
sample rate (16.7 l/min) is low com-
pared to the commonly used hi-vol
sampler (—600 l/min), and thus the
amount of aerosol collected is smaller.
Since organics typically comprise 5 to
15 percent of the total mass of air
aerosols, and since only a limited fraction
of a sample extract can be introduced
into the GC/MS system, experiments
were undertaken prior to field sample
analysis to optimize the organics recov-
ery procedure. Efforts were directed
toward reducing the extracts to the
smallest practical volume, since the
maximum aliquot that could be removed
for GC/MS injection was fixed at ap-
proximately 1 fj\. Given the small a-
mounts of organics likely to be present
and the size of the containers available
for use, concentrations of an extract to
low /j\ volumes without concomitant,
significant losses of sample components
presented some difficulty.
Information obtained from EPA led to
examination of Schenk-Bauer sedimen-
tation tubes as appropriate containers
for sample concentration. Recoveries
were tested using 14C-7, 12-dimethyl-
benz(a)anthracene, a compound pre-
sumably representative of an important
class of aerosol organics. The tests
succeeded in concentrating a significant
amount of material in a small volume of
solvent, from which aliquots could then
be removed for GC/MS analysis. Varia-
tions in the precise extent of recovery
could be compensated through the use
of internally added standards.
Analysis of Field Samples
Based on the preceding study, final
concentration of dichotomous filter
extracts was achieved using Schenk-
Bauer sedimentation tubes. Each di-
chotomous filter was extracted using a
custom-made Teflon® extraction block
provided by EPA. Two extractions were
carried out with approximately 4 ml of
chloroform and sonication in a water
bath. The extracts were combined and
the internal standard (anthracene-dio)
added. The extract was then transferred
in portions to the sedimentation tubes
for solvent removal. Just prior to GC/MS
analysis, the dried extracts were recon-
stituted in 10//I of chloroform. Approxi-
mately 1 //I was removed for injection
onto the GC column.
Hi-Vol Samples
Extraction/Partition
Hi-vol filters (OFF) were extracted
overnight with methanol using a Soxhlet
apparatus. Following solvent removal,
the residue was fractionated. The indi-
vidual fractions were then concentrated
for GC/MS/COMP analysis.
The efficacy of the scheme was as-
sessed by subjecting a mixture contain-
ing known amounts of compounds to
the partition procedure. The mixture
consisted of benzoic acid, phenol, quin-
oline, hexadecane, phenanthrene, and
ethylene glycol. These compounds were
chosen to represent the five classes of
materials produced by the partition
scheme (all these materials have been
found in air paniculate samples except
ethylene glycol). No information on the
composition of the polar neutral fraction
was available; therefore, ethylene glycol
was included as a likely component of
this fraction based on its known chemi-
cal properties. The experiment was
conducted using both large and small
mass samples. Recoveries were deter-
mined gravimetrically.
As a further check on the procedure,
thin-layer chromatography (TLC) scans
were conducted on each fraction to
ascertain the extent, if any, of compound
spillover into other fractions. No such
spillover was detected.
-------
GC/MS/COMP Analysis
Samples were analyzed using an LKB
2091 GC/MS with a dedicated PDP-
11/34 data system. The samples were
chromatographed on an OV-101 capil-
lary column (25 m, WCOT, obtained
from LKB). The column was held at
100°Cfor2 minutes after injection, and
then heated to 265°C at a rate of 8°/min.
Carrier gas flow rate was 1.8 ml/min.
Injector temperature was 245°C. Mass
spectral scans were taken every 3 sec,
scanning from 5 to 492 amu. The ion
source temperature was 210°; electron
energy, 70 eV; trap current, 50 //A;
accelerating voltage, 3500 V; and multi-
plier setting, 400-500. Total ion current
and mass spectra plots were generated
for interpretation.
Data were interpreted by comparison
of the unknown spectra with standard
reference collections. Where no refer-
ence spectrum was available, or where
spectral quality was not sufficient for
positive identification, the compounds
were labeled "tentative." Further vali-
dation of equivocal identification was
made by consultation with other chem-
ists and spectroscopists experienced in
similar research. This mass spectral
interpretation protocol was established
to extract the maximum information
from the data and to guard against
misidentification. The specific compound
identification criteria are as follows: (1)
computer interpretation, (2) manual
interpretation, (3) manual interpretation
plus retention time/boiling point of
compound, (4) manual interpretation
plus retention time of authentic com-
pounds, and (5) criterion number (4)
plus independent confirmation tech-
niques.
