EPA-R4-73-010
January 1973 Environmental Monitoring
Workshop
on Mathematical Modeling
of Photochemical Smog:
Summary of the Proceedings
Office of Research and Monitoring
National Environmental Research Center
U.S. Environmental Protection Agency
Research Triangle Park, N.C. 27711
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EPA-R4-73-010
Workshop
on Mathematical Modeling
of Photochemical Smog :
Summary of the Proceedings
October 30-31, 1972
by
Marcia C. Dodge
Chemistry and Physics Laboratory
National Environmental Research Center
Research Triangle Park, North Carolina 27711
National Environmental Research Center
OFFICE OF RESEARCH AND MONITORING
U.S. ENVIRONMENTAL PROTECTION AGENCY
RESEARCH TRIANGLE PARK, NORTH CAROLINA 27711
January 1973
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TABLE OF CONTENTS
Page
I. STATE OF THE ART
A. Introduction
B. State of the Art of Photochemical Modeling
Philip M. Roth
C. State of the Art of Atmospheric Chemistry
Thomas A. Hecht 10
II. THE ROLE OF KINETIC STUDIES IN MODELING
A. Photolysis of N02 12
B. Reaction of 03 and N02 12
C. Reaction of N205 and H20 13
D. Reaction of OH and CO 14
E. Reaction of H02 and NO 15
F. Reaction of Olefins and 0 Atoms 15
G. Reaction of Olefins and 0^ 16
H. Reaction of Olefins and OH 17
I. Reaction of Olefins and H02, RO, and R02 17
J. Reactions of Alkoxy Radicals 17
K. Photolysis of Aldehydes 18
III. THE ROLE OF SMOG CHAMBER EXPERIMENTS IN MODELING
A. The Modeling of Smog Chamber Data
1. Alan Eschenroeder 19
2. Thomas A. Hecht 21
3. Lowell G. Wayne 23
Discussion 25
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B. Proposed Smog Chamber Study to Aid in the Modeling
Effort - Harvey Jeffries 26
C. The Role of Aerosols in Photochemical Smog
Arthur Levy 28
IV. THE ROLE OF ATMOSPHERIC MEASUREMENTS IN MODELING
A. Recommendations for Future Field Studies
Alan Eschenroeder 30
Discussion 32
B. Los Angeles Reactive Pollutant Study
William A. Perkins. 34
C. Coupling of the Photochemistry to an Airshed Model
Ralph C. Sklarew 35
Discussion 37
D. Summary 39
APPENDIX A.
The Chemistry of Photochemical Smog Formation A-l
APPENDIX B.
Workshop Participants B-l
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I. STATE OF THE ART
A. Introduction
This workshop on the modeling of photochemical smog formation
was held for two principle reasons. One purpose was to establish
lines of communication between the experimentalist and the modeler....
between the person gathering the data and the person who is using
i
the data to formulate a photochemical model. In the past there had
been too little interaction between the groups. It was important
to define the problems facing both the experimentalist and the
modeler, to recognize the limitations of each endeavor and to
determine what could and what could not be accomplished.
Realizing that more research must be undertaken before the
full potential of modeling can be realized, the second purpose of
this meeting was to determine those key areas where further research
is needed.... to determine how best to attack the problem of providing
the necessary data to enable development of a model capable of pre-
dicting air quality.
The Chemistry and Physics Laboratory has an extensive
program underway to elucidate the chemistry of photochemical smog
formation. The Laboratory carries out research in two principle
areas; it develops information on the chemical and physical trans-
formations that pollutants undergo in the atmosphere and it develops
techniques and instruments for the measurement of these pollutants.
Some of the activities that the Laboratory is engaged in to furnish
information on atmospheric chemistry are the following:
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1. Smog chamber studies to....
(a) Investigate the relationship between hydrocarbons
and the rate of conversion of NO to N02-
(b) Determine the role of aerosols.
(c) Identify SOo removal and oxidation processes.
2. Field studies to determine....
(a) Background levels of hydrocarbons.
(b) Transport of 63 beyond an urban area.
(c) Fate of reactive pollutants.
3. A 5-year Regional Air Pollution Study of St. Louis
during which the Chemistry and Physics Laboratory will be per-
forming such tasks as....
(a) Field testing new analytical instruments.
(b) Measuring trace gases, such as acetylene and
CO, to determine the contribution of auto exhaust to urban pollution.
(c) Performing detailed compositional analyses of
hydrocarbons.
(d) Determining the mass and size distribution,
concentration and chemical composition of aerosols.
4. The development of new instrumentation to aid in the
detection of atmospheric pollutants. Some of the instruments
under development are....
(a) Fourier Transform Infrared Spectrometer coupled
to a long path cell for the analysis of trace constituents at the
ppb level.
(.b) High energy light sources such as tunable diode
lasers for in situ measurements of gaseous pollutants.
(c) New optical techniques such as remote lidar
systems for measuring stack effluents and particulates.
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(d) New instruments to aid in the characterization
of aerosols.
In addition to the above areas of research, the Chemistry and
Physics Laboratory has recently initiated a program to develop the
optimum photochemical mechanism that can be satisfactorily coupled
with emission and meteorological models to assess air quality. In
addition to plans currently underway to carry out new smog chamber
studies and to measure rates of reaction, a contract has been
awarded to develop such a photochemical mechanism and to test this
mechanism against chamber data. Because of this commitment to
modeling and a desire to concentrate efforts in a manner that will
yield the most critically needed information, this workshop was
organized with the hope that the resulting discussions would aid
in developing future directions for the modeling effort.
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B. State of the Art of Photochemical Modeling - Philip M. Roth
Systems Applications, Inc., with P. Roth
as project officer, is currently under
contract to the Chemistry and Physics
Laboratory to develop a photochemical
mechanism and to test this mechanism
using smog chamber data.
P. Roth began his presentation on the state of the art of
photochemical modeling with a description of the use of models as
predictive tools. One use of models is to simulate the effects of
alternative air pollution control strategies on pollutant concen-
trations. Another use of models is for land use planning so that
projected freeways and power plants may be located where their
air pollution potential is minimized. Models can be used for
planning long-term control strategy to accomplish air quality
objectives at least cost. Another use of models is to enable real-
time prediction in an alert warning system to anticipate impending
air quality episodes. ;
Several types of models have been formulated in an effort
to meet these modeling needs. The simplest of these is the box
model, where pollutant concentrations are assumed to be homogeneous
throughout the entire airshed. A second type of model, developed
to describe the concentration of inert species downwind of a point
source, is the gaussian plume model. Both of these models are
too simple to meet the requirements of modeling. A more complex
approach is one based on the solution of the equations of continuity.
