United States
Environmental Protection
Agency
Atmospheric Research and
Exposure Assessment Laboratory
Research Triangle Park NC 2771 1
/ 1 \
Research and Development
EPA/600/S3-89/058 Sept. 1989
v-xEPA Project Summary
Determination of C2 to C12
Ambient Air Hydrocarbons in
39 U.S. Cities, from
1984 Through 1986
Robert L. Seila, William A. Lonneman, and Sarah A. Meeks
Currently more than 60 urban areas
are not in compliance with the Na-
tional Ambient Air Quality Standard
(NAAQS) for ozone. The use of pho-
tochemical models will be necessary
to forecast nonmethane organic com-
pound (NMOC) reductions needed to
attain the NAAQS. These models
require knowledge of the individual
organic species in ambient air. To
this end, speciated hydrocarbons
were determined in over 800 ambient
air samples obtained from 39 U.S.
cities during 1984 through 1986.
Whole-air samples were collected in
electropolished, stainless steel
spheres on week days from 6 a.m. to
9 a.m. during June through Septem-
ber each year. Two gas chromato-
graphic (GC) procedures with cryo-
genic sample preconcentration were
employed to separate and measure
C2 to C12 hydrocarbon species. One,
a packed silica-gel column, measured
C2 hydrocarbon species, while the
second, a 60m x 0.32mm i.d. fused
silica capillary column coated with a
1pm thick liquid phase, separated C2
to C12 species. Menu-driven software
was developed to transfer GC data to
a personal computer. The GC
retention time identification table
shows 314 uniquely numbered peaks,
97 of which are specifically named,
214 are Identified by type (olefin,
paraffin, or aromatic) and 3 are
unknown. The 48 compounds seen in
highest concentration consisted of
25 paraffins, 15 aromatics, 7 olefins,
and acetylene. Sample concentra-
tions of the 64 most abundant
species are reported.
This Project Summary was devel-
oped by EPA's Atmospheric Research
and Exposure Assessment Laboratory,
Research Triangle 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 ozone forming potential of an air
mass is strongly dependent on the ratio
of nonmethane organic compounds
(NMOC) to nitrogen oxides (NOX). Reduc-
tion of this ratio by reducing NMOC
emissions is believed to be the most ef-
fective means for reducing ozone levels
in urban areas. Local pollution control
agencies use photochemical computer
models to estimate the NMOC reductions
needed to achieve acceptable ozone con-
centrations. One of these models, the
Empirical Kinetic Modeling Approach
(EKMA), requires the input of local am-
bient NMOC and NOX concentrations in
order to achieve precise results. There-
fore, accurate measurements of ambient
NMOC concentrations are clearly vital to
the determination of NMOC reduction
estimates.
Currently in the U.S., more than 60
urban areas are not in compliance with
the NAAQS for ozone (Federal Register,
1983). In I984, the EPA Office of Air
Quality Planning and Standards (OAQPS)
began an assistance program designed
to determine NMOC in participating non-
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attainment cities using the new PDFID
method. As part of this project, the
Atmospheric Research and Exposure
Assessment Laboratory (AREAL) of the
EPA analyzed over 800 samples from 39
cities from 1984 through 1986 to de-
termine the speciated hydrocarbon
composition.
Experimental Methods
Sampling
Integrated whole-air samples were col-
lected during weekdays from 6 to 9 a.m.
from June through September of 1984
through 1986. Samples were pumped
into evacuated, electropolished stainless
steel spheres, and air-freighted to
Research Triangle Park, where a
contractor gave them identification
numbers and analyzed them by the
PDFID method. The AREAL analyzed
about 15 percent of the samples to de-
termine the detailed hydrocarbon con-
centrations. Table 1 lists the cities
sampled with the corresponding number
of samples by year.
Analysis
Two GC analyses were employed to
determine the presence of C2 to C12 hy-
drocarbons, because one column could
not provide adequate separation of the C2
hydrocarbons (ethane, ethylene, acety-
lene). These latter compounds were
separated on a packed silica-gel column.
C2 to C12 hydrocarbons were separated
on a 60 m x 0.32 mm i.d. fused silica-
capillary column coated with a 1 nm thick
coating of a cross-linked, non-polar liquid
phase (DB-1, J&W Scientific, Rancho
Cordova, CA). Both analyses employed
the cryogenic preconcentration of about
500 ml of air prior to injection and flame
ionization detection. Hydrocarbons were
identified by retention time and quantified
by their FID response relative to a
National Institute of Standards and
Technology (NIST) propane-in-air
standard reference material (SRM).
Data Reduction
The large amount of data-800 samples
with 120 to 240 peaks per sample-
necessitated the use of a computerized
data management system. Menu-driven
software was developed for a personal
computer (PC) to provide sample tracking
and management, data acquisition from
the HP-5880A GC, and report generation
functions. Data were transferred bidirec-
tionally between the GC and a PC via
RS-232 interfaces and cable at 1200
bits/s.
Results and Discussion
The limits of detection (LOD) and
quantification (LOQ) were 0.04 and 0.12
ppb as carbon (ppbC), respectively.