Results
Within the limits of the GC/MS
technique, complete identifications of
the organics isolated from each sampler
medium were made. Of the compounds
identified, certain components were
selected for quantitation. The selection
was based on relative abundance and
the known hazard potential of each
compound, and was made after consul-
tation with the project officer. The
results for each of the three sample
types are discussed individually in the
following sections.
IITRI Samples
Five quartz fiber filters were returned
for analysis of aerosol organics (a blank
filter was subsequently made available
for analysis), and 12 sorbent-containing
cartridge pairs (9 samples, 3 blanks)
were returned for analysis of volatiles.
Volatiles—Qualitative Analysis
The 12 IITRI cartridge tubes contained
an upstream and a downstream Tenax®
GC bed (~2.5 g Tenax® GC/cartridge)
thus providing 24 samples for analysis.
Analyses of both the upstream and
downstream cartridges for all blanks
and for two sample cartridges were
carried out. For all these samples it was
evident that the analysis of the down-
stream cartridge represented a duplica-
tion of effort since a large number of
compounds (>50) were found on both
the upstream and downstream cartridge,
the same compounds were found on the
downstream as the upstream cartridge,
and no useful information was obtained
by virtue of analysis of the downstream
'cartridge. Therefore, only the upstream
cartridge was analyzed for the bulk of
the volatile samples. A summary of
those samples analyzed is provided in
Table 3. For each sample a gas chro-
matogram, in the form of a total ion
current (TIC) plot (TIC versus mas!
spectral scan number) was obtained
Each peak of theTIC plot was numbered
and the identification of all compound;
corresponding to each peak was tabulated
A large number of compounds was
identified for each cartridge. With on<
exception, from 104 to 174 compounds
were characterized for each upstrearr
cartridge, with approximately two-
thirds of these components detected or
the corresponding downstream cartridge
The appearance of relatively large
numbers of components on the down-
stream cartridge indicates significam
breakthrough from the upstream car-
tridge. In view of the volume of aii
sampled (Table 1), and the known break-
through volumes for similar components
using Tenax® GC under similar condi-
tions, these findings are not surprising
The vast bulk of volatile species (—80 tc
85 percent) was identified as saturated/
monounsaturated hydrocarbonsand
alkylated aromatic hydrocarbons. For
the amount of Tenax® GC used and the
temperatures at which sampling was
carried out, the breakthrough volumes
for these compound types are on the
Table 3. Summary of Analysis of IITRI Volatiles
Qualitative Analysis
IITRI Sample No. * by GC/MS
Number of Components
Identified
IT1-1U (Blank)
IT 1-1D (Blank)
IT1-2U
IT1-2D
IT1-3U
IT1-3D
IT1-4U
IT1-4D
IT2-1U (Blank)
IT2-2D (Blank)
IT2-2U
IT2-2D
IT2-3U
IT2-3D
IT2-4U
IT2-4D
IT3-1U
IT3-1D
IT3-2U
IT3-2D
IT3-3U
IT3-3D
IT3-4U (Blank)
IT3-4D (Blank)
82
46
174
112
147
104
167
89
69
165
153
149
68
104
107
81
70
*Sample Code: IT3-4U refers to IITRI Sampler #3, cartridge pair #4, upstream cartridge*
^-Indicates analysis performed. \
-Indicates analysis not performed.
-------
order of 0 to 100 I and 100 to 1,000 I,
respectively. The amount of air sampled
for the IITRI cartridges averages about
2,000 I.
The qualitative data from the IITRI
cartridge analysis shows a considerable
number and amount (from TIC) of com-
pounds associated with the blank car-
tridges. These cartridges were never
intentionally exposed to ambient air,
and thus should have produced gas
chromatographic patterns similar to
those for components desorbed from
the IITRI cartridges. The intensity of the
chromatographic pattern obtained for
the blanks indicates exposure of these
cartridges to ambient air. This was
presumably due to leakage through
either the toggle valves controlling air
flow to the IITRI U-tubes or the Swage-
lock fittings.
The qualitative profile of the volatile
components collected by the IITRI sam-
plers is very similar to results obtained
by other workers at various urban sites.