This approach provides the means for including chemical reactions,
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time-varying meteorological conditions, and complex source emission
patterns. Finally, the most complex model proposed involves the
solution of the full boundary layer equations for the conserva-
tion of mass, momentum and energy. Since the solution of these
equations exceeds the capabilities of present generation computers,
the thrust of the current program is on developing models based
on the solution of the continuity equations.
Two main types of airshed models, based on the solution of
these continuity equations, are currently under development.
One is the trajectory or moving coordinate approach where a
hypothetical column of air is followed through the airshed as it
is advected by the wind. This model is useful for describing the
concentration of species downwind of a point source, line source
or area source. The other is the grid or fixed coordinate approach
where the airshed is divided into three-dimensional cells, each
cell perhaps one or two miles on a side and about 100 feet high.
This model is useful for describing pollutant concentrations
throughout the airshed. These two approaches are based on the
finite difference solution of the equations of conservation of mass.
These equations are composed of....
1. terms to describe how pollutants are transported by
winds and dispersed by turbulent air motions
2. source terms to describe the influx of new pollutants
3. sink terms to account for the removal of materials
...and 4. chemical reaction terms.
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For every chemical species in the mechanism, a differential
equation must be written. Since these equations are coupled
through the reaction rate terms, they must be solved simultaneously.
Therefore, the time for solution increases with each new species
added to the mechanism. For this reason, it is crucial to use
as few species as possible in formulating a mechanism. At the
same time, however, a sufficient number must be included in order
to maintain some semblance of reality. In essence, it is necessary
to achieve a proper balance between chemical accuracy in prediction
and computational simplicity, remembering that the kinetic model
is only one part of the overall airshed model.
There are many uncertainties associated with the various
input variables to this conservation of mass equations. Emission
strengths are imprecisely known. For example, auto emissions
are estimated from a laboratory driving cycle which may or may not be
representative of actual driving patterns. Meteorological con-
siderations introduce a large uncertainty. Information on such
variables as inversion heights, boundary conditions and wind speeds
aloft is scanty. There is considerable uncertainty in the air
quality data. The accuracy of the data, the frequency of the
measurements, and the number and distribution of the sampling sta-
tions in general is inadequate.
Another area of uncertainty and the area this workshop
addressed itself to is the chemistry of atmospheric transformation
processes. A number of unresolved problems are associated with
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this complex subject. The role of aerosols in smog formation has
not been elucidated satisfactorily. The effects of the size, mass,
and chemical composition of aerosols on atmospheric processes are
not well defined. Likewise, the role of SC>2 in photochemical smog
formation is not well characterized. For these reasons, neither
S02 nor aerosol chemistry has as yet been modeled. Little is known
about sinks for pollutants. The importance of soil as a sink for
CO and of vegetation as a sink for SC>2 and N0Ł has not been deter-
mined. The rates of a number of chemical reactions and the
elementary steps and reaction products of certain other reactions
are unknown. Some species suspected of playing a role in smog
formation, such as HN03, have not been detected in the atmosphere.
The effects of temperature, especially on the heterogeneous reactions,
have not been determined. Plume chemistry is little understood.
The effect of high temperature and high concentrations on the
chemistry of stack effluents is not well defined. These problems
demonstrate how difficult it is in some cases to relate the chemistry
occurring in smog chambers to that which is occurring in the
atmosphere.
The successful development of a comprehensive airshed model
depends heavily on the accurate description of reaction rate
processes. Only in the last several years have investigators
postulated general kinetic mechanisms to describe the rates of
chemical reactions in the atmosphere. Three classes of mechanisms
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have been postulated to explain atmospheric chemistry. There were
the early mechanisms of Friedlander and Seinfeld, Eschenroeder,
and Behar that were highly simplified, consisting of fewer than
ten reactions. Later in the development came less simplified
mechanisms consisting of 10-25 steps. The Hecht and Seinfeld
and the Eschenroeder and Martinez mechanisms fall in this category.
Also developed at this time were the highly complex mechanisms such
as Wayne's 33 step mechanism, Niki's 60 step propylene mechanism,
Calvert's multistep mechanisms, Levy's tropospheric model and
Johnston's stratospheric model. Only the mechanisms of Hecht and
Seinfeld, Eschenroeder and Martinez, and Wayne have been incorporated
into urban airshed models.
Since for each species added to the mechanisms, a new
equation must be written and solved simultaneously with the other
equations, lumping is desirable. There are various ways to lump.
Fast and slow reactions can be combined, thus eliminating the fast
reacting intermediates. Hydrocarbons may be lumped, either as
a single "species" or perhaps one "species" for olefins, one for
aromatics, and one for paraffins. Radicals may be lumped into
general classes such as alkyl, alkoxy and peroxy. Steady-state
assumptions can be made to eliminate differential equations for
transient species such as 0 atoms and OH radicals. One of the
more difficult problems facing the modeler is determining just
what lumps should be used. It is a formidable task both to select
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the groupings and to decide what parameters for these groupings
should be employed in the rate expressions.
Once a mechanism has been formulated, it is necessary to
test this mechanism against laboratory data. The determination
of just what experimental programs should be undertaken to
facilitate the validation of these photochemical models was a
prime objective of this workshop.
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C. State of the Art of Atmospheric Chemistry - Thomas A. Hecht
T. Hecht is a graduate student at the
California Institute of Technology
who, in conjunction with Professor
John Seinfeld, has developed a
generalized mechanism for photochemical
smog formation. He is currently a
consultant to Systems Applications, Inc.,
assisting P. Roth in carrying out
further refinements of the chemical model.
T. Hecht distributed a list of some 40 reactions that
are either known or suspected to be of importance in explaining
the chemical processes occurring in polluted atmospheres [see
Appendix A]. He discussed these reactions, emphasizing the
uncertainties that are associated with each. He pointed out
those reactions for which the rate constants are either unknown
or the rate constants are imprecisely determined, and therefore
highly suspect. Those reactions for which the intermediates and
products of reaction are unknown were also discussed and possible
mechanisms for each were offered.
In addition to discussing each reaction in detail, Hecht
raised several questions on the possible effect of particulate
matter and surface area atmospheric reactions. Do particles
accelerate the oxidation of NO? Do they terminate radical chains?
How does the water content of particles and size, number and
chemical composition of aerosols influence atmospheric reaction?
The problems of relating smog chamber chemistry to
atmospheric processes were mentioned. The possible effects of
surface-to-volume ratio, stirring of the chamber, nature of the
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walls, and the relationship between the chamber hydrocarbon
compositions and their concentrations to those of the atmosphere
were discussed. Questions were raised on the possible effect
of H20, temperature and light intensity on the rates of reaction.
