EPA - 450 / 2 - 75 - 005
July 1975


    CONTROL OF PHOTOCHEMICAL OXIDANTS-

                  TECHNICAL  BASIS

     AND IMPLICATIONS OF  RECENT  FINDINGS
             U.S. ENVIRONMENTAL PROTECTION AGENCY
                Office of Air and Waste Management
             Office of Air Quality Planning and Standards
             Research Triangle Park, North Carolina 27711

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                                 EPA -450/2-75-005
CONTROL OF PHOTOCHEMICAL OXIDANTS -

             TECHNICAL  BASIS

 AND  IMPLICATIONS OF  RECENT FINDINGS
        U.S. ENVIRONMENTAL PROTECTION AGENCY
            Office of Air and Waste Management
         Office of Air Quality Planning and Standards
        Research Triangle Park, North Carolina 27711


                  July 15, 1975

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                                 CONTENTS
                                                                   Page
LIST OF FIGURES	iii
LIST OF TABLES  	iii
SUMMARY	iv
INTRODUCTION	'	  1
EFFECTS OF OXIDANTS ON THE ENVIRONMENT AND THE
OXIDANT STANDARD	  2
FORMATION OF OXIDANTS IN THE ATMOSPHERE	  3
OXIDANT CONTROL STRATEGY	  8
    Federal Programs for Oxidant Control	  8
    State Programs for Oxidant Control    	  9
RECENT FINDINGS	12
    Recent Trends of Oxidant Concentrations	12
    Rural Oxidants	16
    Sources of Rural Oxidants	17
    Atmospheric Phenomena Which Affect Oxidant
    Concentration	18
    Assessment of Recent Technical Findings   	23
IMPLICATIONS OF RECENT FINDINGS FOR OXIDANT
CONTROL STRATEGIES   	27
    General Implications	27
    Implications for Control of Urban Oxidants	28
    Implications for Control of Non-Metropolitan Oxidants     	29
EPA PROGRAMS LEADING TO MORE EFFECTIVE CONTROL
STRATEGIES	32
REFERENCES	34
                                      11

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                            LIST  OF  FIGURES
Figure
  1     Photochemical Production of Oxidants	   4
  2     Results  of a Typical Smog  Chamber  Experiment	   5
  3     Southern California Oxidant Trends	   13
  4     Mean Diurnal Ozone Concentration at McHenry, Md.   	   15
  5     Hourly Averages  of Freon  11 and Ozone, Whiteface, New York   •  •   20
  6     Ozone Profile Flight,  Wilmington, Ohio,  August 1, 1974	21
  7     Smoothed Variations of Area Average Daily Ozone - Surface-
        Pressure - 1973 Time Sequence  	22
  8     Average Ozone Concentration 06 July  1974	24
  9     Average  Ozone Concentration 08 July 1974	25
                             LIST  OF  TABLES
                                                                        Page
        Simplified Summary of Chemical Reactions for Production of
        Oxidants	   4
  2     Ozone Data June 14 - August 31, 1974	  17
  3     Nationwide Hydrocarbon Emissions	  30
                                     111

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                                  SUMMARY
    As part of the Clean Air Act's mandate to protect public health and enhance the
environment,  the Environmental  Protection Agency has  developed a program to
attain and maintain the National Ambient Air  Quality  Standard for Photochemical
Oxidants.  This program requires the reduction in emissions to the atmosphere of
the precursor chemicals that are responsible for the formation of oxidants.  Control
measures have been instituted at  both the Federal and State level and include the
Federal  Motor Vehicles  Control  Program, the Federal  program for control of
aircraft emissions, development of Federal New Source Performance Standards for
stationary sources,  and those  measures  taken  by  the   States through State
Implementation Plans to attain the oxidant standard.  State measures include such
programs  as  control of  stationary  sources and Transportation Control Plans to
control in~use motor vehicles  and  reduce vehicular traffic  in urban areas.
    Oxidants are not emitted directly into the atmosphere but result primarily from
a  series  of  chemical  reactions  between  oxidant precursor compounds  in  the
presence of  sunlight.    The  precursors are  organic compounds  and  nitrogen
oxides,  primarily  emitted from motor vehicles and stationary sources.  Several
fundamental facts concerning  oxidant formation have been important in developing
a strategy to  reduce oxidant  concentrations.  These are:  (1) organic compounds
do  not all react at the same rate in the chemical process  and while  some react
within several  minutes, others  may take  many  hours;   (2) in addition to  the
absolute concentrations of precursors, the ratio of organic compounds  to nitrogen
oxides is important in  determining the  concentration of oxidants formed;  and (3)
meteorological  conditions,  such as sunlight ultra-violet intensity,  temperature,
and atmospheric stability affect  oxidant production.
    These considerations and  our knowledge of  the nature and  distribution of
precursor emissions form the basis  of EPA's  program  for  reducing  oxidant
concentrations  by  reducing emissions of organic compounds from  all significant
sources  through  the various Federal  and State  programs.  EPA also  requires
reductions in nitrogen  oxide  emissions  to meet the National Ambient Air Quality
Standard for nitrogen  dioxide, but does not  require  their  reduction in order to
control oxidant concentrations.
                                       IV

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    To insure the technical accuracy of the oxidant control strategy and to refine
that strategy where  necessary, EPA has conducted a  continuing program  of
research studies and  data analysis. New  findings based  on laboratory and field
studies accomplished  over the last several years  generally support the  control
measures currently being taken  and further indicate that additional measures may
be  necessary in order to meet  the oxidant standard nationwide.  These  recent
studies have documented frequent violations of the oxidant standard in both urban
and rural areas although,  in some urban areas, both the maximum concentrations
of oxidants and the  frequency of violations have decreased over the past several
years.  At  rural  locations, the number  of violations  of the standard  and the
maximum concentrations are sometimes as high and  even  higher than in  nearby
urban areas.  It is thus apparent that oxidants are a rural as well as an  urban
problem.
    The recent  studies show that:   (1) man-made emissions are the predominant
source of high levels of oxidants, even in  remote rural areas; (2) the contribution
of natural sources of oxidants  is usually not more than 0.05 ppm,  compared with
the oxidant  standard of  0.08 ppm;   and  (3)  transport  of oxidants  and  their
precursor compounds has been demonstrated to about 50 miles downwind of urban
areas and it is  likely that transport over longer distances occurs.   It also has been
shown that  the  highest oxidant  concentrations in the Midwest in both rural and
urban areas occur  during periods of stagnant conditions  associated  with high
pressure weather systems.
    In  both  urban  areas  and  in  many  non-urban  areas,  there  appear  to be
sufficient emissions of man-made precursors to account for the high oxidant levels
observed.   While transport of oxidants and  their precursors may occur, most
urban areas probably are responsible for their own  oxidant problem. The high
oxidant levels in non-urban areas appear  to be the  result of both locally produced
precursors and  precursors transported from urban  and other non-urban sources.
As  a  result, control strategies  for non-urban areas will  need to be directed  at
measures which reduce emissions  from both non-urban sources as well as  urban
sources and which meet the specific needs of each of these areas.

