January 1973                            Environmental Monitoring
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


  on Mathematical  Modeling

    of Photochemical Smog :

Summary of the  Proceedings

            October 30-31, 1972

                Marcia C. Dodge

          Chemistry and Physics Laboratory
        National Environmental Research Center
     Research Triangle Park, North Carolina 27711
        National Environmental Research Center
                 January 1973

                         TABLE OF CONTENTS


    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

    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


    A.  The Modeling of Smog Chamber Data

        1.  Alan Eschenroeder	      19

        2.  Thomas A. Hecht	      21

        3.  Lowell G. Wayne	      23

        Discussion	      25

                              i i i


    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

    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


    The Chemistry of Photochemical Smog Formation 	      A-l


    Workshop Participants 	      B-l

                       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

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:



        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

            (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.


            (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.


    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,


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.


        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


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


    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


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


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.


    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


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.



                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

 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


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


        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


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,


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


    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.

    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
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.



    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


                (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.


                (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.


            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



                (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



            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


                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


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.



                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.


    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

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


chamber with the rural air and then injecting equal concentrations

of NOV into both sides of the chamber.  Different concentrations

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.


    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


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.



    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.


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.



            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

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

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


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.


    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.


    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


        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


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.



        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


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.


    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


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.


                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


                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


                c.  Atmospheric removal processes for NO  should

be identified.


                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


                                  APPENDIX A

                 The Chemistry of Photochemical Smog Formation





       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°
 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]
OH + NO + [M] -ť• MONO +  [M]
                               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.
                               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

                               k12<%ť0.1 ka0; photolysis of MONO
                               in early morning may initiate smog

                               k uncertain; order of  reaction  depends
                               on pressure of M; probably second
                               order in atmosphere.

                               k uncertain; pressure  dependence not

15.     OH + CO ^ C02 + H
16.     H + 02 + M -> H02 + M
17.    H02 + NO •* HO + N02

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

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

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.


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

Only RCO reaction  of  importance.

k unknown.

k unknown.

Very fast.

k unknown.

k unknown.

k unknown.

k unknown.

k unknown.

k unknown.

                            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


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


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


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