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II. THE ROLE OF KINETIC STUDIES IN MODELING
An open discussion was held of each of
the reactions listed in T. Hecht's
handout [see Appendix A]. The following
is a brief description of some of the
more important reactions considered and
the comments that were raised.
A. Photolysis of N02
The point was raised that the results of validation
studies indicate that k&0 for the reaction N02 + hv * NO + 0 is
one of the most important parameters in a smog chamber experiment
Small changes in ka0 in the simulations produce large changes
in the time to the N0Ł maximum and the amount of Oj formation.
The rate of photolysis in both smog chamber experiments and in
the atmosphere is uncertain by about 20%. W. Perkins discussed
his plans for developing a new actinometer for use in the field
that will measure the rate of dissociation of N0Ł in an atmosphere
of nitrogen. T. Hecht mentioned the difficulty of relating k
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of the reaction 0-j + NC^ + N03 + GŁ have been made. Johnston and
Yost obtained k = 0.11 ppm"1 rain"1 and Ford et_ al_ measured
k = 0.048 ppm min~ . The point was raised that some modelers
are finding that the build-up of 0-j is underestimated when even
the smaller of these measured values is used in their simulations,
H. Johnston pointed out that he is re-investigating this reaction
and that preliminary results indicate that his earlier value
may be too high. However, H. Niki who also is re-investigating
this reaction indicated that his results support Johnston's
earlier value. Johnston suggested that perhaps the photolysis
of NOo should be taken into account to reduce the NO^ levels in
the simulations and thereby increase the predicted levels of
ozone to bring them more in line with the experimental results.
C. Reaction of ^05 and
The only measured value of the reaction ^05 + HnO ->
2HN03 is Jaffe and Ford's value of 2.5 x 10~3 ppm'1 min"1.
H. Johnston pointed out that this reaction does not take place in
the gas phase but occurs only on surfaces. It is agreed that this
reaction does take place in both the atmosphere and in the smog
chamber. The difficulty comes in trying to asses the relative
importance of this reaction in the two environments. H. Niki
felt that heterogeneous reactions occur to a greater extent in
the smog chamber than in the atmosphere. The surface-to-volume
ratio in a smog chamber is greater than in the atmosphere even
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though the atmospheric particulate loading is high. A. Eschenroeder
supported this view. A.P. Altshuller raised the issue that it is
not only the particulate matter in the atmosphere that must be
considered, but also, one must take into account the many rough
surfaces at ground level which offer ready sites for heterogeneous
reactions.
H. Levy pointed out that, on the basis of some calculations
he has made, he estimates the atmospheric concentration of HNO^
to be 50 ppb. P. Hanst spoke of the Laboratory's long path infrared
system and the attempt to see HNO^ in the gas phase. Largely
because of instrumental problems, this endeavor has been unsuc-
cessful to date. It was agreed by most in attendance that every
effort to measure HNOj in the atmosphere and every means to deter-
mine the effect of various surfaces on the rate of this reaction
should be made.
D. Reaction of OH and CO
The rate constant for the reaction OH + CO -ť- C02 + H is
fairly well established to be 240 ą 30 ppm'* min . The point in
some dispute is whether or not this reaction is of any importance
in the atmosphere. Several investigators have found that this
reaction does not compete with the much faster olefins and OH
reactions. J. Bufalini pointed out that experiments conducted in
the large irradiation chamber at realistic concentrations showed
that, even when only paraffins were present, 20 ppm CO had to be
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added to the system before an effect could be observed. W. Wilson
pointed out that, while this reaction is probably unimportant in
urban areas, it could play a late-time role in rural areas where
the reactive pollutants have been depleted and CO could compete with
the slower reacting hydrocarbons for OH radicals. It was pointed
out that since the concentration of CO can be lumped into the rate
constant, this reaction adds no new species to a generalized smog
mechanism and its inclusion in the reaction scheme will not
significantly increase computational time. Therefore, this
reaction probably should be left in the mechanisms.
E. Reaction of H02 and NO
The rate of the reaction H02 + NO > OH + NO-, is largely
unknown. There are several estimates of this rate constant in
the range of about 500 ppm~l min . If this reaction is the only
one of any importance in the atmosphere for the removal of H02,
then it is not necessary to know precisel) the rate of this reaction
The only other suggested removal path for W^ is the reaction of
H02 with olefins. D. Hendry mentioned that he is currently looking
into the rates of H02 and olefin reactions in the liquid phase and
his preliminary results indicate that these reactions are extremely
slow, of the order of only 10"^* ppm"* min'l.
F. Reaction of Olefins and 0 Atoms
Rate constants have been measured for most hydrocarbon - 0
atom reactions of atmospheric interest. The uncertainties lie,
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not with the rate constants, but rather with the products of the
reaction of olefins with 0 atoms in the presence of 0ť. Modelers
are presently limited by a lack of information on the free radical
intermediates of olefin - 0 atom reactions. The results of the
simulations are quite dependent on the chain lengths of free
radicals that are assumed in the model. It was brought up that
chain initiation by olefin - 0 atom reactions may be more important
in smog chambers than in the atmosphere. H. Johnston pointed out
that in the atmosphere there is a ready source of OH radicals from
the photolysis of MONO which can initiate smog formation. Since
reactions of OH radicals with hydrocarbons are several orders of
magnitude faster than reactions with 0 atoms, initiation by 0 atoms
in the atmosphere may be of minor importance. However, it was
agreed that, if possible, the mechanism of olefin and 0 atom
reactions in the presence of 02 should be investigated. As
D. Hendry pointed out, this is no easy task since, as soon as 02
is introduced, Oj is formed and one is faced with the task of
sorting out the olefin - Oj reactions.
G. Reaction of Olefins and 03
It is known that Oj adds to olefins to form a zwitterion
or a biradical type intermediate, but the subsequent reactions of
this intermediate are unknown. Most in attendance felt that
olefin - Oj reactions are probably of less importance in the
atmosphere than in the smog chamber. However, it would help model
development to elucidate the mechanism and the products of reaction
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H. Reaction of Olefins and OH
All participants agreed that the most important free
radical responsible for hydrocarbon consumption is the hydroxyl
radical. While a number of rate constants for olefins - OH
reactions have been measured, the mechanism and the products of
these reactions under atmospheric conditions are unknown. Due to
the extreme importance of these reactions in smog formation,
major emphasis should be placed on elucidating the mechanisms
of these reactions.
I. Reaction of Olefins and H02, RO and R02
Of those in attendance, no one felt that the reactions of
hydrocarbons with species other than 0, 03 and OH are of significant
importance in explaining smog formation.
