United States
                   Environmental Protection
                   Agency
Atmospheric Sciences Research
Laboratory
Research Triangle Park NC 27711
                   Research and Development
 EPA/600/S3-85/029  June 1985
&EPA         Project Summary

                   Outdoor  Smog  Chamber
                   Experiments to Test
                   Photochemical  Models:
                   Phase  II

                   H. E. Jeffries, K. G. Sexton, R. M. Kamens, and M. S. Holleman
                     The smog chamber facility  of the
                   University of North Carolina at Chapel
                   Hill (UNC) 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
                   supporting 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, 128 dual-experiments
                   were performed using NO« and various
                   hydrocarbons  and hydrocarbon mix-
                   tures. The experiments performed dur-
                   ing this three-year project  have been
                   added to the existing UNC database for
                   model validation testing, bringing the
                   total  number of  dual-experiments to
                   346.
                     This report presents an organizational
                   scheme for these 346 experiments. Six
                   attributes of each experiment were used
                   for classification. These  are class of
                   experiment, experimental conditions,
                   quality, processing status, project that
                   produced the data, and membership in a
                   run series. Run series, a  collection of
                   experiments performed  in a certain
                   manner or addressing a particular ques-
                   tion,  formed  a major organizational
                   basis. Forty series were used, including
                   seven types of side-by-side series, four
                   types of chemical issues series, and five
types of characterization series. All dual
experiments, or runs, were classified
into one of the side-by-side series. Each
run could also appear in up to two addi-
tional series.
  The report also discusses three  ex-
amples of selecting runs to test mecha-
nisms. The examples are: runs to test an
explicit toluene chemistry mechanism;
runs to test mechanisms under dynamic
operating conditions; and runs to test
EKMA-type mechanisms for air quality
modeling. Recommendations for how
best to take advantage of the side-by-
side nature of the UNC runs in testing
mechanisms are given throughout the
discussion.
  This Project Summary was developed
by EPA's Atmospheric Sciences Re-
search  Laboratory, Research Triangle
Park, NC, to announce key findings of
the research project that is fully docu-
mented in a separate report of the same
title (see Project Report ordering infor-
mation at back).


Introduction
  Photochemical kinetics reaction mod-
els  are central components in EPA's
method for computing  control require-
ments for organic emissions needed to
meet the National Air Quality Standard
for ozone. State and local control officials
are expected to use these models to esti-
mate control requirements. However, dif-
ferent kinetic models  apply different
methods, often resulting in different des-
criptions of the same situation.  Smog

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cha mber data must be used to test photo-
chemical mechanisms to determine the
adequacy of the chemical representation.
Presently,  mechanism  testing has not
used a large enough range of test data
encompassing the range of conditions
likely to occur in an urban control situa-
tion. This is because, in part, an organized
database containing the range of condi-
tions needed was not  available before
now.
  This report uses a hierarchy of chemi-
cal species, based on  the number of
hydrocarbon and oxides of nitrogen
(HC/NOx) systems in which the species
occur, to determine  the type of smog
chamber experiments needed for ideal
mechanism validation. This species hier-
archy included a hierarchy of operating
conditions.  These four sets of conditions,
which include large dilution and continu-
ous injection, are ordered to proceed from
the standard smog chamber type experi-
ment to conditions  that simulate  the
urban environment. All experiments took
place under natural sunlight and ambient
temperature. An  example of this hier-
archy of experimental conditions is shown
in Figure 1,  in which a similar photochem-
ical system  was performed under four dif-
ferent physical conditions. Two of these
experiments also show the unique side-
to-side nature of the UNC chambers.
  Three  other projects using the UNC
Outdoor Smog Chamber have contributed
data for model testing. The types of data
provided by these projects are described'
briefly in this report, and the project iden-
tifications are used in the classification
scheme.

Purpose
  The purpose of this research  project
was to: (1) measure react ant and product
concentrations as functions of time in
selected  photochemical  smog systems;
(2) process these data into a form readily
distributable to model  developers and
testers; and (3) provide auxiliary informa-
tion needed to create mathematical model
descriptions of  the systems. The 128
dual-experiments,  when added  to  the
other experiments in the database,  en-
compass a  range of complexity from
single HC species in totally static situa-
tions to  complex urban mixtures  in fully
dynamic conditions. As a whole, the data
set is well suited to develop and test
models  of  chemical transformations in
polluted atmospheres.