These values are a function of the
sample amount injected onto the column;
however, they remain constant for all GC
peaks regardless of retention time. We
used an 8.22 ppmC propane-in-air SRM
from the NIST for calibration. A response
factor was determined using response
data from several SRM analyses each
year at the beginning of the study. The
same response factor was used
throughout the study for all compounds.
The overall variation for the 1984 through
1986 period was ±12 percent. The
coefficient of variation (C.V.) of the initial
analyses used to determine the 1985 re-
sponse factor was 1.75 percent, while the
C.V. over the entire 1985 study was 3.68
percent, demonstrating that the inter-day
variation was a little more than twice the
intra-day variation.
The quantitative precision was deter-
mined by calculating individual peak C.V.
for the 12, 1984 duplicate determinations.
Concentration variability decreased (i.e.,
precision increased) as concentration
increased. The concentration variability
was typically less than 10 percent for
concentrations greater than 9 ppbC. The
C.V. for concentrations between 2 and 9
ppbC ranged up to 30 percent and up to
95 percent for concentrations less than 2
ppbC. No relationship was observed
between concentration precision and
retention time, which indicated that quan-
titative precision was the same for all
peaks.
Retention time identifications were de-
termined by a combination of the follow-
ing: (1) Analysis of known hydrocarbons
prepared by syringe injection into Tedlar
bags filled with air. (2) Reference to the
chromatography literature retention times.
(3) Comparison to retention time results
of other investigators. (4) Pre-column
strippers to remove olefins and olefins
plus aromatics from ambient samples.
This latter approach was useful for both
the confirmation of identified peaks and
the determination of unidentified peaks as
paraffin, olefin, or aromatic.
The accuracy of the method depends
upon the peaks being properly identified.
The HP-5880A GC names peaks accord-
ing to a user-created calibration table of
retention times, unique calibration nun
bers for each peak, and an optional pes
name. A retention index system based c
user-identified reference peaks correc
for shifting retention times. A match
obtained if the corrected retention tim
falls within a calibration table retentic
window that consists of each retentic
time plus or minus user-specifie
tolerance percentages. Our experienc
was that this method for naming peat
worked well. A GC calibration table we
prepared that identified 314 peaks by
calibration number. The table consiste
of 97 peaks specifically named, 21
identified by carbon number and bon
type (olefin, paraffin, or aromatic), and
labeled unknown.
Since retention times are used for ider
tifying peaks, it follows that retention tim
precision is important. The standard d<
viations for the 113 most frequently ot
served peaks were determined an
plotted versus the mean retention time
Retention time standard deviation as
function of the retention time was n<
constant. At a retention time of 11.5 mil
the standard deviation rose abruptly froi
0.015 min to 0.11 min and then gradual
declined to 0.03 min at a retention time <
28 min. We believe this effect is due 1
water condensation at -50°C.
The quality of stainless steel canistei
as storage containers for C2 to C
hydrocarbons was tested. Six ambiei
samples were stored after initial analysi
re-analyzed once after one week, and r<
analyzed three consecutive times at tr
end of a second week. The results ii
dicated that the entire range of C2 to C
hydrocarbons determined by the methc
presented herein was unaffected b
stainless steel canister storage for up 1
two weeks.
A statistical summary of the concentr.
tion results for the 48 most abundai
peaks for all samples from 1984 throug
1986 is shown in Table 2. The table lis
compounds in descending order of abui
dance with their corresponding concei
tration range statistics, which are numtw
of samples (n), median concentration
ppbC, minimum concentration (min
twenty-fifth and seventy-fifth percent!
concentrations (25% and 75%), an
maximum concentration (max). The 4
compounds consisted of 25 paraffins, 1
aromatics, 7 olefins, and acetylene. Thrc
of the aromatics were not specifical
identified. The report presents tables
concentrations by site of the 64 mo
abundant hydrocarbons.
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Table 1. Cities Where NMOC Samples
EPA Region City
1 Boston, MA
Portland, ME
II New Haven, CT
Bridgeport, CT
Bronx, NY
Manhattan, NY
Trenton, NJ
III Baltimore, MD
Scranton, PA
Philadelphia, PA"
Washington, DC
Richmond, VA
IV Atlanta, GA
Birmingham, AL
Charlotte, NC
Chattanooga, TN
Memphis, TN
Miami, FL
West Palm Beach, FL
V Akron, OH
Cincinnati, OH
Cleveland, OH
Indianapolis, IN
Chicago, IL"
VI Beaumont, TX
Clute, TX
Dallas, TX
El Paso, TX
Fort Worth, TX
Houston, TX"
Texas City, TX
West Orange, TX
Baton Rouge, LA
Lake Charles, LA
Tulsa, OK
VII Kansas City, MO
St. Louis, MO
Denver, CO"
Salt Lake City, t/r
Were Collected
1984
_
—
_
—
—
—
—
_
9
7
10
10
7
6
16
12
8
3
8
10
7
—
10
—
9
10
13
8
13
—
13
16
—
—
—
11
—
—
—
Number of Samples
1985
8
13
_
—
—
—
—
—
24
11
14
—
—
—
—
—
—
—
17
—
—
T9
17
23
17
19
22
15
16
16
16
18
18
_
—
7986
_
—
76
76
76
72
76
7
—
74
77
~
14
13
—
—
—
—
—
_
—
—
—
22
13
~
14
9
16
26
—
—
—
—
12
^_
—
25
27
"City had two sites.