J. Reactions of Alkoxy Radicals
Three major reactions are postulated to account for the
disappearance of RO reactions:
RO + 02 -> H02 * aldehyde
RO + NO ^ RONO
RO + N02 -ť RON02
The rate constants for these reactions are unknown. It was agreed
that it is important to determine the relative ratio of these
reactions since the reaction of RO with 02 is chain propogating
whereas reactions with NO and N02 are chain terminating.
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K. Photolysis of Aldehydes
Of those in attendance, most felt that aldehydes play an
important role in smog formation. K. Demerjian commented that
a major part of the initial push to oxidize NO and olefins in the
atmosphere could come from the photolysis of aldehydes since one
of-the primary processes yields HCO radicals which in turn are
oxidized to HO?. J. Bufalini commented that studies carried out
in his laboratories showed that the presence of aldehydes had a
pronounced effect on the rate of reaction. He stated that when
acetaldehyde was added to a mixed hydrocarbon - NO system a
A.
rapid acceleration in the rate of oxidation of NO to N02 occurred.
However, when benzaldehyde was added to this system, a marked
decrease in the rate of oxidation of NO was observed and a significant
decrease in 03 formation occurred. It was agreed that the role
of aldehydes in smog formation deserves careful attention.
K. Demerjian and J. Pitts stated that the quantum yields of the
primary photolysis of aldehydes as a function of wavelength are
not well determined and should be further studied.
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III. THE ROLE OF SMOG CHAMBER EXPERIMENTS IN MODELING
A. The Modeling of Smog Chamber Data
For the past several years three groups
have been under contract with EPA to
develop photochemical models. As part
of this effort these concerns have been
testing their mechanisms with smog
chamber data furnished to them by
the Chemistry and Physics Laboratory.
The following reports are recommendations
that three of the individuals involved
in this modeling effort had to offer
regarding the type of smog chamber data
they feel is needed to aid in the
modeling effort.
1. Alan Eschenroeder - General Research Corporation
A. Eschenroeder had several suggestions on the type
of smog chamber data he feels would help in the validation of
models. Some of the suggestions he offered were:
(a) Analysis of reactants and products should be
made in situ if possible in order to yield real-time concentrations.
(b) In addition to gas-phase smog chamber experi-
ments, controlled investigations of the effects of aerosol should
be carried out. Aerosols should be introduced in a controlled
fashion into the chamber to determine the magnitude of heterogeneous
reactions.
(c) If possible, nitrogen balances should be
achieved in the chamber experiments in order that the wall effects
may be ascertained. At the moment, considerable difficulty is
being encountered by some of the modelers in attempting to sort
out the role of aerosol and wall reactions from gas phase reactions.
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(d) If possible, it would be of benefit to the
modeler in determining how valid his mechanism is to measure the
concentrations of the free radicals, especially hydroxyl and
alkyperoxyl radicals, to within an order of magnitude.
(e) It would be desirable to carry out smog
chamber experiments under conditions that would result in ozone
levels of the concentrations set in the air quality criteria
documents. The modelers are currently analyzing atmospheric data
that has Oj levels of 30 pphm. Their results cannot be extrapo-
lated down to the air quality levels of 8 pphm with any confidence
For small increments of control it is believed that the model can
be applied with confidence. However, for drastic changes in
pollutant levels, the uncertainty of the predictions is high.
(f) More information to aid in model development can
be gained through the study of the simpler systems, such as binary
hydrocarbon - NOX systems, than by attempting to fit the complex
systems such as smog chamber studies of dilute auto exhaust.
(g) Measurements of all major reactants and products
need not be measured to greater than 20% accuracy. It is important
that smog chamber experiments be designed that will afford this
accuracy of measurement.
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2. Thomas A. Hecht - Systems Applications, Inc.
The following are suggestions put forth by T. Hecht
as to the type of chamber data he feels is necessary to aid in
model validation.
(a) The relative humidity of the smog chamber
runs should be controlled and carefully measured.
(b) Temperature rise in the smog chamber should
be kept to a minimum. In order that the effect of increasing
temperature can be taken into account, the temperature should be
measured throughout the run.
(c) The light intensity of the chamber should be
determined with the highest possible accuracy. It is important
that the light intensity either remain constant throughout the
run or that it at least be well defined.
(d) Since the time required to reach the NC>2
peak and the amount of 0^ produced depends greatly on (NC^)0, it
is most important that the initial concentration of NC>2 in the
smog chamber runs be accurately determined.
(e) The experimental errors associated with each
measurement should be determined and reported. It is difficult
to assess the validity of a fit when the experimental uncertainties
are unknown.
(f) It would be of value to monitor nitric and
nitrous acid concentrations in future studies, if it is possible.
Determination of wall concentrations of these species would also be
desirable.
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(g) In order to assess chamber effects and to
determine the reproducibility of the experimental technique,
single hydrocarbon component systems should be studied. In order
to fine tune existing mechanisms and to determine synergistic
effects, it would be valuable to have accurate data for binary
mixtures of high and low reactivity hydrocarbons.
(h) Experiments to elucidate the role of aerosols,
the effects of mixing, and the effects of dilution would be of
benefit.
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3. Lowell G. Wayne - Pacific Environmental Services
L. Wayne stated that it is impossible to specify
the type of data needed for model validation unless one has a
clear idea of the purpose to be served by the model. He raised the
question of whether modeling is being done for its own sake -- to
prove that it can be done --or for the sake of establishing con-
trol strategy and emergency warning systems. What are the objectives
of modeling? Are we building a functional model or an aesthetic
one?
When aesthetic considerations dominate, the chemist
tends to become overly concerned with the accuracy of rate con-
stants while the non-chemist becomes overly concerned with tur-
bulence effects. As a chemist, Wayne desires to know as much as
possible about the elementary reactions and their rate constants
in order to have a complete and accurate mechanism. As a modeler,
however, he finds himself faced with the necessity of resorting
to lumped parameters, and the problem of determining how much
lumping can be done before a mechanism becomes too generalized to
serve its purpose.
If the model is to meet functional criteria, it
should be detailed enough to permit extrapolation with reasonable
confidence to ambient air quality concentration levels. To achieve
this, appreciable amounts of experimental data must become
available for these low concentration ranges or the mechanism
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must be detailed enough that varying concentrations will not affect
it. Both avenues should be explored.
For control strategy evaluation, it is more impor-
tant to have adequate chemistry built into a model than to have a
detailed accounting of the wind fluctuations. Wayne advocates
that the chemical mechanism be tested independently of the
meteorology through the analysis of smog chamber data. The vali-
dation of atmospheric simulation models by testing against
atmospheric data is a necessary step for generating confidence in
the model, but it is not an adequate procedure for authenticating
the chemical mechanism contained in the model.