The following implications from the new findings are suggested:
     •   Continued application of  hydrocarbon control measures  in the urban
        area.  Because of  the  high  precursor emission densities  and the great
        numbers of people  exposed to oxidants, continued emphasis on intensive

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        control measures within  cities will be  necessary to meet the  oxidant
        standard in major urban areas .
     •  Increased  control over wide geographic areas through Federal and State
        programs  to meet  standards  in non-urban  areas.   In addition to the
        continued  intensive control of hydrocarbon emissions in urban areas, it
        may  be  necessary  to  extend  some  measures  under present  State
        Implementation Plans to include non-urban areas as well as cities.
     •  Increased  control of stationary sources.  Although mobile source controls
        (including Transportation Control Plans) will continue to be a major part
        of the oxidant control program, there is a need for more stringent control
        of precursor emissions from stationary sources.
     •  Increased  emphasis on  controlling all reactive organics.  Both under
        conditions  of  transport  and  under persistence of stagnant air masses
        there can  be sufficient time for less reactive hydrocarbons to contribute
        to  oxidant formation.  This indicates  the importance of controlling all
        organic compounds which can  form oxidants.
     •  Control of nitrogen oxides as  well  as hydrocarbon emissions may become
        necessary to meet  the oxidant standard  nationwide.    Nitrogen  oxides
        emissions  may be transported into rural areas and contribute to oxidant
        formation  by  reaction with locally emitted  organic  compounds.   It may
        eventually become necessary to  consider  control of nitrogen  oxides,
        coordinated with the control  of hydrocarbons,  as a part of the  oxidant
        control strategy.
     •  Emissions  from  natural  sources.   Oxidant  concentrations which can be
        attributed to natural sources  are usually less than 0.05 parts per million
        compared with the oxidant standard of 0.08 parts per million.  Because of
        emissions from natural sources, more stringent reductions of man-made
        emissions may be necessary in some areas.
    Further refinement of the oxidant  control strategy requires a more quantitative
understanding  of  the  chemical and the meteorological processes leading to high
oxidant concentrations.  EPA is engaged in an  extensive program of laboratory and
field studies to obtain the  needed information.   The program includes studies to
quantify the relationship between emissions of precursors and concentrations of
oxidants in the air  at both  urban and non-urban locations.  More extensive data
are being  obtained  on atmospheric levels  of oxidants and precursors as well as
                                       VI

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data on natural  and man-made precursor emissions.  It is expected that through
this  program  the current strategy will evolve over the next  several years  to
include the best measures needed to control oxidants in both urban and non-urban
areas.
                                     vn

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     CONTROL  OF  PHOTOCHEMICAL OXIDANTS  -

                       TECHNICAL  BASIS

      AND  IMPLICATIONS  OF  RECENT  FINDINGS



                           INTRODUCTION

    The strategy used by the Environmental Protection Agency for reducing the
concentrations of photochemical oxidants was largely formulated by 1972.  Although
the  strategy  has undergone some refinements,  it still retains the main features
developed at that time.  Laboratory and field studies over the last several years
have contributed much new information about oxidants.  While the understanding
of these new findings and of the overall oxidant problem is  not yet complete, the
new  findings generally  support  the  control measures  that are being  taken.
Furthermore, the accumulating base of data indicates that additional measures may
be needed in order to meet the oxidant standard nationwide.
    This paper discusses the current strategy and its technical basis. It reviews
the  recent findings  and discusses their  implications for further increasing the
effectiveness of the  strategy.  It identifies  the  topics  which  must be  better
understood before an optimum strategy can be developed and implemented,  and it
indicates  the study  programs  underway  or planned  to  provide  the needed
understanding.

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            EFFECTS  OF  OXIDANTS ON  THE ENVIRONMENT
                     AND THE  OXIDANT STANDARD

    Oxidants are strongly oxidizing compounds which are the primary  constituents
of photochemical smog.   The oxidant found in largest amounts is ozone, a very
reactive form of oxygen.  Oxidants also include the group of compounds referred to
collectively as PAN (peroxyacyl nitrates) and  other compounds produced in much
smaller  quantities.   The  most  accurate  technique  for  determining  oxidant
concentrations is  one that measures  ozone  rather  than total  oxidants.  This
measurement method (chemiluminescent) is the one recommended  by EPA and was
the method used to develop most of the data in this report.  Consequently, although
the term  oxidant is used often in the text, the discussion of measurements refer to
ozone values.

    Adverse  effects  on  human  health resulting from  exposures to  very  low
concentrations of oxidants have been  extensively documented for both man and
experimental animals  (Ref. 1, 2).  Also low levels of oxidants have adverse effects
on many  forms of vegetation and microorganisms and on materials  such as rubber,
cotton, nylon, and polyesters.  National Ambient  Air Quality Standards have been
established to protect human health  (the primary standard) and to  prevent adverse
welfare effects  (the secondary standard).  For oxidants,  both of these  standards
have been established at an ambient concentration of 0.08 parts per million (ppm)
which is equivalent to 160 micrograms per cubic meter (Mg/m ) This is  an hourly
average not to be exceeded more than once a year.

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           FORMATION  OF  OXIDANTS  IN  THE  ATMOSPHERE

    This  section presents the technical basis  for the approach used by  EPA to
control oxidants.  Oxidants are not emitted directly into the atmosphere but result
primarily from a series of chemical reactions between oxidant precursors (nitrogen
oxides and organic molecules) in the presence of sunlight. The principal sources
of organic compounds  are the hydrocarbon emissions  from automobile  and truck
exhausts,  gasoline vapors, paint solvent evaporation, open burning, dry cleaning
fluids,  and industrial operations.  There are also natural sources such as seepage
from  the  ground  and  emissions from  vegetation.  Nitrogen  oxides are  emitted
primarily from  combustion sources such as electric power generation units, gas
and oil-fired space heaters, and automobile, diesel and jet engines.  Nitric oxide
(NO)  is  the major  form  of  nitrogen  oxide  emitted  in  combustion  processes.
Nitrogen dioxide (NC^) is formed from NO and is the compound which decomposes
in sunlight to initiate the formation of ozone.
    The factors which determine the  concentrations  of  oxidants  formed in the
atmosphere include:    (1) the amount and kinds of  organic compounds initially
present and  the rate at which additional organics  are  emitted to the atmosphere;
(2) the amount  of nitrogen oxides initially present and their emission rates;  and
(3) sunlight ultra-violet intensity, temperature, and other meterological factors.
The interaction of these factors  and the  chemical reactions  involved are  very
complex and have been the subject of continuing scientific investigation during the
last 20  years, including atmospheric studies,  laboratory  smog  chamber studies,
and computer simulation of the oxidant forming process.
    A  large  number  of chemical reactions  that  may affect oxidant concentrations
are now known (Ref.  3,  4,  5) .    A  summary of the photochemical process  for
producing  oxidants is shown in Figure 1 and a simplified summary of the reactions
is presented in  Table 1.   In the oxidant forming process,  organic compounds are
oxidized to form peroxy  radicals and aldehyde  compounds.  The peroxy radicals
rapidly react with nitric  oxide (NO)  emissions to form nitrogen dioxide (NO2) • In
the  presence   of  ultra-violet  light  the   NO2 decomposes  back  to  NO  and