Approximately 150 compounds were
identified from each cartridge. Of these
about 60 percent were saturated/
monounsaturated hydrocarbons, about
20 to 25 percent were aromatics, about
5 percent were halogenated hydrocar-
bons, and the remaining components
(~10 to 15 percent) consisted of oxygen-
ated compounds (aldehydes, ketones,
ethers).
Sampling for vapor phase material
was carried out at three sites represent-
ing a suburban community, a downtown
area, and a heavily industrialized site.
Based solely on the qualitative results,
no major trends or characteristics
regarding site specificity were noted.
Although similar volumes of air were
sampled at each site, the average
number of compounds identified from
the industrialized site was less (93) than
the average number identified from the
suburban site (162) or the downtown
area (158). While this observation may
seem noteworthy, the limited number of
samples analyzed from each site and
the excessive volume of air sampled for
the amount of Tenax® GC used detract
from its significance.
No significant differences were noted
between results obtained for samples
collected during the day and those
collected at night.
Volatiles—Quantitative Analysis
The selection of compounds for quan-
titative determination was based on
considerations of relative abundance
and toxicity. These criteria were adopted
following consultation with the project
officer. Toxicity information was ob-
tained from the "Handbook of Environ-
mental Data on Organic Chemicals."
Using the method of relative molar
response (RMR) factors, reference quan-
titation standards were obtained and
their GC/MS response relative to an
internal standard was determined under
the same conditions as were used for
the analysis of field samples. In some
cases, duplication of effort was avoided
by the determination of RMRs for several
similar species using a single, represen-
tative standard. It is known from past
experience that structurally similar
compounds generally produce similar
response factors.
A total mass of each species was
divided by the volume of air sampled to
provide ambient air concentrations.
These quantitation results are shown in
Table 4. In one case, methylene chloride,
the large amount of material introduced
Table 4. Quantitation Results from IITRI Volatiles Analysis
Compound
Concentration (ng/m3)
IT1-2U IT1-3U IT1-4U IT2-2U IT2-3U IT2-4U IT3-1U IT3-2U IT3-3U
n-Hexane
methylcyclohexane
n-heptane
5920
1582
998
126
4115
788
n- octane
n-nonane
n-decane
n-undecane
n-dodecane
n-tridecane
benzene
toluene
ethylbenzene
xylene isomer
xylene isomer
1 ,2,3-trimethylbenzene
1 ,2,4- trimethylbenzene
1 , 3, 5 - 1 rimet h ylb enzen e
ethyltoluene isomer
styrene
naphthalene
chloroform
carbon tetrachloride
methylene chloride
1 ,2-dichloroethane
trichloroethylene
1, 1 , 1 -trichloroethane
dichlorobenzene
1059
1086
1418 1796
2495 2478
880 811
6636
2860 10443
3835
1659 1362
333
234 233
473
181
165
7169
4142 3624
4211
6049
4285
11214
8126
8064
1151
1383
1253
1650
8971
27817
4561
9631
9201
33454
3112
23698
21841
7763
2240
756
4078
79281
1052
1209
1963
14197
8239
1725
371
1480
13451
3172
2476
5336
20124
4781
337
4107
766
208
677
169982
6786
179
158
1319
429
104
685
388
149526
219
2543
79
203
3393
6242
1458
2475
643
721
1922
284218
1967
216
1169
99
47
5
22
64
22
236
15200
1414
15
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Table 5. Summary of Qualitative Results from Dichotomous Filter Extracts
Composition of Real Components
Filter
No.
4F-011
4F-012
4F-018
4F-021
4F-022
Total
Peaks
Identified
25
41
42
28
25
Background
Components
10
16
16
13
8
Real
Components
15
25
26
15
17
Sat'd
Hydrocarbons
8
13
11
6
12
Unsat'd
Hydrocarbons
2
5
8
3
1
Alkyl
Phenols
1
1
2
1
1
Unknowns
4
6
5
5
3
to the GC/MS produced analyzer satu-
ration. For this compound a minimum
concentration is therefore reported.
However, as noted previously, the rela-
tively large volume of air sampled
exceeded the known breakthrough
volumes (BTVs) for most components.
Thus all quantitative results must be
interpreted as minimum concentrations.