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Discussion
J. Pitts commented on the new smog chamber research
facility under construction at the Statewide Air Pollution Research
Center and the efforts underway to establish a program to furnish
critically needed information. He urged the modelers to furnish
the smog chamber community with a list of priorities to aid them in
designing experiments. He especially wanted to know how much
emphasis should be placed on getting detailed product analysis.
Most of the participants felt that more complete
product analyses should be carried out in future studies.
K. Demerjian stated that measurements of methyl nitrate, HN03 and
^2^2' in Particular, would aid him in his modeling efforts.
A.P. Altshuller raised the point that collecting
atmospheric data is far more costly than performing smog chamber
irradiations. Therefore, any information that can be extrapolated
from controlled experiments should be obtained in this medium
rather than carrying out expensive atmospheric studies. He also
questioned the modelers as to how detailed a hydrocarbon analysis
of complex smog chamber mixtures is necessary. Due to the expense
and the experimental difficulties encountered in such analyses,
there is no point in carrying out exhaustive hydrocarbon analyses
if the modelers can't use them.
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B. Proposed Smog Chamber Study to Aid in the Modeling
Effort - Harvey Jeffries
H. Jeffries discussed a novel type of chamber study soon
to be initiated by L. Ripperton's group at the University of
North Carolina under EPA sponsorshop. This chamber facility is
being constructed out-of-doors in a rural community near Research
Triangle Park. The structure will consist of an A-frame, covered
with transparent Teflon film, that will be divided into two halves,
each with a volume of 6,000 cubic feet. Each half of the chamber
will be filled with the relatively clean rural air and then the
chambers will be charged with varying amounts of hydrocarbons and
NO . Irradiations will be carried out under conditions of natural
J\
sunlight, temperature, and humidity.
The experiments to be conducted in this outdoor chamber
are designed to furnish information on what effects a reduction
in ambient hydrocarbon levels will have on air quality. In the
coming years increased control of both mobile and stationary sources
will result in lower atmospheric levels of hydrocarbons. Some
evidence concerning the effect of hydrocarbon control on oxidant
exists. However, what effect reduced hydrocarbon levels will have
on the rate of formation of NC>2 is entirely unknown. There is
some evidence to suggest that, within certain ranges of HC and NOX
levels, a decrease in hydrocarbon level can lead to an increase
in NO2 formation.
To determine the effect of varying hydrocarbon levels on
N02 formation, experiments will be carried out by filling the
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27
chamber with the rural air and then injecting equal concentrations
of NOV into both sides of the chamber. Different concentrations
Jt
of a synthetic atmospheric hydrocarbon mixture will then be added
to each side. Since all conditions in both halves of the chamber
will be identical except for the hydrocarbon concentration, the
effect of the hydrocarbon level on the conversion of NO to N02,
the N02 maximum and the N02 dosage can be observed directly.
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28
C. The Role of Aerosols in Photochemical Smog - Arthur Levy
A. Levy discussed the research planned for the Battelle
smog chamber to furnish information on the role of aerosols in
photochemical smog formation. Battelle has just initiated a
program under EPA sponsorship to follow the number, size, and
volume distribution of aerosol particles produced in the smog
process. Previous smog chamber studies have been limited to defining
aerosols strictly in terms of light scattering. In the present
program, besides developing the standard smog parameters and light
scattering profiles, the growth and development of particles from
about .01 microns to possibly 10 microns in diameter will be
followed. Particle size distribution curves will be developed for
aerosols produced from specific hydrocarbon nitric oxide systems
as well as auto exhaust systems.
Previous work at Battelle showed that mechanical stirring
in the chamber significantly reduced the concentration of light
scattering aerosols. To study this effect in greater detail,
individual hydrocarbons (toluene and hexene) will be irradiated in
the chamber with and without S0~ and with and without stirring.
Also among the studies planned for the smog chamber is an
investigation of the inhibition of aerosol formation with hydrocarbon
mixtures. Prior work has indicated that the formation of light-
scattering aerosol may be markedly lower in systems composed of
certain mixtures of hydrocarbons. This was particularly apparent
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29
in a mixture containing several aromatics where considerably less
aerosol was produced than in a system containing a single aromatic.
Studies are planned to elucidate the chemistry responsible for
this effort.
Another anomaly that is under investigation is the fact
that considerably less light scattering is produced in smog
chambers than in the atmosphere. Likewise, eye irritation
measurements are generally lower in chamber studies than in the
polluted atmosphere. This latter effect may imply that photo-
chemically-produced aerosol is an eye irritant. Chamber studies
on auto exhaust samples are also planned to elucidate the effect
of primary aerosol on the formation of secondary aerosol. The
auto exhaust studies will be conducted with exhausts from leaded
as well as nonleaded fuels generated from cars that have been driven
only with the leaded or nonleaded fuels. Previous studies indicated
that the concentration of particulates present in auto exhaust is
an important variable affecting the formation of photochemical
aerosols. Studies will be carried out with varying particulate
loading of the auto exhaust samples to elucidate this effect.
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30
IV. THE ROLE OF ATMOSPHERIC MEASUREMENTS IN MODELING
A. Recommendations for Future Field Studies -
Alan Eschenroeder
A. Eschenroeder commented on the type of field measurements
he feels are needed to aid in the validation of photochemical
simulation models. Some of the suggestions he offered were:
1. Vertical profiles of temperature and concentration
should be obtained. All of the advanced air pollution simulation
models consider the effects of dispersion, horizontal advection
and vertical spread of pollutants. Ground-based monitoring
stations provide only a small part of the needed information.
The gathering of data in three dimensions is essential to the
validation of the models.
2. Current validation efforts are hindered by the
sparcity of hydrocarbon measurements, both in the number of
monitoring stations taking the measurements and in the frequency
of the readings. In future studies more measurements should be
taken even if it means trading off a few detailed analyses for
more frequent readings of only total and non-methane hydrocarbons
3. Results of the current GRC validation effort showed
that, while the observed build-up of CO and hydrocarbon during
morning peak traffic correlated well with literature values of
emission fluxes and atmospheric diffusion coefficients, the
build-up of NOX did not. Using the tabulated emission rates in the
model grossly overpredicted the early morning build-up of NOX.
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31
Due to an apparent heterogeneous uptake of nitrogen oxides, the
published values of emission rates had to be reduced by a factor
of four to offset the loss. This was consistent with the findings
of one other modeling group; however, the remaining two groups did
not find it necessary to adjust the tabulated NOX emission rates.
