United States
Environmental Protection
Agency
Environmental Sciences Research
Laboratory
Research Triangle Park NC 27711
Research and Development
EPA-600/S3-83-026 June 1983
c/EPA Project Summary
Studies of NOx Reactions and 03
Transport in Southern California,
Fall 1976
Chester W. Spicer, Darrell W. Joseph, and Gerald F. Ward
This report describes a four-week
study of oxides-of-nitrogen chemistry
and ozone transport in and around the
southcoast air basin of California The
data base was obtained using three
ground-level monitoring stations and a
twin-engine instrumented aircraft The
ground stations were located approxi-
mately 20, 35, and 50 mi from central
Los Angeles in the prevailing downwind
direction. Measurements were made
at each of these sites from 0900-1700
PST for ozone, nitric oxide, oxides of
nitrogen, nitric acid, peroxyacetylni-
trate, sulfur dioxide, freon-11, nonme-
thane hydrocarbon, carbon monoxide,
methane, ethylene, ethane, nitrate,
sulfate, ammonium, and total nitrogen.
The aircraft made up to three flights
per study day measuring ozone, nitric
oxide, oxides of nitrogen, peroxyace-
tylnitrate, nonmethane hydrocarbon,
methane, carbon monoxide, ethylene,
ethane, freon-11, and temperature. In
all, 42 monitoring flights were con-
ducted over the 22-day study.
The original report summarizes the
results of the study in tables and de-
tailed appendices. Battelle-Columbus
experimenters selected a subset of 11
photochemical ly active days for which
they examined average pollutant pro-
files and air quality trends. The report
discusses the ground-station data in
terms of aerosol nitrogen balance, size
distribution of aerosol constituents,
distribution of oxidized nitrogen, nitro-
gen/sulfur relationships and nitrogen
mass balance. The experimenters chose
specific study days for detailed analy-
sis as case studies, and examined air-
craft and ground data for these days for
evidence of ozone transport oxidized
nitrogen distribution, nitrogen balance,
and oxides-of-nitrogen transformation
rate.
This Project Summary was developed
by EPA's Environmental Sciences Re-
search Laboratory, Research Triangle
Park. NC, to announce key findings of
the research project that is fully doc-
umented in a separate report of the
same title (see Project Report ordering
information at back).
Introduction
The project report presents the results
of a field investigation of atmospheric
transformations of oxides of nitrogen (NOJ
and transport of ozone (03) conducted by
Battelle-Columbus Laboratories under the
sponsorship of the U.S. Environmental
Protection Agency (EPA). The program
focused on reactions and transport in the
urban plume of Los Angeles.
The ambient air reactions of NOX are not
well characterized. Previous characteriza-
tion efforts have focused on developing
analytical methods suitable for studying
such reactions, identifying the major NOX
reaction products, and quantifying the
nitrogen mass balance. Earlier studies in
Los Angeles confirmed smog-chamber
observations that peroxyacetylnitrate (PAN)
and nitric acid (HN03) are the major initial
products of photochemical reactions of
NOX in polluted air. Over a five-week
period in Los Angeles, PAN accounted for
6896 of reacted NOX, HN03 accounted for
1096 and paniculate nitrate (N03~) for
about 396. Approximately 1296 of the
reacted NOX could not be accounted for as
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one of these products. The nitrogen
distribution ratio, FN*, averaged about 7%
at night and 21 % during the day at a site
downwind of Los Angeles. The earlier
study provided the first measurements of
ambient HN03 and the first indication that
HN03 could be present at much higher
concentrations than particulate N03".
Little information on the rate of NOX trans-
formation to products was obtained, al-
though an average pseudo-first-order rate
constant of 0.10 ± 0.05 hr^was con-
sistent with most of the experimental data.
The investigation of NOX reactions sum-
marized here was designed to extend and
validate the earlier results and provide
more information on NOX conversion rales.
The program involved detailed ground-
level and aircraft-monitoring studies as
well as the analysis and interpretation of
the resulting data.
Objectives
The overall objectives of the program
were (1) to determine the distribution of
atmospheric nitrogen compounds and the
relationships among these compounds
and other atmospheric parameters and (2)
to determine the propensity of air masses
to generate and transport 03 over long
distances. Specific objectives of the pro-
ject were:
• To determine the spatial and tem-
poral distribution of oxidized nitrogen
species in the Los Angeles basin,
• To determine the extent to which
measured NOX products can account
for NOX removal from the air (i.e.,
nitrogen mass balance),
• To investigate differences in the
transformation processes for NOX
relative to oxides of sulfur (SOX),
• To estimate the rate of NOX trans-
formation under photochemically re-
active conditions, and
• To investigate the transport of O3
and precursors from urban areas.
Methodology
Field experiments were conducted from
October to November, 1976, in southern
California, and included both ground-level
and airborne monitoring. The experi-
menters utilized three ground stations and
an instrumented twin-engine aircraft for
monitoring. The ground stations were
located approximately 20, 35, and 50 mi
from central Los Angeles in the prevailing
downwind direction, and are shown in
Figure 1 as sites A (Temple City), B
(Upland), and C (Rubidoux). Measure-
ments were made at each of these sites
between 0900 and 1 700 PST for 03,
nitric oxide (NO), NOX, HN03, PAN, sulfur
dioxide (S02), freon-11 (F-11), non-
methane hydrocarbon (NMHC), carbon
monoxide (CO), methane (CH4), ethylene
(C2H2), ethane(C2H4), N03-, sulfate(SO4=),
ammonium (NH4+ ), and total nitrogen.