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PHOTOCHEMICAL
 BY-PRODUCTS
                                             FREE
                                           RADICALS
 ORGANIC
COMPOUNDS
         Figure 1.  Photochemical production of oxidants.
         TABLE 1. SIMPLIFIED SUMMARY OF CHEMICAL

           REACTIONS FOR PRODUCTION OF OXIDANTS

     •  OXIDATION OF ORGANIC COMPOUNDS TO FORM PEROXY RADICALS
                      02
        CH3CH = CH2+ OH'—VCH3CH2-0-0' + H2CO

            PROPYLENE     PEROXY RADICAL   FORMALDEHYDE

     •  ALDEHYDES + 02 + SUNLIGHT-*-ADDITIONAL PEROXY RADICALS

     •  PEROXY RADICALS CONVERT NO TO N02

        CH3CH2-0-0-+ NO -»-N02+ CH3 CH2-0-

        CH3CH2-0-+ 02-*-H02'+ CH3HCO ACETALDEHYDE
        UP TO FOUR CONVERSIONS FOR EACH CARBON ATOM

     •  OZONE FORMING REACTION

        N02+02 	^NO + Oi
              ULTRA-VIOLET

     •  OZONE SCAVENGING REACTION
        PHOTOCHEMICAL BY-PRODUCTS FORMED

        ALDEHYDES, PAN, AEROSOLS, NITRIC ACID, H202, OH', C02

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simultaneously forms ozone (O3) .  The NO2 can also react with the peroxy radicals
to form peroxyacyl nitrates (PAN) .  The importance of the organic compounds in
the process is to convert the NO to NO?- This reduces the concentration of the NO
molecules which react to destroy ozone and  also increases the concentration of the
MI>2 needed to produce ozone.  In the series of reactions that are possible, as many
as four molecules  of ozone can  be generated for each carbon atom in  the organic
molecules.
    Much  of  the  information  about  the oxidant  producing reactions  has  been
obtained from smog chamber experiments.  The results of a typical smog chamber
experiment are presented in Figure  2 (Ref.  6) .  These results show a  decrease in
the  reactive  hydrocarbon,  propylene,  as  the  aldehyde   compounds  and   the
oxidants, ozone and PAN,  are formed. The impact of the various reactions on the
nitrogen oxides leads to low levels of NO and a maximum in the  nitrogen  dioxide
concentration approximately one hour after the reactions start.
              0.54.
                                                trnVVACETYL NITRATE
                                               Pt--	(PAN)
                               120     180     240
                                  ELAPSED TIME (min)
360
           Figure 2. Results of a typical smog chamber experiment.  Irradiation of a
           propylene-NO-NOo mixture in air. Initial experimental conditions - 0.5
           ppm propylene, OA5 ppm NO, and 0.05 ppm NO2 in 760 torr of highly
           purified air.
    Several observations are related to this oxidant forming process. They are:
    1.  It  has been shown in smog chambers that organic compounds do not all
        react at the same  rate in the  photochemical process (Ref. 7).  However,

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given long irradiation times and sufficient  amounts of nitrogen oxides,
almost all  organic  compounds react to form  oxidants.   Very reactive
compounds  lead to high oxidant  levels within  a few  hours of their
emissions.   Less reactive compounds form oxidants over longer times and
may react as they move with an  air mass and thus contribute to observed
oxidant concentrations later in the day or far downwind of their source.
There are thousands of organic compounds in typical use.  Gasoline may
contain more than  two hundred  compounds whose composition will vary
by brand and by season of the year.  Since the organics emitted to the air
include  many  of these  compounds, there is an extensive variety of
reactions occurring in the atmosphere.
In the immediate vicinity of nitric  oxide  sources,such  as near power
plants and  highways,  relatively  little  ozone is  found.   Ozone reacts
rapidly with nitric oxide  and  is destroyed, but NO2  is formed.  In the
presence of sunlight, the NO2  can later react to form ozone again. These
interactions between ozone and the nitrogen oxides help explain several
observations.  Ozone  concentrations are usually  low at  night  in urban
areas because  the  NO emissions act to destroy ozone and the absence of
sunlight prevents additional ozone formation. City ozone  concentrations
are often lower than in adjacent suburban or rural areas because the NO
emissions  in  the  city   are  high  and  thus reduce  the  urban  ozone
concentrations.
In  addition to the  absolute  concentration  of  precursors  and  the
meteorological  factors,  such as sunlight and temperature, which directly
affect  the  concentration of  oxidants  formed,  the  ratio  of organic
compounds   to   nitrogen  oxides  is  important  in  determining  the
concentrations  of oxidants formed.  Smog chamber studies have shown
that both very high and low  ratios of  organic  compounds to nitrogen
oxide suppress the amount of oxidants formed (Ref. 8) . For intermediate
ratios, the  rate of formation  and  concentrations of oxidants  formed
depends on  the type  of  organic compound  and the ratio  of organic to
nitrogen oxide.  For most urban areas, the ratio of organic compounds to
nitrogen oxides in the atmosphere  is such  that reducing  the  ratio  will
help to reduce  the oxidant concentration.
The highest concentrations of  oxidants are most frequently observed in
the  afternoon  hours.  These  highest  levels of oxidants are  formed by

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reactions of the precursor organic compounds and nitrogen oxides that
were emitted earlier in the day or had accumulated from previous days.
Since  both  organics  and  nitrogen  oxides  are  removed  from  the
atmosphere   during   the   photochemical   reactions,   the   highest
concentrations  of these pollutants  are  thus usually observed during the
early morning hours at the start of the photochemical process.

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                    OXIDANT CONTROL STRATEGY

    On  the  basis of the knowledge and understanding  of oxidant formation pre-
sented above, EPA has approached the  control of photochemical oxidants  by re-
quiring the  reduction of atmospheric emissions of hydrocarbons  and other organic
compounds.    Although  a National  Ambient  Air  Quality   Standard  has  been
established  for hydrocarbons,  this standard serves only as  a guide for achieving
the oxidant standard and is not based on  health criteria.  Since methane is the most
naturally  abundant  and  the  most  unreactive  hydrocarbon species, only  non-
methane hydrocarbon compounds are specified in  the air quality standard.  This
standard is  0.24 ppm  (160 micrograms/cubic meter) for the  3-hour concentration
measured from 6 to 9 a.m. A National Ambient Air Quality Standard also has been
established  for  nitrogen  dioxide  (NO2) .  This standard is  based on the health
effects of nitrogen dioxide. Reductions in nitrogen oxide emissions are required to
meet this standard but are not required for the  control of oxidant  concentrations.