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Table 2. Concentration" Statistics for Most Abundant Compounds
Compound N Median Min.
25%
75%
Max.
Isopentane
n-Butane
Toluene
Propane
Ethane
n-Pentane
Ethylene
m&p-Xytene
2-Methylpentane
Isobutane
Acetylene
Benzene
n-Hexane. 2-Ethyl-1 -Butene
3-Methylpentane
1 ,2,4-Trimethylbenzene
Propylene
2-Methylhexane
o-Xylene
2,2,4-Trimethylpentane
Methylcyclopentane
3-Methylhexane
2 -Methyl propene, Butene-1
Ethylbenzene
m-Ethyltoluene
n-Heptane
2, 3-Dimethylbutane
c-2~Pentene
1 ,2,3-Trimethylbenzene
Methylcyclohexane
n-Decane
1,3, 5-Trimethylbenzene
C11 Aromatic
\-2-Pentene
o-Ethyltoluene
p-Ethyltoluene
C10 Aromatic
n-Octane
2-Methyl-l -Butene
1 ,2-Dimethyl-3-Ethylbenzene
\-2-Butene
2,3,4-Tnmethylpentane
2-Methylheptane
1 ,4-Diethylbenzene
3-Methylheptane
n-Nonane
Cyclohexane
2,4-Dimethytpentane
Cyclopentane
832
833
836
835
830
834
707
836
836
835-
709
835
836
831
828
835
763
831
835
834
828
827
836
832
831
834
750
758
836
835
825
773
807
836
831
832
799
822
756
811
833
820
821
832
821
817
827
823
45.3
40.3
33.8
23.5
23.3
22.0
21.4
18.1
14.9
14.8
12.9
12.6
11.0
10.7
10.6
7.7
7.3
7.2
6.8
6.4
5.9
5.9
5.9
5.3
4.7
3.8
3.6
3.4
3.4
3.3
3.0
3.0
2.9
2.9
2.8
2.8
2.6
2.6
2.5
2.5
2.5
2.5
2.4
2.2
2.2
2.2
2.2
2.1
1.4
4.5
2.7
1.8
0.6
1.0
1.2
1.3
1.2
1.4
*w
1.0
0.8
0.1
••
0.4
0.2
0.9
0.4
0.5
0.3
••
0.7
0.1
0.1
0.3
••
0.1
0.3
0.2
0.3
0.2
0.1
0.2
0.1
0.2
0.2
0.1
0.2
0.1
0.1
0.1
0.1
0.1
0.2
0.2
0.2
0.1
26.2
23.9
20.6
12.2
12.4
12.5
13.2
11.3
8.5
8.4
7.3
7.9
6.2
6.4
6.7
4.3
4.5
4.7
3.9
3.7
3.5
3.8
3.6
3.3
2.8
2.3
1.9
1.6
2.0
1.9
2.0
1.8
1.5
1.9
1.8
1.8
1.6
1.4
1.6
1.4
1.5
1.3
1.5
1.4
1.3
1.1
1.3
1.2
71.6
65.5
56.6
45.2
41.0
36.0
35.8
30.0
23.5
28.6
23.2
19.9
18.4
16.6
17.1
14.3
11.7
11.6
11.6
10.3
9.7
9.8
9.8
8.6
8.2
6.1
6.0
5.7
6.0
6.0
5.1
4.7
4.7
4.6
4.7
4.5
4.6
4.4
4.3
4.2
4.4
4.2
4.0
3.9
4.2
4.8
3.8
3.2
3393
5448
1299
393
470
1450
1001
338
647
1433
114
273
601
351
81
455
173
79
106
293
168
365
159
83
233
177
339
1701
184
138
51
71
291
54
54
235
163
242
149
337
78
75
33
109
89
409
72
104
" All concentrations are parts-per-billion as carbon.
** Concentrations below the limit of quantification (0.1 ppbC).
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The EPA authors, Robert L Seila (also the EPA Project Officer, see below),
William A. Lonneman, and Sarah A. Meeks, are with the Atmospheric Research
and Exposure Assessment Laboratory, Research Triangle Park, NC 27711.
The complete report, entitled "Determination of C2 to C72 Ambient Air
Hydrocarbons in 39 U.S. Cities, from 1984 Through 1986," (Order No. PB 89-214
1421 AS; Cost: $42.95, 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:
Atmospheric Research and Exposure Assessment Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
United States Center for Environmental Research
Environmental Protection Information
Agency Cincinnati OH 45268
Official Business
Penalty for Private Use $300
EPA/600/S3-89/058
MIiCT
Sa«"5.;«
CHICAGO
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