v>EPA
United States
Environmental Protection
Agency
Environmental Sciences Research x
Laboratory '/
Research Triangle Park NC 27711
Research and Development
EPA-600/S3-82-016a June 1982
Project Summary
Outdoor Smog Chamber
Experiments to Test
Photochemical Models
H. E. Jeffries, R. M. Kamens, K. G. Sexton, and A. A. Gerhardt
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The smog chamber facility of the
University of North Carolina (Chapel
Hill) was used in a study to provide
experimental data for developing and
testing kinetic mechanisms of photo-
chemical smog formation. The smog
chamber, located outdoors in rural
North Carolina, is an A-frame structure
covered with Teflon film. Because the
chamber is partitioned into two sec-
tions, each with a volume of 156 m3,
two experiments can be conducted
simultaneously. The dual chamber is
operated under natural conditions of
solar radiation, temperature, and rela-
tive humidity. In this study, 115 dual
all-day experiments were conducted
using NOX and various organic spe-
''/?,, cies. The organic compounds investi-
^> gated included various paraffins,
olefins, aromatics, and oxygenates,
both singly and in mixtures of two or
more components-.
This report describes the data col-
lected over a three-year period of the
study. The experimental procedures
and analytical methods used in this
study and the limitations and uncer-
tainties of the data are discussed. Guid-
ance for modeling of the data is also
given, including a detailed discussion
of how to estimate photolytic rate
constants from the available ultravi-
olet and total solar radiation data and
how to treat such chamber artifacts as
dilution, wall sources and losses of
pollutants, and reactivity of the back-
ground air.
This Project Summary was devel-
oped by EPA's Environmental Scien-
ces Research Laboratory. Research
Triangle Park. NC. to announce key
findings of the research project that
is fully documented in a separate re-
port of the same title (see Project Re-
port ordering information at back).
Introduction
A long-term goal of EPA's research
program is to develop urban and
regional air quality simulation models
(AQSMs) for planning accurate and
scientifically-defensible control strat-
egy. Because the pollutants with the
greatest health effects are secondary
pollutants, formed by chemical reac-
tions occurring in the atmosphere, an
understanding of the chemistry that pro-
duces these pollutants is critical to the
development of AQSMs. In recent years
significant effort has been made to
explain the chemical transformations
that occur in photochemical smog sys-
tems and to develop chemical kinetic
mechanisms that can be used in the
AQSMs to explain the formation of
ozone and other secondary pollutants.
Despite the progress that has been
made towards an understanding of the
chemical processes that lead to the for-
mation of photochemical smog, there is
still a need for a comprehensive and
well-characterized data base to serve as
a benchmark from which kinetic models
may be experimentally tested. The pur-
pose of this study was to acquire such a
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data base. Because the ultimate goal of
this research is to produce kinetic mod-
els that can simulate the processes
occurring in the polluted environment,
it was important to acquire the data
under conditions that were as closely
representative as possible of actual
atmospheric conditions. For this reason,
the dual outdoor smog chamber facility
of the University of North Carolina,
which is operated using actual sunlight,
temperature, and water vapor condi-
tions, was selected for this study. The
study was performed by the University
of North Carolina (Chapel Hill) under
Cooperative Agreement No. 805843.
Procedure
The experiments were conducted in
an outdoor A-frame smog chamber
covered with Teflon (registered trade-
mark). A Teflon panel divided the
chamber into two sections, each with a
volume of 156 cm3. The chamber was
purged overnight with the relatively
clean air that prevails at the site in rural
North Carolina. Shortly before sunrise,
the chamber doors were sealed and the
reactants of interest were slug-injected
into the chamber. The usual procedure
was to inject the same concentration of
NOX into both sides of the chamber and
then vary the concentration or identity
of the hydrocarbon in the two sides of
the chamber. The chemical constituents
and physical parameters were moni-
tored from the time the reactants were
injected until about 6:00 p.m. EOT. A
computer-based data-acquisition and
control system was used to acquire, pro-
cess, and record data from the chamber
instrument system. Instruments were
used to measure NO, NO2, 03, PAN,
HNO3, alkyl nitrates, HOOH, CO, indi-
vidual hydrocarbons, aliphatic and aro-
matic aldehydes and other oxygenates,
such as phenol, acetone, and methyle-
thylketone. Standard meteorological
instruments were used to measure
solar radiation, ultraviolet radiation,
temperature, and dew point.