Organizing Principles
  The 346 runs were classified by "keys"
to allow easy  selection. Six kinds of
 attributes were used to organize the runs
 in the data set. The C/ass of a run was
 either a characterization run that ad-
 dressed unique aspects of  the  UNC
 chamber or organic/NOx runs  to test
 mechanism  design. Further,  either  of
 these types could be one-day or multi-day
 runs. Experimental  Conditions were
 based on four major types of run condi-
 tions. These conditions were: dilution
, (large or normal),,injection (initial or con-
 tinuousK and type of HC system used, i.e.,
 single HC  species or  mixture, and, if a
 mixture, whether  the  composition was
 constant or varying over time. Initial Con-
 ditions included the exact NOX and HC
 concentrations that occurred on  both
 sides, as well as the identity of the HC for
 up to three HC species. For runs that had
 more than three  species,  HC mixture
 names were used. The Quality of a run
 was rated on a scale of 0 to 9. The major
 determining factors for quality were the
 weather conditions and the number and
 performance of the  analytical  instru-
 ments. The Processing Status of a run
 indicated the availability of validated data
 on tape or in other forms such as plots. All
 runs  were  included in the database, but
 not all  have yet been completely pro-
 cessed to the final validated form. The
 Project Name identified the runs by the
 project that produced the experiment.


 Data Set
   The report describes  how  the  runs
 were distributed across the organization
 keys  set forth. The majority of the experi-
 ments were one  day, normal dilution,
 initial injection runs performed between
 June and October. The experiments were
 summarized by HC type. All the species
 and named mixtures used are listed. The
 grading  of experiments  is  explained:
 important  factors are sunlight, initial
 conditions, analytical support, chamber
 conditions, and need/usefulness.  Most
 runs  were graded at 7 or 8.
   All experiments in the data base are
 listed two  ways: sorted by series and by
 species. The seven types of series lists
 are characterization, matched conditions,
 relative reactivity between sides, carbon
 substitution, carbon addition, delta con-
 centration of HC or NOx, and static-to-
 dynamic transition experiments. The five
 species  lists are: formaldehyde, acetal-
 dehyde, ethylene, propylene (other than
 matched propylene) and toluene. These
 lists include all experiments in which the
 species  appeared, alone or in mixtures,
 on either  side of the chamber. Within
 each series and species list, the runs are
grouped by HC type beginning with the
simplest type that appears in the series
Within the HC type, the runs are in chro-
nological order. Guidance for the useful-
ness of a specific run for the purpose ol
model  testing is also given in terms ol
general ranking categories.

Selecting Runs and Obtaining
Data
  Using three examples,  the report illus-
trates  how experiments from the UNC
Smog Chamber Database might be se-
lected to test  mechanisms. General rec-
ommendations and assumptions are de-
fined to guide modelers in general selec-
tion. The  examples discussed involved
the testing of  an explicit toluene reaction
mechanism, a mechanism under dynamic
conditions, and an EKMA-type  mecha-
nism for urban conditions.
  The data set described in this report is
neither complete nor static. New projects
are adding to this data set, and the exist-
ing runs are under constant review and
analysis.  The possibility for,  and the
means of, future revisions are explained.
  This  data  set has been supplied  to
modelers for analysis under EPA Contract
Nos. 68-02-3738 and 68-02-4104. The
purpose of this report is to describe the
data set and to provide guidance so others
in the  scientific community can use  it.
Fully processed runs and the experimen-
tal conditions database are available on
an ANSI formatted magnetic tape. Copies
of the tape and other supporting informa-
tion are available through the authors.

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                    8     10    12    14     16    18
                            Hours, EOT
                                                                      10    12   14     16    18
                                                                        Hours, EOT
Figure  1.
Outdoor smog chamber runs as examples of hierarchial experimental conditions.  The NOi concentration was <=*0.25 ppm, HC
concentration =2.6 ppmC of propylene/n-butane/toluene mixture. Large dilution means that 20% of initial mass is left after 10 hours
of dilution fequivalent to mixing height rise from 250 m to 1250 m).
  H. E, Jeffries. K. G. Sexton. R. M. Kamens. and M. S. Holleman are with the
    University of North Carolina. Chapel Hill. NC 27514.
  Marcia C. Dodge is the EPA Project Officer (see below).
  The complete report,  entitled "Outdoor Smog Chamber Experiments to Test
    Photochemical Models: Phase II," (Order No. PB 85-191 542/A S; Cost: $ 19.00,
    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:
          Atmospheric Sciences Research Laboratory
          U.S. Environmental Protection Agency
          Research Triangle Park, NC 27711
                                   •t, U.S. GOVERNMENT PRINTING OFFICE: 1985-559-016/27079

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