Nonvolatiles
Since each IITRI sampler was used in
conjunction with a hi-vol sampler, a
quartz fiber filter (OFF) corresponding to
each of the IITRI cartridge pairs was
used at each sampling period. Five such
filters were returned to the RTI for
aerosol organics analysis.
The analytical protocol for nonvolatile,
aerosol organics involved Soxhlet ex-
traction followed by fractionation of the
extracted organics into five major frac-
tions. These fractions were individually
analyzed using GC/MS. Earlier results
obtained for the analysis of the hi-vol
filters not used in conjunction with the
IITRI samplers showed very low levels of
organics in each of the five fractions.
Consequently, for all but one of the hi-
vol filters used with the IITRI samplers,
the fractionation scheme was not em-
ployed, and the GFF extract was analyzed
directly by GC/MS. Diminished peak
intensities from the TIC plots and the
relatively few compounds identified
even from the nonfractionated extracts
seem to indicate that the levels of
nonvolatile aerosol organics from these
samples are quite low. The other obvious
result of these analyses is the presence
of substantial levels of background
components, principally phthalate esters
and siloxanes.
Dichotomous Samples
Preliminary Studies
Prior to complete analysis of aerosol
organics from the five dichotomous
filters, the levels of background contam-
inants and their sources were deter-
mined. Control runs were carried out to
allow for the contribution of background
components from the extraction solvent,
from the dichotomous filter, and from
the extraction device utilized in the
scheme. All operations for the control
runs were identical to those used for the
analysis of field samples.
The results of these control runs
indicated that the number of contami-
nants was acceptably low. Not unex-
pectedly, phthalate esters are present in
the solvent; the only other major con-
taminant is an unsaturated hydrocarbon
(octadecene) extracted from the extrac-
tion block. The relative retention time
and mass spectral fragmentation pat-
terns of all background compounds
were noted for subsequent use during
qualitative analysis of the field samples.
Qualitative Analysis
The number of components identified
from each extract ranged from 25 to 43,
of which a substantial portion was
background contaminants. Phthalate
esters and siloxanes were the major
contaminants. Of those compounds
identified as non-background materials,
saturated and unsaturated hydrocar-
bons accounted for nearly all species.
An alkylated phenol (Cs and/or do) was
also identified in each extract, presum-
ably indicating a motor vehicle exhaust
source for this compound. A summary
of these results is presented in Table 5.
Quantitative Analysis
The amount of aerosol collected on
each dichotomous filter is quite low
(approximately 100 to 2,000 fjg) com-
pared to aerosol collection devices more
commonly used for nonvolatile organics
analysis. Thus, low-level components
were not present in quantities sufficient
for full qualitative/quantitative treat-
ment.
Of the materials characterized from
the dichotomous filter extracts, roughly
half were identified as non-background
components. Of these, 5 to 6 were
present at levels that permitted quanti-
tation. These compounds, all higher
molecular weight long chain hydrocar-
bons plus nonylphenol, are shown in
Table 6.
The variation both qualitatively and
quantitatively between extracts is small,
and no trends were noted regarding
sampling site or time of sampling. The
levels of saturated hydrocarbons (Cis -
CIB) were comparable to levels from
other urban sites and slightly higher
than levels found from nonurban sites. |
Hi-Vol Samples
The quartz fiber filters designated for
analysis under this program were re-
ceived approximately 3 months after
field collection. They were stored and
shipped by Radian Corporation per
protocol and were stored at -20°C in our
laboratories until analysis was initiated.
Although it had been anticipated that a
gravimetric determination of total col-
lected aerosols would be made, tearing
and loss of small but significant portions
of the OFF during unpacking precluded
such determinations. Following extrac-
tion, the total mass of aerosol organics
was determined; the results are shown
in Table 7. The organic loads ranged
from low to average in comparison with
expected levels from urban aerosols.
In contrast to the amount of aerosol
collected by the dichotomous sampler,
the hi-vol sampler is capable of efficiently
trapping approximately 200 to 500
times as much aerosol for a 24-hour
sampling period. It is known from a large
body of work that a wide variety of
organic compounds are adsorbed to th
air particulate. As the direct analysis of
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Table 6.