The experiments took place between
May 1977 and August 1980. Of the 115
dual runs conducted in this study, 98
were performed during the June-
through-October smog season and 17
were conducted during the winter and
spring period from November through
May. The reactivities of 18 individual
organic compounds and 14 mixtures of
two or more organic species were inves-
tigated. The organic compounds and the
mixtures included in this study are
shown in Table 1.
Table 1. Organic Components Used in the Outdoor Smog Chamber Experiments.
Single Components Mixtures
Formaldehyde
Acetaldehyde
Biacetyl
Methyl glyoxal
Benzaldehyde
Methylethylketone
Acetone
Ethylene
Propylene
Butane
Pentane
2,3-Dimethylpentane
Octane
Toluene
o-Xylene
Isoprene
Alpha-Pinene
Butyl nitrate
Formaldehyde/MEK
Formaldehyde/A cetone
Formaldehyde/Benzaldehyde
Ethylene/Formaldehyde
Ethylene/A cetaldehyde
Ethylene/ Trichloroethylene
Ethylene/Trans-2-butene
Prop ylene/Formaldeh yde
Propylene/Acetaldehyde
Prop ylene/B utane
Propylene/ Toluene
Toluene/Benzaldehyde
A Ipha -Pinene/'Isoprene
Urban Mix
Results
The data collected in this study are
available in several forms. Included in
the project report are hourly data list-
ings and plots of concentration as a
function of time for 10 experiments that
a re representative of the entire data set.
In general, these runs have reasonably
complete product information, were
conducted under favorable sunlight
conditions, and offer the modeler a wide
range of initial conditions. Also con-
tained in the report are a collection of
plots illustrating interesting features of
the data set. Included in the report are
illustrations of the following:
(1) Selected n-butane, n-pentane, n-
octane and 2, 3-dimethylbutane
runs and the carbon-containing
products identified in these experi-
ments.
(2) Selected aromatic runs, including
toluene/NOx runs, in which the
intent of the experiments was to
determine the relative yields of
benzaldehyde and cresol and to
identify ring-cleavage products
such as methyl glyoxal.
(3) Experiments demonstrating the
effect of adding formaldehyde or
acetaldehyde to the propylene/NO*
system.
(4) Experiments to assess the effect of
relative humidity on the propylene/
NOX system. In these experiments
the air on one side of the chamber
was dried by passing it through
refrigeration cooling coils and the
other side of the chamber was left
undried.
In addition to the data for selected
runs that are included in the text of the
project report, the data are also avail-
able as: (1) a computer-readable mag-
netic tape containing all data for all 115
dual experiments and (2) a set of micro-
fiche of listings and plots of the entire
data base. Both the computer magnetic
tape and the microfiche are available
through the National Technical In-
formation Service, Springfield, VA, as is
the project report (see the ordering in-
formation at back).
In addition to a detailed discussion on
how to access and use the data, the
report also contains a complete descrip-
tion of the chamber facility, the pro-
cedures and analytical methods used in
the study, and the uncertainties and
limitations of the data base. Guidance
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for modeling of the data is also given
including detailed discussions of how to
treat light intensity data, rates of loss of
Os and NOX to the chamber walls, walls
as a source of free radicals, chamber
dilution, temperature and water vapor
data, and reactivity of the background
air.
Conclusions
Smog chamber data collected in this
study were supplied to two model
development groups for analysis under
EPA Contract Nos. 68-02-3281 and 68-
02-3479. The analysis of these data by
the two modeling groups resulted in
the development of improved kinetic
models of photochemical smog for-
mation. The purpose of the project
report is to make the experimental data
available to the scientific community at
large to enable other researchers and
modelers to further the development of
chemical transformation models.
H. E. Jeffries, R. M. Kamens, K. G. Sexton, and A. A. Gerhardt are with the
University of North Carolina. School of Public Health, Chapel Hill. NC27514;
Marc/a C. Dodge (also the EPA Project Officer, see below) is with the Environ-
mental Sciences Research Laboratory. Research Triangle Park, NC 27711.
The complete report, entitled "Outdoor Smog Chamber Experiments to Test
Photochemical Models," (Order No. PB 82-198 508; Cost: $22.50, 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
„ US GOVERNMENT PRINTING OFFICE. 1W2-559-017/0740
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