An effort should be made to identify the atmospheric removal
processes for the oxides of nitrogen so that appropriate sink
mechanisms can be incorporated into the models.
4. Another area of needed research is to ascertain the
influence of concentration inhomogenieties upon atmospheric rates
of reaction. Due to atmospheric turbulence and the incomplete
mixing of pollutants that results, nonuniformities in concentrations
arise. The most obvious effect of this turbulence is that the
equilibrium balance between NO and 63 can be upset. Simultaneous
chemiluminescence measurements of NO and 0^ taken at 4 a.m. in
New York showed that far higher readings of 0^ were obtained than
can be calculated on the basis of the NO/03/N02 equilibrium.
If this effect is real, using literature values of the rate constant
for the reaction of NO and Oj in simulation models may result
in an overestimation of the levels of N02 and an underestimation
of NO and Oj concentrations. The magnitude of this phenomenon
should be determined before carrying out extensive validation
efforts on time-averaged air quality data that may be invalid.
As a provisional measure, atmospheric samples could be drawn through
a multiple-inlet sampler equipped with a mixing chamber in order to
eliminate the effects of inhomogenieties.
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32
Discussion
Chemists and modelers took opposing views in regard
to the importance of turbulence effects. Most of the chemists
felt that Eschenroeder was magnifying the degree of non-mixedness
in the atmosphere and hence, the importance of its effect on the
chemistry. Many felt that this effect might be important at
ground level due to local sources, but that inhomogenieties should
not be as critical at higher altitudes. Eschenroeder made a plea
for strip charts of simultaneous 0, and NO readings so that he could
determine whether or not the turbulence effect was serious. At
the moment, he did not feel that enough evidence was available to
determine just how important this effect might be.
P. Roth made the statement that, in his modeling of
the Los Angeles data, he did not find it necessary to reduce the
emission rates of NO in order to describe the early morning
A.
build-up of oxides of nitrogen. He claimed that he obtained a
reasonable fit using the literature values of emission fluxes.
It was brought out that PES also could fit the observed build-up
of NOV without reducing the emissions, but that Systems, Science and
A.
Software, another concern engaged in model validation, could not
achieve a fit using tabulated emission fluxes. Eschenroeder re-
emphasized the need to carry out NOX loss studies to determine if
such an uptake of NOX is occurring on the atmosphere.
P. Roth added three more areas of inquiry to the list
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33
of topies for future investigations: 1) Aerosol characterization
studies followed by smog chamber studies of systems charged with
synthetically generated aerosols having the general characteristics
of atmospheric aerosols, 2) Identification and measurement of such
species as HNOs, HN02, H202, aldehydes and PAN, and 3) Studies to
ascertain the range of conditions under which the assumption of
the integrity of an air parcel is valid.
R. Martinez closed the discussion by re-emphasizing
the need for more measurements in order that further refinements
in the model may be made and that many of the points in debate
at this meeting could be solved. He re-emphasized the urgency to
obtain vertical concentration gradients, mixing depths and adequate
hydrocarbon measurements. He also emphasized the need to acquire
better rate constant data in order to reduce the degrees of
freedom in the chemical models and minimize the tendency to curve fit.
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34
B. Los Angeles Reactive Pollutant Study - William A. Perkins
W. Perkins commented on the atmospheric measurement program
planned for the Los Angeles Basin during the 1973 smog season. This
study is designed to furnish information on the fate of reactive
pollutants in the atmosphere. The undertaking is a joint effort by
the Coordinating Research Council and by the Chemistry and Physics
Laboratory and the Division of Meteorology.
The objective of this program is to provide a data base
suitable for developing and testing photochemical models. The
primary emphasis of this study will be on the gaseous reactive
pollutants. The basic concept of this program involves the premise
that a moving block of air can be identified and followed as it
moves downwind. Three tetroons will be launched simultaneously
to identify the air parcel. An atmospheric tracer, released from
an aircraft, will be used to indicate diffusion and vertical
movements. The air parcel will be tracked by two helicopters at
different altitudes and by a ground mobile unit. Aerometic
measurements will be made of 0^, NO, NC^, CO, non-methane HC, and
UV intensity. Bag samples will be collected for subsequent GC
analysis of the individual hydrocarbons. By following an air
parcel, rather than sampling from ground stations that see a
succession of air parcels with various ages of reactants, it is
anticipated that changes in the nature of the pollutants as they
undergo reactions can be observed directly.
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35
C. Coupling of the Photochemistry to an Airshed Model -
Ralph C. Sklarew
R. Sklarew of the Models Development
Branch in the Division of Meteorology
is project officer for the three
contracts in photochemical modeling.
R. Sklarew commented on some of the difficulties that
must be solved before the full potential of photochemical models
as predictive tools for the assessment of air quality can be
realized.
One of the problems of current concern is how to incorporate
the chemistry into the airshed models. The difficulties in coupling
photochemical mechanisms with the meteorological models stem from
the basic formulation of the two types of models under development.
These are the trajectory or moving coordinate models and the grid
or fixed coordinate models. The trajectory model focuses on a
volume of air that moves with local mean wind speed through the
airshed. Chemical reactions are simulated within this volume of
air. Source emissions are added as the volume flows over the
source. In essence, the trajectory can be viewed as a moving chamber
into the bottom of which pollutants are continually being injected
and inside of which chemical reactions are occurring. In this
system, the chemistry can be handled with almost as much ease as
in a static smog chamber. On the other hand, the grid type model
is formulated by subdividing the airshed into 3-dimensional
stationary cells and the polluted air is simulated as it passes from
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36
cell to cell. While the trajectory approach emphasizes the
natural reference frame in which chemical reactions are occurring,
the grid approach forces the reactions to be simulated in a
system that is not moving. Errors in following chemical reactions
in this stationary system can result. On the other hand, the
fixed reference frame of the grid model is the preferred one for
calculating the effects of diffusion and the contributions from
point sources. Currently efforts are underway to develop a hybrid
type of model using the best features of both the fixed and moving
coordinate approach.
Another difficulty that must be resolved is that, at
present, the effects of local point sources cannot be included
accurately in the models. Point sources are presently handled by
smearing the emissions over an entire grid. Because of this
smearing of pollutant concentrations over a wide area, the scale
of resolution of all of the models is poor. Efforts are currently
underway to determine means for handling localized concentrations
in order to improve spacial resolution.
Although the present accuracy of the models is limited,
the models can be used in their present form to simulate the relative
effects of control strategies. For example the models are currently
being used to evaluate proposed transportation control strategies.