Quantitative Results from Dichotomous Filter Extracts
Filter
Compound
Cg-alkyl phenol isomer
n-pentadecane
n-hexadecane
n-heptadecane
n-octadecane
octadecene & isomers
4F-001
60 ng( 5.0 ng/m3)
70 ng ( 5.8 ng/m3)
90 ng ( 7.5 ng/m3)
100 ng ( 8.3 ng/m3)
260 ng (21. 7 ng/m3)
4F-012
20 ng ( 1.7 ng/m3)
50 ng 1 4.2 ng/m3)
50 ng ( 4.2 ng/m3)
60 ng ( 5.0 ng/m3)
80 ng ( 6.7 ng/m3/
6620 ng (551.7 ng/m3)
4F-018
20 ng (1.4 ng/m3)
50 ng( 3.6 ng/m3)
100 ng (7.2 ng/m3)
100 ng (7.2 ng/m3)
4F-021
20 ng ( 1.7 ng/m3)
35 ng ( 2.9 ng/m3)
30 ng ( 2.5 ng/m3)
70 ng ( 5.8 ng/m3)
130 ng (10.8 ng/m3)
620 ng (51.6 ng/m3)
Table 7. Total Organics Extracted from Hi-vol Filters
Filter Number Weight of Organics Extracted (mg)
12
13
14
15
65
66
91 (blank)
8.5
5.2
7.3
14.1
23.1
24.3
3.4
such a mixture is not practical owing to
the large number of species present and
the generally unfavorable GC behavior
of some classes (e.g., acids, .bases), a
sample fractionation procedure was
proposed for the organic extracts ob-
tained from the hi-vol filters used in this
study
Qualitative Analysis
Analysis by glass capillary GC/MS
was accomplished for each fraction
from each OFF extract. Firm characteri-
zation proved difficult for all fractions
because of the unexpected presence of
large numbers and amounts of interfering
substances. Coelution of the interfering
species with the compounds of interest
produced complicated MS fragmentation
patterns, obscured sample components
in some cases, and effectively raised
sensitivity limits. The problem was
noted for virtually all hi-vol samples (no
such interferences were seen for the
4ITRI or dichotomous samples), and
investigations into the precise nature of
the substances were made.
The identification of the components
from the sample filters indicated the
presence of a disproportionate number
of phthalate esters and siloxanes of
indeterminate structure. Both classes of
compounds possess single ions that are
characteristic of each compound type. It
is recognized that GC column bleed
from columns employing silicone-based
phases consists predominantly of si-
loxanes. This process is characterized
by a relatively slow increase in GC
baseline and by the continuous presence
throughout a long series of recorded
mass spectra of background levels of
siloxane fragment ions. The siloxanes
found associated with the hi-vol samples
were identified as discrete and, for the
most part, intense peaks, possessing
mass spectra with fragment ion inten-
sities much greater than is normally
observed for column bleed. Thus, in
addition to TIC chromatograms of the
filter blank fractions, single ion plots
(m/z 73,149) were also obtained. When
compared with similar chromatograms
obtained from the GC/MS analysis of a
solvent control, where minimal m/z
73,149 responses were noted, it would
appear that the background components
are associated with the filters utilized
for sample collection. Although each
OFF was cleaned prior to field use, as
noted earlier, a great deal of variation in
background contamination levels was
observed, even for filters from the same
lot. Further, the filter clean-up proce-
dures as carried out in our laboratories
showed that different solvent systems
can be more effective than others for
removing some contaminants. It is
possible that the ether washing proce-
dure used for the hi-vol filters in the
Houston study was not fully efficacious.
Other sources of background contam-
ination were considered, including the
GC septa and silanized glass surface.
Most septa are composed predominantly
of silicone-based polymers. High tem-
perature, exposure to solvent vapor
clouds, and repeated piercing by syringe
needles are among those processes that
could conceivably lead to the production
of siloxanes. Silanized glass surfaces
are commonly used in trace organic
analysis systems, and are therefore also
a likely source of siloxanes. Both mate-
rials were examined and ruled out as
siloxane sources.
From the evidence obtained, within
the limits of funding and effort provided
for this program, the background com-
ponents, principally siloxanes and phthal-
ate esters, appear to be associated with
the QFF used in this study.
Quantitative Analysis
The analysis of extracts from the hi-
vol filters showed generally low levels of
organics, except for the above-men-
tioned phthalate esters and siloxanes.