    The reductions in emissions of hydrocarbons and other organic  compounds are
to be achieved through Federal and State programs which have been formalized in
regulations  (Ref. 9) promulgated under the  Clean Air Act.  The Federal programs
provide  for the reduction  in  emissions nationwide  through the  Federal Motor
Vehicle Control Program, the  Federal program for control  of aircraft emissions,
and the development of New Source Performance Stadards.   The State programs
provide  for additional control measures  through  State Implementation Plans in
those areas  of the  country where  the Federal programs will not be  sufficient to
meet  the air quality standard for oxidants.  These programs are discussed in the
following sections.

FEDERAL PROGRAMS FOR OXIDANT CONTROL
    Because roughly half of  the hydrocarbons emitted to the ambient air in the
United States are attributable to motor  vehicles, a large portion of hydrocarbon
reduction is to  be  achieved  through the Federal Motor Vehicle Control Program.
This  program has required  progressively  stricter hydrocarbon controls  on all
light duty motor vehicles since the 1968 model year.   In 1970,  Section 202 of the
Clean Air Act required that hydrocarbon emissions from light  duty  vehicles and

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engines be reduced by at least 90% from emissions permissible in 1970 model year
vehicles.  This will eventually require emissions to be reduced to 0.41 grams per
mile.  Interim standards  of 1.5 grams  per mile  (g/m) are now required on 1975
through  1977 model year vehicles.  Regulations  also exist to limit hydrocarbon
emissions  from other  types  of  vehicles such  as  motorcycles,  trucks,  buses, and
aircraft.
    Section 111 of the Clean Air Act also authorizes EPA to promulgate "Standards of
Performance for New  Stationary Sources." These are standards for new sources
which reflect the best demonstrated system of emission control, taking the cost of
emission reduction into account.  New sources are sources which are constructed
or  modified after the standard has been proposed.  So far only one new source
performance standard has been promulgated for hydrocarbon reductions. This is
the standard for Storage Vessels  for Petroleum  Liquids  (March 8,  1974, Federal
Register).   There  are many  other hydrocarbon emitting  industrial operations
where standards of performance may be appropriate.  Some possible sources are
industrial  degreasing,  fabric  dry cleaning,  service station  gasoline  transfers,
automobile finishing  and other  industrial surface  coating  operations.  EPA  is
currently  studying  each of  these  areas  to gather background data.  Standards of
Performance for these sources are scheduled for promulgation between- 1976  and
1978.
STATE PROGRAMS FOR OXIDANT CONTROL
    Because  the  Federal programs will  not be sufficient to meet the oxidant
standard  in all locations,  each State  has been required  to  develop plans for
additional  reduction in  emissions  of organic compounds in those areas which will
not meet the oxidant standard.
    To assist States in preparing Implementation Plans, EPA published guidelines
in the August  14, 1971  Federal  Register entitled, "Requirements for Preparation,
Adoption  and  Submittal  of Implementation  Plans."  Twenty-seven States have
promulgated regulations  to reduce  hydrocarbon  emissions in some  portion of the
State.  In the other States, hydrocarbon regulations are left to local jurisdictions.
The State Implementation Plans  include  regulations for existing stationary sources
as well as  the  implementation, where necessary, of Transportation Control Plans.
    For the development of Implementation Plans, it is necessary to determine how
much the emissions  of hydrocarbons and other organics must be reduced.  It was
realized  that the relatively  simple methods  used for directly  emitted pollutants

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were not appropriate for the complex oxidant formation processes.  Therefore, an
attempt was made to quantify the amount of hydrocarbon reduction required to meet
the oxidant standard.   In  1970, the  data to relate non-methane hydrocarbon to
oxidant  concentrations  were  available   only  from  Denver,  Los   Angeles,
Philadelphia,  and  Washington, B.C.  The 6  to 9  a.m. average non-methane
hydrocarbon  concentrations   were  plotted against  the  peak  hourly  oxidant
concentrations observed later in the day at  the  same measurement sites (Ref. 10).
The points scattered because  of  the variations  in the  conditions which affect
oxidant formation.  A curved line was drawn to  enclose these data points within an
upper  boundary.   This upper  limit curve depicted  the highest  oxidant  levels
observed  for  a  given hydrocarbon concentration.  From this  curve the minimum
hydrocarbon reductions required to meet the oxidant standard could be calculated.
EPA published the result of this calculation as  Appendix J in the August 14,  1971
Federal Register.  Given  a measured maximum oxidant level in an urban area,
Appendix J is to be used to determine the amount of hydrocarbon control required
in that area.  In some cities the measured oxidant levels were  above (greater than
0.28 ppm)  the  applicable  range of Appendix J.  These cities were permitted to
reduce  hydrocarbon emissions proportional  to the  amount that oxidant  levels
exceeded the standard.
    Appendix B of  the August 14,  1971 Federal Register also gives emission
reductions which  are attainable through the application  of reasonably available
emission control technology.   These emission  limitations emphasize reduction of
total organic compound emissions, rather than substitution of less reactive organic
compounds,   because   of  the  evidence   that  few   organic   compounds  are
photo chemically unreactive.  For  organic  solvent  usage, however, such as in
surface coatings and dry cleaning, the guidelines present a list of low reactivity
compounds  that may be considered for exemption  for control.   At present only
fifteen States  have rules controlling emissions  from organic solvent usage. The
rules differ in detail from State to State, but most of the States have adopted rules
for organic solvents patterned after the Los  Angeles Rule 66 (Ref. 11) rather than
the Appendix B guidelines.  This rule defines  a group of photochemically highly
reactive compounds and regulates the emissions  of these defined compounds.
    Transportation Control Plans (Ref.  12) provide for reductions in hydrocarbon
emissions beyond  the  reductions achieved  by  the Federal Motor Vehicle Control
Program  and  stationary  source  regulations  set  forth  in   approved State
Implementation Plans.  Pollutant reductions are to be  achieved by such measures

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as decreases in vehicle miles traveled,  inspection  and maintenance programs,
retrofit emission  controls  for  certain  vehicles,  gasoline supply  limitation,  and
gasoline transfer vapor control.   There  are  currently  twenty-one  Air Quality
Control Regions which have transportation control plans for oxidant control.  The
compliance dates for six of these plans is May 31,  1975, while the other fifteen have
attainment dates between 1975 and May 31, 1977.
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                              RECENT  FINDINGS