The models are first used to simulate the observed pollutant levels
using present emissions. Then, the traffic control strategy is
translated into emission reductions and the photochemical model is
again used to simulate the pollutant levels after the control.
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37
Discussion
During the meeting several individuals indicated that they
did not have a clear idea of the objectives of the modeling program.
W. Perkins, in particular, asked what purpose EPA expects models
to serve. R. Papetti responded by stating that one of the main uses
EPA expects to make of its models is to assess the effects of alter-
native control strategies. Given a choice among several control
measures, models will be used to determine which one of the measures
should be adopted in order to achieve the greatest reduction in
pollutant levels. A major use of models will be to determine long-term
air pollution control strategies in terms of their economic impact.
Along these lines, models will be used by the states to aid them in
formulating their implementation plans. Another use of models will
be for land planning so that projected power plants and freeways may
be located where their air pollution is minimized. Another important
use of models will be to establish short-term strategies so that
impending air pollution episodes may be anticipated and consequently
prevented. Papetti also spoke of the possibility of using models
as a tool for predicting source signatures. Given a map of the
distribution of pollutants, it may be possible to use models to
identify the sources of these pollutants. It may also be possible to
use models to interpolate air quality between monitoring stations.
This interpolation could be both spatial and temporal. In essence,
modeling of this nature would fill out the picture, giving a far
more detailed description of a region's air quality than can be
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38
gotten from scattered monitoring stations. The last potential use
of models that Papetti mentioned would be to identify the impact
of major changes on air quality. An example of this use of models
would be to assess the result of new energy demands brought about
by large population growths or through changes in life styles.
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39
D. Summary
The proceedings of this modeling workshop illustrated the
fact that considerable resources are being expended by EPA to develop
photochemical models to assess air quality. The scale of the efforts
of both the Chemistry and Physics Laboratory and the Division of
Meteorology was apparent from the presentations and discussions that
took place in the two days. Many of the activities that the
Chemistry and Physics Laboratory is engaged in to elucidate the
chemistry of atmospheric transformation processes were discussed.
Descriptions were given of smog chamber studies at the University
of North Carolina and Battelle Memorial Institute, the Los Angeles
atmospheric measurement program, the St. Louis RAPS undertaking,
studies to define the role of aerosols, new instrumental techniques
to aid in the identification of trace contaminants, and the efforts
underway to employ these data to develop a photochemical mechanism.
The Division of Meteorology commented on their efforts to compile
emission inventories, air quality and meteorological data and to
develop numerical techniques to carry out computer simulations.
Many of the discussions were based on the efforts of their contractors
to model photochemical smog formation in the Los Angeles Basin.
The problems confronting the development of photochemical
models were explored during the two days. A set of chemical
reactions were reviewed and an assessment was made of the suspected
relevancy of each reaction in describing atmospheric transformation
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40
processes. In addition, those reactions for which the rates of
reaction are unknown or imprecisely determined and those reactions
for which the intermediates and products are unknown were determined.
Suggestions were offered on the type of smog chamber systems to
be studied, the measurements that should be made, the desired
accuracy of these measurements, the various chamber effects that
ought to be elucidated, and the reaction product species that ought
to be monitored. The paucity of atmospheric data available for
model validation were discussed and recommendations concerning the
types of measurements that should be made in future studies were
put forth. The many complex problems associated with the non-chemical
aspects of modeling were discussed. The many uncertainties in
emission inventories, meteorological variables and air quality data
were also explored.
It is hoped that these lengthy discussions were beneficial
to both the modeler and the chemist. Few problems were solved.
But problem solving was not the intent of this workshop. The intent
was to define the problems and to make recommendations for areas
where further research is needed. The recommendations that were
made during this workshop can be separated into these general areas:
1. Basic Chemistry
a. Obtain better means for determining ka0.
b. Determine the effects of surface-to-volume
ratio on the rates of formation of HNOj and HONO.
c. Determine rate constants for the reactions
of alkoxy radicals.
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41
d. Better determine the quantum yields of
aldehyde photolysis as a function of wavelength.
e. Determine the products of the reactions of
olefins with OH, 0, and Oj under atmospheric conditions.
2. Smog Chamber Experiments
a. Measurements of species should be made j.n_ situ
whenever possible.
b. Nitrogen balances should be obtained, if
possible.
c. Experiments should be carried out at concen-
trations approximating projected air quality levels.
d. Effects of aerosols should be studied by carrying
out chamber runs with varying particulate loading.
e. Careful control of light intensity, relative
humidity, temperature, and initial N02 concentration should be made.
f. The precision and accuracy of all measurements
should be reported.
g. More complete product identification and analysis,
especially for HNOj, MONO, H202, and PAN, should be made.
3. Atmospheric Measurements
a. Vertical concentrations and temperature profiles
should be obtained.
b. Mixing depths and wind speeds aloft should be
determined.
c. Atmospheric removal processes for NO should
be identified.
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42
d. The influence of concentration inhomogenieties
upon atmospheric rates of reaction should be determined.
e. Aerosol characterization studies should be made.
f. Detection in the atmosphere of such species as
HN03, HN02, and H202 should be made, if possible.
To achieve success in this modeling venture, it is imperative
that chemists and modelers work together. To ignore each others
expertise in his particular field of endeavor, to insist on a
duplication of efforts, or to stress one's own interests at the
exclusion of the other can only impede progress in this endeavor.
Better lines of communication between experimentalist and modelers
were established during this workshop and hopefully new impetus
to the modeling program will come about as a consequence of this
meeting.
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APPENDIX A
The Chemistry of Photochemical Smog Formation
2
3.
4.
5.
6.
7.
Reaction
N02 + hv -* NO + 0
0 '+ 02 + M + 03 * M
03 + NO -> 02 + N02
°3 + N02 "* N03 * °2
N03 + N02 n
NoOc -> N07
Z J w
N2°5 + H2°
N0
2HN0
8. N03 + NO * 2N02
9. N03 + hv -ť N02 + 0
10. NO + N02 + H20 -ť- 2HONO
11. 2HONO -ť NO + N02 + H20
12. MONO + hv -> OH + NO
13. OH + N02 + [M] -ť HN03 + [M]
14.
OH + NO + [M] -ť MONO + [M]
Comments
ka0 uncertain by ^20%; difficulties
encountered in trying to relate
measured kj to ka0.
Well known; k = 2.0 x 10'5 ppm"2 rain'1
20 4 k 4 40 ppm"1 min"1.
Two measured values, 0.11 and
0.048 ppm"1 min"1, both of which
may be too high.
kc and k^ uncertain by ^20%; equilibrium
constant is very temperature dependent.
