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


                              i i i

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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:




                               1

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                                2

        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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                                 8




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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                                14




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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                                15




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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                                16




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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                                18
    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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                                20




                (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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                                21




            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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                                22



                (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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                                23




            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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                                24




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.

-------
                                25




            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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                                26

    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

-------
                                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.

-------
                                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

-------
                                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

-------
                                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.

-------
                                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

-------
                                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.

-------
                                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

-------
                                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.

-------
                                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

-------
                                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.

-------
                                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.

-------
                                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.

-------
                                  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.

-------
                                      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.

-------
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

-------
                                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

-------
                                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

-------
                                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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