    In  addition  to  the  control  measures being  taken  under  the  regulations
discussed  above, EPA and others have been  conducting field investigations and
laboratory studies to better understand the oxidant problem.  The recent studies
have  provided several new insights  and  strengthened the  understanding of the
oxidant formation process.   Oxidant monitoring at various locations has provided
data for determining concentration trends. Studies in  the  eastern United States
have  shown that the oxidant standard is often exceeded over large parts  of that
region and that oxidant concentrations in  rural areas  can be equal to or exceed
those  in  urban  areas.   The   studies   have  related the  observed   oxidant
concentrations  to atmospheric phenomena which  affect  oxidant formation and
transport  and to  the man-made  and natural  sources  of oxidants and their
precursors.  These  studies  and  phenomena are summarized and discussed in the
following sections.
RECENT TRENDS OF OXIDANT CONCENTRATIONS
    Hydrocarbon emissions in the  United  States reached  a  maximum  in  1968  and
have decreased by  about 7 percent between 1968 and 1972 as a result of emission
control measures.   At the same time nitrogen  oxides emissions have increased by
about 25 percent from 1968 to 1972 and had doubled  from I960 to 1970 (Ref. 13) .
Thus, in the typical urban  environment, both the hydrocarbon emissions and the
hydrocarbon to nitrogen oxide ratio has decreased.  The result  has  been that in
Los Angeles,  in urban  areas of New  Jersey, arid in other center  cities, both
oxidant  levels  and  the number of violations of the oxidant standard has decreased
(Ref.  14-16).  For  example, in  Los Angeles  and in  the New Jersey areas, the
number of days in  which the oxidant  standard has  been exceeded decreased more
than  50 percent  between  1965  and  1972. In smaller urban areas  of  southern
California, such as  Riverside,  Palm  Springs,  and Indio,  maximum  oxidant
concentrations have also decreased from 1971 through  1974 although the number of
violations  has  remained  high  (Ref.  17)  .  These trends  in maximum  oxidant
concentrations are  presented in Figure 3.  While these downward trends in oxidant
levels are generally typical,  there of course may  be  locations where levels have
not been decreasing.  The large increase in downtown Los Angeles for  1973 is
because of unusual meterological conditions.
                                        12

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1966
1968
1972
1974
 Figure 3.  Southern California oxidant trends.
                       13

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    Figure  4 shows how variable the year to year behavior of oxidant levels can
be.  This figure presents  the  average ozone  readings by  hour of the day for  a
rural site near McHenry, Maryland (Ref. 18) .  A possible reason for the variability
was  the  fact that frontal movements  recorded in  1973 were almost all  classified as
weak. Therefore,  they  may have lacked the vigorous vertical mixing  and flushing
action normally experienced during frontal passages.  This may help to explain the
generally higher ozone levels experienced in  1973 at McHenry relative to 1972 and
1974.
    A related  observation  is that ambient levels  of oxidant in urban areas are
sometimes higher on the weekends than during weekdays, even though traffic and
industrial emissions  are  presumably lower, particularly during the morning hours
on Sunday.  These results have been observed in a number of cities, including Los
Angeles, Indianapolis, and Linden, New Jersey (Ref. 19).
     The general observations  are that daily  average oxidant concentrations are
higher  on weekends and that,  in some cities, levels above 0.08 ppm occur more
frequently  on  weekend days than on weekdays.  However,  the highest oxidant
concentrations do not appear to occur as  frequently on weekends as on weekdays.
The  detailed  investigation of temporal and spatia]  distribution of  emissions,  the
meteorology,  and  chemical composition  of the air in the cities  has  not  yet been
accomplished in sufficient detail to fully explain  these observations.  As explained
below,  many factors may be  operating simultaneously to cause the higher weekend
oxidant  concentrations.   Because   these  factors  may  be  specific  to  weekend
behavior, the  observations of weekend oxidants  should not be construed  as a test
of oxidant strategy measures.  In urban  areas where reductions in  hydrocarbon
emissions have been  achieved,  long-term reduction in oxidant concentration has
occurred both  during the week  and on the weekends.
     Several important  observations  can be  made  about  the weekend oxidant
concentrations.  First, the air  entering or remaining in the city  on weekends may
contain  oxidants,  precursors,  and  partially  reacted intermediates  which have
persisted from earlier  days.  Secondly, detailed emission  inventories are  not
available to  completely specify the  differences  in emission  patterns  between
weekdays and weekends.  Saturday  driving patterns are  no doubt different from
weekday patterns, but automobile emissions in the total metropolitan areas may not
be significantly lower on Saturdays.  In industrial areas on Saturday and Sunday,
and  in  all urban areas on Sunday, it is likely that emissions of both hydrocarbons
and  nitric oxide (NO) are reduced considerably.  Thirdly, there are  data from Los
                                        14

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Angeles, urban New Jersey, and other cities to indicate that the ratio of NO to NC>2
is decreased on weekends.  The hydrocarbon to nitrogen oxide ratio also increases
on weekends.  These last observations  indicate that less NO may be available on
weekends to scavenge ozone molecules, and that N©2 concentrations,  which can
form  oxidant, may  have  endured  from  prior days.   Moreover,  the weekend
increase  in  the hydrocarbon  to  nitrogen  oxide  ratio cannot  be explained by
changes in traffic patterns alone.  Finally, aerosols have been  shown to be lower
on  weekends  and solar radiation higher with the possible impact that scavenging
reactions are  reduced and photochemical reactions increased.  The combination of
these interacting factors  results in the observations  of higher average weekend
oxidant concentrations.
RURAL OXIDANTS
    Prior to 1970, measurements of oxidants in rural areas were made infrequently
and did not indicate the presence of particularly high  concentrations.  But in the
course  of a   study  conducted by EPA  in  1970,  investigators  found  oxidant
concentrations in  a  rural area of western Maryland  and eastern West Virginia
which frequently exceeded  the national ambient air quality  standard during the
summer months.  Follow-up studies of increasing  magnitude were conducted in
1972, 1973, and 1974 (Ref. 18, 20, 21).  The most extensive measurements were
carried out in the summer of 1974 at widely separated sites in the eastern Midwest.
It was  found  that the oxidant standard was exceeded  on  a significant  number  of
days at both  urban and rural  sites. The  rural sites  exceeded the standard more
often than urban sites and  higher maximum concentrations were measured at the
rural locations.  Table 2  (Ref.  18) presents data on maximum ozone observed and
-frequency of  ozone above the standard of 0.08 ppm (160 micrograms/cubic meter) .
Note that at DuBois, a small city in rural  Pennsylvania, the oxidant standard was
exceeded 341  hours during the period June  14 to August 31,  1974.  During the
same period   at Pittsburgh, approximately 100 miles  southwest of DuBois, the
standard  was  exceeded  only   106  hours.  The  maximum hourly concentration
measured at DuBois was  0.20  ppm;  at  Pittsburgh it was 0.14 ppm.  Similar high
values  of ozone  have also been measured in rural areas of New York, New Jersey,
Wisconsin, and Florida  (Ref.  22).  It thus  appears that  in  many  areas of the
eastern United States high  concentrations of oxidants are found in both rural and
urban areas.
                                         16