At the direction of the project officer,
quantitation was carried out only for
saturated hydrocarbons. Based on the
GC/MS behavior of Ci5 - Cia hydrocar-
bon standards, the relative molar re-
sponses (RMRs) of these compounds
were shown to be very similar for m/z
71, 99, and 113 (these ions are present
in all saturated hydrocarbons). Thus
average RMRs for each ion could be
used for the quantitative determination
of each compound possessing these
chromatographic ions. Although any of
the three ions would suffice for quanti-
tation, calculations based on all three
ions were made, where possible, to
detect interference from other com-
pounds, and as a check on the overall
method. To calculate amounts of the
individual compounds, determinations
based on all three ions were averaged. If
one determination was clearly deviant
(i.e., if it differed by more than a factor of
2 from the other values), it was not used
-------
in the calculation of the average. It is
recognized that the use of average
RMRs for all hydrocarbons produces
some uncertainty in final tabulations,
and the figures obtained are best viewed
as approximate. The paucity of material
for filters 0014 and 0065, in part because
of the lower volume of air samples
(approximately 850 m3 as compared to
about 1,050 m3 for filter 0012), allowed
for the quantitation of only five com-
pounds.
For purposes of comparison, concen-
trations of selected aliphatic hydrocar-
bons were obtained from two sources,
one representing results of "clean" air
and the other representing results
obtained from urban air. Average hydro-
carbon concentrations (for the alkanes
chosen) from Houston aerosols are
comparable to other urban levels, and
are significantly higher than values
obtained for "clean" air. It must be
noted that the Houston data presented
here are somewhat suspect because of
the background contamination problem,
the limited number of filters examined,
and the method of estimation utilized.
More rigorous methods of quantitation
are clearly desirable.
Conclusions and
Recommendations
Overall results indicate that the
organic component of Houston ambient
air aerosol is predominantly saturated
hydrocarbons, with lesser but significant
amounts of alkyl aromatics and lower
molecular weight (Ci - C?) halogenated
hydrocarbons. The levels of these mate-
rials are comparable to those found in
other urban atmospheres and are signi-
ficantly higher than those found in
nonurban "clean" air. No clear relation-
ship was observed between levels or
number of components found, and time
or location of sampling site.
The results of this study indicate
several areas where further investiga-
tions could provide useful results.
Specific recommendations include:
1) Modification of the IITRI sampler.
Leakage through fittings and valves
was evident from cartridge analy-
sis; redesign should include vacu-
um tight valves and fittings. The
ease of handling of the sampler
could be improved by construction
of an all-glass or glass/stainless
steel unit.
2) Further research into the use of
the dichotomous sampler for col-
lection and subsequent analysis of
aerosol organics. The automated
nature of this sampler, its high
collection efficiency, sizing capa-
bility, and use of standard Teflon®
filters for collection are attractive
features that could well be taken
advantage of for aerosol organics
analysis. Research should be di-
rected toward improving analytical
sensitivity to a point that is com-
patible with the amount of aerosol
collected by the dichotomous sam-
pler.
3) Investigation of the source and
nature of glass or quartz fiber filter
(GFF and OFF, respectively) back-
ground contamination. The devel-
opment of suitable clean-up-pro-
cedures and a determination of
the precise nature of the contami-
nants associated with such filters
would allow for greater confidence
in analytical results obtained from
samples collected via GFF or OFF.
4) Development of methodology for
accurate nonmethane hydrocarbon
determinations. Software devel-
opment (GC/MS) could provide for
the group quantitation of paraffinic
hydrocarbons as obtained from
the routine analysis of GFF extracts
by glass capillary GC/MS/COMP.
Such data could thus be available
in a reliable and relatively rapid
fashion as an adjunct to compre-
hensive qualitative results from
ambient air aerosol analysis.
This Project Summary was authored by Catherine H. Skintik of WAPORA, Inc.,
Cincinnati, OH 45233.
Kenneth Krost is the EPA Project Officer (see below).
The complete report, entitled "GC/MS Analysis of Ambient Aerosols in the
Houston, Texas, Area," was authored by Charles M. Sparacino of Research
Triangle Institute. Research Triangle Park, NC 27709.
The above report (Order No. PB 81-126 377; Cost: $20.00. 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 Officer can be contacted at:
Environmental Sciences Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
8
i US GOVERNMENT PRINTING OFFICE 1981-757-012/7083
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