The aircraft made up to three flights per
day measuring 03, NO, NOX, PAN, NMHC,
CH4, C2H2, C2H4, CO, F-11, and tempera-
ture. In all, 42 monitoring flights were
conducted over 22 days. The data from
the field experiments are contained in
appendices to the report M uch of the data
also appears summarized within the text
of the report itself.
Results and Conclusions
The results of the experimental phase of
the program and the details of the experi-
mental methods are summarized in the
final project report Detailed data are
included in two appendices. Appendix A
lists the daily air quality measurements for
each of the three ground stations. Ap-
pendix B contains flight plans for each
aircraft monitoring mission, together with
maps of 03, NO, and NOX concentrations,
integrated sample collection positions, and
vertical profile sites. Appendix B also in-
cludes the vertical temperature and 03
profiles.
The results of the ground-level and
aircraft monitoring have been interpreted
in terms of N0x-reaction-product distribu-
tion, nitrogen balance, nitrogen/sulfur re-
lationships, NOX transformation rate, and
03 transport Afewofthemoreimportan
study findings are summarized briefly below
During the Los Angeles study, the high
est concentrations of primary pollutant!
generally occurred at the Temple City site
which is closest to the Los Angeles urbat
center. The highest concentrations of 0;
and PAN were measured downwind atthi
intermediate site in Upland, whereas thi
concentration of particulate N03~ wai
greatest at Rubidoux.
Table 1 gives the average daytime distri
bution of oxidized nitrogen at the threi
ground stations based on a subset of al
photochemically active days. The per
centage of the total measured nitroger
contributed by each compound is showr
in parenthesis.
Particulate N03" exhibited a strong east
west gradient in the Los Angeles basin, it
contrast to S04=, which was relative!'
uniform. The average accountability o
total aerosol nitrogen as N03" and NH4"
ranged from 70-85% for the three grounc
stations. On the average, 47% of the N03~
90% of the S04=, and 100% of the NH4'
particles were < 2.0 /xm in size at thi
Upland site.
When both gas and aerosol species an
considered, the ratio of measured sulfu
compounds to nitrogen compounds h
quite close to the SO,/NOX emission inven
tory ratio. The data confirm the earlie
finding that most of the urban N03" i:
present in the gas phase. Table 2 show:
the fraction of urban N03" that exists ii
gaseous form for several cities.
Based on upwind tracer/NOx ratios, thi
calculated nitrogen mass balances for thi
Upland and Rubidoux sites show tha
^90% of the nitrogen is accounted for.
PAN + HN03
I/I
'o>
Los Angeles
Glendale ^ !<*
' Pasadena . $ / /O\
• fAzusa ^i ^g; San Bernardino
/T\ / • Upland •
j^Jj .W. Covina I
El Monte Pomong. i San_Bernardino
r- \Riversh
Q\afliverside
T
Torrance
Figure 1. Locations of three ground monitoring stations in the Los Angeles basin.
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Table 1. Average Daytime Distribution of Oxidized Nitrogen at Three Ground Stations*
Sites
Pollutant
Temple City
Upland
Rubdioux
NO
NO2
PAN
HONO2
N03
21 ppb (19%)
87 ppb (78%)
3 ppb (3%)
<6ppb(-)
0.8 ppb (1%)
5 ppb (10%)
33 ppb (66%)
1 1 ppb (22%)
<6ppb(-)
0.6 ppb (1%)
<5 ppb -
41 ppb (78%)
5 ppb (10%)
<6ppb(-)
6. 1 ppb (12%)
* Based on 11 photochemically active days.
Table 2. Fraction of Urban NO3~ in Gaseous Form
Site Location
Date
Gaseous N03'/Total /VO/
Ratio
St. Louis. Missouri
West Covina, California
Phoenix, Arizona
Temple City, California
Upland, California
Rubidoux, California
Beverly, Massachusetts
1973
1973
1977
1976
1976
1976
1978
0.95
0.98
0.50
0.75
0.96
0.45
>0.95
At both downwind sites (Upland and
Rubidoux), NOX conversion averaged 22%.
Using average reaction times for air masses
transported to these sites, a lower limit
transformation rate of 0.02-0.03 Ir1 is
calculated. On individual study days the
NOX removal rate reached 0.16 rr1, and
the rate of transformation to PAN ranged
from 0.01 to 0.08 hr1.
This publication is a brief summary of
the complete project report, which can be
purchased from the National Technical
Information Services.
Chester Spicer, Darrell Joseph, and Gerald Ward are with Battelle Columbus
Laboratories. Columbus, OH 43201.
W. A. Lonneman is the EPA Project Officer (see below).
The complete report, entitled "Studies of NO* Reactions and Oa Transport in
Southern California - Fall, 1976," (Order No. PB 83-200 360; Cost: $25.00,
subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA22161
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
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