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                 TABLE 2. OZONE DATA JUNE 14 - AUGUST 31, 1974
CITY
MAXIMUM
CONCENTRATION
(ppm)
DAYS
EXCEEDING
STANDARD
(%)
NUMBER
OF
VIOLATIONS
(TOTAL)
RURAL
WILMINGTON, OH.
MCCONNELSVILLE, OH.
WOOSTER, OH.
MCHENRY, MD.
DUBOIS, PA.
0.18
0.16
0.17
0.17
0.20
58
56
55
43
54
259 HOURS
239 HOURS
262 HOURS
262 HOURS
341 HOURS
                                             URBAN
CINCINNATI, OH.
DAYTON, OH.
COLUMBUS, OH.
CANTON, OH.
CLEVELAND, OH.
PITTSBURGH, PA.
0.18
0.13
0.15
0.14
0,14
0.15
44
35
27
44
26
37
54 HOURS
114 HOURS
113 HOURS
148 HOURS
51 HOURS
106 HOURS
SOURCES OF RURAL OXIDANTS
    There are several possible sources of rural oxidants that must be considered
in efforts to account for  the observed concentrations.  These sources include the
large quantities of man-made precursors that are emitted in urban areas and which
may  move into rural areas while reacting to form oxidants, as well as oxidants
formed from man-made precursors which originate in the non-urban areas. There
are also two possible natural sources of rural oxidants.  These are (1) downward
transport from the ozone-rich layers in the stratosphere into  the lower troposphere
near the surface,  and (2) photochemical generation from hydrocarbons emitted by
vegetation.   The available evidence strongly indicates that frequent and persistent
concentrations of ozone near the surface above the oxidant air quality standard of
0.08 ppm are not caused solely by natural sources and that the background that
can be attributed to natural sources is usually less than 0.05  ppm.
    The amount of ozone  transported from the stratosphere may  be estimated from
the numerous vertical ozone soundings  of the atmosphere made in past years (Ref.
23) .  These  generally show  ozone  concentrations at  a maximum in the lower
                                        17

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stratosphere decreasing to very low levels at or near the tropopause and with a
slight decrease downward toward the surface.  Ozone levels near the surface that
appear to be largely of stratospheric origin may at times range ifrom 0.03 to 0.05
ppm. Temporary higher readings, however, are possible with unusually deep and
vigorous   vertical  mixing  induced   by  strong   cold   fronts,  jet  streams,
thunderstorms, or some combination of these.  These are sporadic,  usually short-
lived events lasting on the order of minutes or, less often, a few hours.  Lightning
from thunderstorms  may also cause brief rises in ozone,  but  lightning by itself is
considered an insignificant contributor to the ozone levels observed in rural areas
(Ref. 24).
    The  natural  organic  compounds  emitted by  vegetation  may  react to  form
additional ozone or they may sometimes decrease it by scavenging reactions. The
ozone added by reactions of natural hydrocarbons may increase the ambient ozone
by  0.02  to 0.05 ppm  (Ref.  25).  However,  the atmospheric conditions that  are
conducive  to ozone  production  by the photochemical process  are not  usually  the
same conditions associated with transport from the stratosphere.  Therefore,  the
high values  of non-urban ozone that are frequently above the standard cannot be
attributed only to  natural sources, but rather,  they appear to be primarily of man-
made origin.  The  evidence for  this  conclusion  is  presented in  the  following
section.
ATMOSPHERIC  PHENOMENA WHICH AFFECT OXIDANT CONCENTRATION
    Recent measurements  downwind of urban centers (Houston,  Phoenix, several
Ohio  cities,  and  Philadelphia)  demonstrate that an identifiable urban  plume of
oxidants and oxidant precursors  travels as  far as  30-50 miles from the urban
center  (Ref.  18,  26, 27).  In Los  Angeles, where the magnitude of oxidant
generation is greater,  the distance can be extended to 75 miles or more downwind
(Ref. 28).  Beyond these distances, the individual urban  contribution of pollutants
becomes  so mixed  with   other  urban and  non-urban  contributions  that  the
individual urban effect is  difficult to distinguish. Therefore, while the  transport
of oxidants can partially explain the high oxidant levels at short  ranges downwind
of urban centers, it  has  been  difficult to  show definitely that  transport is  the
principle cause of high  readings at more remote sites.   However, as described
below,   there  is  new  evidence  that oxidants  and  their  precursors  can  be
transported over longer distances.
    To  date, the most positive  method  for  demonstrating  that the  high  ozone
concentrations observed at more remote locations  are at least  partially due to
                                        18

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emissions from man-made sources is by simultaneous measurements of ozone and
compounds that are only  emitted by human activity.  Freon 11 is such a compound
since it has no natural sources, is very stable in the lower atmosphere and has a
measurable   but   slowly   increasing  global   background  concentration  of
approximately  90  parts  per  trillion.   An  increase  above this  background
concentration is strong evidence for transport  of air  from areas of human activity.
In studies during 1973  and 1974 at Whiteface Mountain,  New York,  at Elkton,
Missouri, and  in  the Pacific Ocean  between Seattle  and San  Diego,  no levels of
ozone  above 0.08 ppm have been found in which Freon 11 levels were not  also
above  the background.  Figure 5 presents ozone and  Freon  11 measurements at
Whiteface Mountain from July 24-27, 1974 (Ref. 25).  On July  24 ozone moved into
the study area at  3 to 4 a.m. accompanied  by an elevated Freon 11 level.  July 25
was  heavily  overcast and there was  little  ozone  formation.  July 26  was sunny,
Freon   11  was  at  normal  background concentrations,  and there   was  ozone
production to 0.05 ppm during  the day.  On  July  27  there were elevated Freon 11
concentrations,  so  that  the  ozone concentrations may have been  due to  local
production and to ozone or precursors transported to the area. Thus, the higher
levels  of ozone measured on July 24 and July 27 are associated with high Freon 11
levels, which  implies  that these pockets of air had  been  transported from some
area where man-made emission sources are present.
    Certain meteorological phenomena may also help  explain the high rural ozone
concentrations.   Figure  6 presents  vertical ozone profiles taken at  three times
during one  day  during  the 1974 summer  studies  (Ref.  18).  These  profiles are
similar  to  other  vertical  measurements   reported by  other  observers  over
Indianapolis  and Canton, Ohio and are consistent with ozone soundings of previous
years.  The  concentrations of ozone decrease above the subsidence inversion near
8000  feet as shown by the temperature  profiles.  The  early  morning  profile
indicates  low ozone concentrations  (0.02 ppm) beneath  a radiation inversion  that
occurred  between  the   surface  and  2000  feet.   Trapped  between  these  two
inversions is a layer of ozone above 0.09 ppm  which had formed on previous days
and had persisted through the night.  In this layer, ozone has been separated from
ground based scavenger pollutants and  may persist  for long  periods  of time  and
may  be  transported over  long  distances.   At the  surface below the radiation
inversion, ground emissions of natural destructive  agents and  surface features
provide a sink  for the ozone. During the day,  as  the low level radiation inversion
layer dissipates,  the lower atmosphere becomes well mixed and oxidant, formed by
                                       19

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          Figure 5.  Hourly averages of Freon 11  and Ozone,