Reaction in gas phase is negligible;
reaction occurs only on surfaces.
2
k factor of 10 uncertainty; most
important N03 removal process.
Importance not determined.
Rate may be higher than first order
with respect to H20; heterogeneous
contributions to this rate not
determined.
k12<%ť0.1 ka0; photolysis of MONO
in early morning may initiate smog
formation.
k uncertain; order of reaction depends
on pressure of M; probably second
order in atmosphere.
k uncertain; pressure dependence not
determined.
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A-2
Reaction
15. OH + CO ^ C02 + H
16. H + 02 + M -> H02 + M
17. H02 + NO * HO + N02
t
18. 2H02 -ť H202 + 02
19. H202 + hv -ť 20H
20. Paraffins + 0 -ť R + OH
21. Paraffins + OH -> R + H20
22. Olefins + 0 -ť ?
23. Olefins + OH -> ?
24. Olefins + 03 -ť Aldehyde
Zwitterion
25. Olefins + H20 * ?
26. Aromatics + 0 -ť- R + OH
27. Aromatics + OH + R + H20
28. RCHO + hv -> R + HCO
29. RCHO + hv + RH + CO
30. RCHO + OH -ť RCO + H20
31. RCHO + 0 -> RCO + OH
32. HCO + 02 -> H02 + CO
Comments
230 ^ k 4 280 ppm~ min" ; reaction
is too slow to compete with olefin - OH
reactions .
Only atmospheric reaction of
importance for H atoms .
102 4 k 4 103 ppm"1 min"1; most
important H02 removal process.
k uncertain by
Photolysis rate in sunlight not
well known.
k uncertain by ^ factor of ten.
k uncertain by ^ factor of ten.
k factor of 2 uncertainty; products
of reaction under atmospheric conditions
unknown .
Most important olefin reaction; products
of reaction unknown.
k factor of 2 uncertainty; reactions of
Zwitterion unknown.
Probably unimportant.
k's for most reactions unknown;
k26/- Do-
le's for most reactions unknown.
Quantum yields as function of hv
not well known; k2g may be an important
chain initiation step in atmosphere.
k iv 104 ppm^min'1.
Slow compared to Rx 30.
k high; only important HCO reaction.
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A-3
Reaction
33. RCO + 02 * RC(0)00
34. RC(0)00 + NO * R + C02 + N02
35. RC(0)00 + N02 -ť RC(0)OON02
36. R + 02 -* R02
37. R02 + NO + RO + N02
38. R02 + N02 -ť R02N02
39. R02 + H02 -ť ROOH + 02
40. RO + 02 -ť RCHO + H02
41. RO + NO f RONO
42. RO + N02 ť RON02
Connnents
Only RCO reaction of importance.
k unknown.
k unknown.
Very fast.
k unknown.
k unknown.
k unknown.
k unknown.
k unknown.
k unknown.
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APPENDIX B
Workshop Participants
Fred N. Alyea
General Electric Company
P.O. Box 8555
Philadelphia, Pennsylvania 19101
Theodore Baurer
General Electric Company
P.O. Box 8555
Philadelphia, Pennsylvania 19101
Joseph V. Behar
University of California
Statewide Air Pollution Research Center
Riverside, California 92505
James F. Black
Esso Research and Engineering Company
P.O. Box 51
Linden, New Jersey 07036
M. H. Bortner
General Electric Company
P.O. Box 8555
Philadelphia, Pennsylvania 19101
Raymond J. Campion
Esso Research and Engineering Company
P.O. Box 51
Linden, New Jersey 07036
David P. Chock
General Motors Research Laboratories
Fuel and Lubricants Department
Warren, Michigan 48090
Kenneth L. Demerjian
Ohio State University
Department of Chemistry
Columbus, Ohio 43210
Alan Eschenroeder
General Research Corporation
P.O. Box 3587
Santa Barbara, California 93105
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B-2
Donald L. Fox
University of North Carolina
School of Public Health
Chapel Hill, North Carolina 27514
William A. Glasson
General Motors Research Laboratories
Fuel and Lubricants Department
Warren, Michigan 48090
DavjLd M. Golden
Stanford Research Institute
333 Ravenswood Avenue
Menlo Park, California 94025
Thomas A. Hecht
California Institute of Technology
Spalding Laboratory 208-41
Pasadena, California 91109
Dale G. Hendry
Stanford Research Institute
333 Ravenswood Avenue
Menlo Park, California 94025
Harvey Jeffries
University of North Carolina
School of Public Health
Chapel Hill, North Carolina 27514
Harold S. Johnston
University of California
Department of Chemistry
Berkeley, California 94720
Richard Kamens
University of North Carolina
School of Public Health
Chapel Hill, North Carolina 27514
Arthur Levy
Battelle Memorial Institute
Atmospheric Chemistry and Combustion Systems Division
505 King Avenue
Columbus, Ohio 43201
Hiram Levy III
Astrophysical Observatory
60 Garden Street
Cambridge, Massachusetts 02138
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B-3
Alan C. Lloyd
University of California
Statewide Air Pollution Research Center
Riverside, California 92502
Jose R. Martinez
General Research Corporation
P.O. Box 3587
Santa Barbara, California 93105
Hiromi Niki
For'd Motor Company
Scientific Research Staff
Dearborn, Michigan 48121
William A. Perkins, Jr.
Metronics Associates, Inc.
3201 Porter Drive
Palo Alto, California 94304
James N. Pitts, Jr.
University of California
Statewide Air Pollution Research Center
Riverside, California 92502
Lyman A. Ripperton
University of North Carolina
School of Public Health
Chapel Hill, North Carolina 27514
Philip M. Roth
Systems Applications, Inc.
9418 Wilshire Blvd.
Beverly Hills, California 90212
Lowell G. Wayne
Pacific Environmental Services, Inc.
2932 Wilshire Blvd.
Santa Monica, California 90403
Karl Westberg
Aerospace Corporation
P.O. Box 95085
Los Angeles, California 90045
Environmental Protection Agency
Chemistry and Physics Laboratory
Research Triangle Park, North Carolina 27711
A.P. Altshuller
Joseph J. Bufalini
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B-4
EPA (continued)
Marijon M. Bufalini
Basil Dimitriades
Marcia Dodge
Alfred H. Ellison
Philip L. Hanst
Stanley L. Kopczynski
Charles F. Walters
William E. Wilson
Division of Meteorology
Research Triangle Park, North Carolina 27711
Warren B. Johnson
Francis Pooler, Jr.
Ralph C. Sklarew
EPA, Washington, D.C.
Robert Papetti
Processes and Effects Division
4th and M Streets
Washington, D.C. 20460
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