          Whiteface, New York.
                                  20

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             Figure 6.  Ozone profile flight, Wilmington, Ohio, August 1, 1974.
photochemistry from  precursors emitted at the surface or from hydrocarbons left
over  from the previous day,  mixes  with the  layer  of  ozone that had persisted
through the  night.  As the day progresses , more oxidant is formed  as shown by the
high  oxidant  concentrations measured in the afternoon.  This  typical  pattern
explains the usual diurnal oxidant concentrations measured at ground based rural
monitors.  This pattern usually shows low concentrations at night with build-up to
high  concentrations  in  the  afternoon.   Exceptions occur  when  high  oxidant
concentrations  have  been measured  at night  under atmospheric conditions that
dissipate or  prevent formation of the surface-based inversion.
    Preliminary analysis  of  data from the 1974 summer studies indicates that ozone
concentration variation also  is associated with large scale weather features related
to high pressure  weather systems (Ref. 18) .  Figure 7 presents a smoothed  graph
                                        21

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                                      22

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of surface  pressure  and surface ozone  concentrations  for 1973  averaged over
several  eastern study  sites.   This shows  that  the  highest  oxidant  readings
occurred during periods of high pressure;  however  as explained below, high
pressure in itself does not lead to high ozone.
    On a spatial basis,  the higher ozone concentrations generally seem to occur
near the central portion of high  pressure cells and decrease outward.  The spatial
distribution of ozone in  a high pressure system is shown on weather maps for July
6 and  July  8,  1974  in Figure 8 and Figure 9  (Ref. 18).  These are two of several
cases studied.  The five numbers in large boxes are the 8-hour afternoon averages
of ozone concentrations in parts per million observed at the rural monitoring sites.
The  six  numbers in smaller boxes are the ozone concentrations at urban locations.
The  contour lines are lines of constant pressure.  The center of the high pressure
system is  over Cleveland on July  6 (Figure 8)  and is  indicated by the  line
numbered 22  (1022  millibars) .  On  July  8 (Figure  9) the high pressure cell is
centered over western Pennsylvania.  The wind direction and velocity is shown by
the arrows.  The shading indicates areas of high man-rnade hydrocarbon emissions
where emission densities are greater than 10 tons  per square mile per year.  In the
urban  areas emission densities are between 100 and 1000 tons per square mile per
year.  Emission densities are high  in most  of this region and are sufficient to
account  for  the measured ozone  concentrations.  The evidence suggests that near
the  center  of  a high pressure  area, perhaps 100-200 miles in  diameter, envi-
ronmental conditions are most conducive  to high oxidant build-up.  Apparently,
near the center of  the high  pressure area,  there are  light disorganized winds,
sufficient ultra-violet radiation and high  temperatures as well as sufficiently high
emissions of  precursor  compounds.  Thus,  in  a slow  moving  high, a  virtual
outdoor  smog chamber develops in which locally generated oxidants are added to
oxidants and  precursors which  may have been  transported into the area as the
high pressure cell •was developing.
ASSESSMENT OF RECENT  TECHNICAL FINDINGS
    The  recent field investigations and laboratory studies of oxidant formation and
control have provided several new insights. It is now apparent that oxidants are a
rural as  well as an urban problem.  Oxidants can  be formed over  long time periods
during  stagnant conditions  in  high pressure systems  or during  transport of
oxidants and precursors.  This implies that the long-term behavior  of oxidants and
precursors  is an important contributor to oxidant concentrations.  It also implies
                                       23

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           1. AVERAGE DAYLIGHT OZONE CONCENTRATION
             (1200 TO 2000 EOT) IN PPM

             A.  SMALL BOX - URBAN
             B.  LARGE BOX -RURAL

           2. SURFACE PRESSURE (1700 EOT) IN MILLIBARS

           3. 24-HOUR RESULTANT SURFACE WINDS

           4. HYDROCARBON EMISSION DENSITY (> 10 tons/
             year-sq. mile) (SCREENED AREA)
Figure 8. Average ozone concentration 06 July 1974.
                        24

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     1.  AVERAGE DAYLIGHT OZONE CONCENTRATION
        (1200 TO 2000 EOT) IN PPM

        A. SMALL BOX- URBAN
        B. LARGE BOX - RURAL

     2.  SURFACE PRESSURE (1700 EOT) IN MILLIBARS

     3.  24-HOUR RESULTANT SURFACE WINDS

     4.  HYDROCARBON EMISSION DENSITY ( > 10 tons/
        year-sq. mile) (SCREENED AREA)
Figure 9.  Average ozone concentration 08 July 1974.
                      25

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that  less reactive organic compounds as well as the more reactive compounds can
contribute  to observed oxidant levels.  There are also natural sources of oxidants
which  at times may contribute to oxidant concentrations reaching levels near the
oxidant standard.  The studies indicate that man-made  emissions of hydrocarbons
are, however, the predominant source of the highest levels of oxidant.
                                        26

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                 IMPLICATIONS OF RECENT  FINDINGS
                 FOR OXIDANT  CONTROL  STRATEGIES
    Recent trends indicate that  the  current  strategy is leading to reduction in
oxidant levels in urban  areas.  However, it appears that measures in addition to
those planned under the current strategy will  need to  be  developed in order to
achieve  the  oxidant  standard  nationwide.    The  implications  suggested  are
discussed in detail in the following sections.
GENERAL IMPLICATIONS
    It is clear that high  oxidant levels are a problem in many non-urban as well as
urban  areas.  The large cities and major  urban areas are, of course, concentrated
major  sources of organic  compounds  and nitrogen oxides.  However, non-urban
areas also generate  substantial man-made precursor emissions.  These areas are
not necessarily rural, but may include many  medium and smaller sized cities that
may account for significant fractions of population. In the state  of Ohio, where the
rural oxidant studies discussed in the preceding  section were largely conducted,
the ten largest cities (population greater than 100,000)  account for approximately
60  percent  of the  total  man-generated hydrocarbon  emissions.   This leaves 40
percent of these emissions coming from the non-metropolitan areas of the state. It
would  follow then that the major steps needed to control oxidants in both urban and
non-urban areas are those measures  that effectively reduce the emissions in each
of these areas and which  take into account the individual  characteristics of each
area.  These findings in no way indicate that there should be  less control  of the
urban fraction of hydrocarbons .

    It will, of course, be necessary to consider the interaction  of  urban and non-
urban   areas  since   transport  of  oxidants   and  their  precursors occurs.  As
discussed in the previous  section, there is evidence that transport can take place.
The highest oxidant levels in both urban and  non-urban locations of the eastern
U.S. ,  however, appear  to occur within  areas  of a high pressure system.  Since
winds  are usually light  within  these  systems,  transport beyond about fifty miles
may not be important under these  conditions.  This would  support a view  that
within  high pressure systems the  urban centers  and the non-metropolitan  areas
are both principal contributors to their own oxidant problems.
                                      27

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    Because  controlling  urban  and  non-metropolitan  oxidants  may  present
different problems they  are  discussed under  separate  headings in the following
sections.
IMPLICATIONS FOR CONTROL OF URBAN  OXIDANTS
    Most  urban  areas are characterized by a large population at  risk and high
precursor emission  densities.   The  oxidant problem in these metropolitan areas
can be largely attributed to those mobile and stationary source emissions generated
within  the  community itself.  Based on recent  studies in  the  Midwest,  this is
particularly true during meteorological conditions characterized by stagnant high
pressure  systems,  the  same conditions during which  the highest  oxidant  levels
have  been  observed.  For these  reasons,  the continued application  of intensive
control measures in our urban areas is essential if we are to attain the oxidant
standard and prevent adverse effects  to human health.
    Of particular importance  in  achieving this  objective  are those  measures
designed  to  reduce  mobile  source  emissions.  Estimates  for  several  major
metropolitan areas show  that as much as 70 percent of total urban hydrocarbon
emissions are attributable to light  and heavy duty vehicles.  To effectively handle
this problem, continued emphasis will be required on Transportation Control Plans
to augment the Federal Motor Vehicle  Emission Control program.  These plans are
a key element in achieving the  oxidant  standard in urban areas and offer the only
viable approach to  achieving mobile source emissions reductions  beyond  those
resulting from the Federal Motor Vehicle Emission programs .
    Although  the   present   strategy  recommends   controlling   all  reactive
hydrocarbons or organic compounds,  it  does provide for substitution  of less
reactive for moderate and highly reactive materials where reduction of all organics
is not feasible or economic.  Within  large  cities  this approach can contribute to
reduced oxidant  levels,   and it  may be necessary to continue to permit  these
substitutions  where  measures for total hydrocarbon reduction are  not practical.
However, recent findings suggest that the  less reactive hydrocarbons within  an
urban area  can persist from one day to the next under stagnant conditions and thus
have  time to react and contribute  to oxidant levels.  Also,  under conditions when
transport of oxidants and precursors occurs,  there  can be sufficient  time for the
less  reactive organics  to contribute  to  oxidant levels in  neighboring  areas.
Therefore, while continued use of reactivity oriented measures  can be of value to a
city,  the recent  findings  place increased  emphasis on the need  to  control  all
organic compounds that can participate in oxidant  formation.
                                        28

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    Another implication  concerns  the  ultimate  need to control nitrogen oxides
emissions as part of the strategy for achieving the oxidant standard.  The oxidant
strategy relies on reduction of hydrocarbon emissions to meet this objective.  Our
understanding of the underlying chemistry continues to indicate that emphasizing
hydrocarbon control is the most effective way to  reduce the high levels of oxidants
seen in major urban  areas.  However,  this strategy can  leave unreacted nitrogen
oxides in the  atmosphere which  may be transported into suburban and rural areas
to  interact  with  further  infusions   of  organic  material  and give  oxidant
concentrations which  exceed  the standard in these  areas.   The observation  of
elevated weekend oxidant  levels in some cities may also be  related to varying
relative rates  of organic and nitrogen oxides emissions.
    The strategy leading to control of oxidants in urban, suburban, and rural
areas  will  continue  to  be  based on the  reduction  of organic  compounds.
Eventually,  however, as  oxidant levels are  reduced toward the standard, it  is
likely  that  coordinated  reductions  of  both organics and nitrogen oxides will be
required. In  a  coordinated  approach,  cities could take advantage of the beneficial
effect of a low organic to nitrogen oxides ratio while sufficient control of nitrogen
oxides  would  be necessary to  control oxidant formation downwind or during
extended stagnation conditions.

IMPLICATIONS FOR CONTROL OF  NON-METROPOLITAN OXIDANTS
    Non-metropolitan  areas, in contrast to  the  major urban  centers, have their
emission sources  spread over wide geographic areas.  Control measures that need
to be  taken  must be  effective  over   these  broad areas.  The Federal control
programs for  mobile and  stationary sources  apply nationwide and therefore have
this character.  The States  can  also extend their hydrocarbon control regulations
statewide.  These regulations  now tend to  be  confined to major urban areas within
the  States.    Through  the  State Implementation  Plans,  further  reductions  in
emissions can  be achieved from  both stationary  and  mobile sources  in  non-
metropolitan areas that  have an oxidant problem.  Thus, in the future,  it may be
determined  that certain States need to  adopt  statewide stationary source controls
and  possibly  certain  transportation   measures such   as  vehicle  inspection/-
maintenance.  This latter measure employed throughout  a State would help assure
maximum effectiveness of the Federal Motor Vehicle Control Program.
    To characterize the  need for stationary source control, a preliminary estimate
can be  made of the effectiveness of Federal programs in  reducing oxidants in the

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non-urban  areas  throughout  the  U.   S.   under  present  nationwide  control
timetables.  Table 3 shows estimates of national emissions of hydrocarbons from
various mobile sources and from stationary sources projected through 1985.  These
estimates  include factors  for expected  growth  in each category and  reductions
based on Federal programs now being implemented or required in the near future.
In the  case of  light  duty vehicles the estimates are  based  on  EPA's  recent
recommendations on extension of interim and statutory standards.  For the  mobile
sources, the retirement of older vehicles and the projected deterioration of control
devices is also included.

 TABLE 3.  NATIONWIDE HYDROCARBON EMISSIONS (MILLIONS OF TONS PER YEAR)
YEAR
1972
1975
1985
LIGHT-DUTY
VEHICLES
10.3
9.1
3.6
LIGHT-DUTY
TRUCKS
2.0
1.7
1.3
HEAVY-DUTY
VEHICLES
2.4
2.2
2.1
OTHER
MOBILE
SOURCES*
1.9
2.2
3.4
TOTAL
MOBILE
SOURCES
16.6
15.2
10.4
STATIONARY
SOURCES
12.5
13.7
14.7
TOTAL HC
EMISSIONS
29.1
28.9
25.1
 'AIRCRAFT, VESSELS, OFF-HIGHWAY, RAIL
    Since rural oxidant levels in excess of 0.16 ppm have been measured as was
reported in  Table 2  and natural background  concentrations  of  0.04 ppm and
possibly higher may occur, it is possible that  at least  a two-thirds reduction in
man-made  oxidants will  be  needed  to meet the oxidants  standard in some non-
urban regions.  Assuming that  the  relative reductions in nationwide  emissions
shown in  Table 3  approximate the  effect  of  the  Federal programs over broad
geographic areas,  it is not likely that they will be sufficient to achieve the needed
oxidant reductions. It appears from the above estimates that more needs to be done
than  is currently planned to solve the  non-urban problem.  Although  it may  be
possible to improve the controls for heavy duty vehicle emissions and other mobile
sources, the most promising area for achieving the broad  area  control needed for
non-urban areas would  appear  to be stationary sources.  In 1972 these sources
accounted for less  than half of the total emissions nationwide whereas by 1985 they
will account  for almost two-thirds of the  nationwide hydrocarbon emissions. This
distribution  may  not  be true  in  some rural  areas  where  motor  vehicles  could
remain the dominant source of emissions.
     The recent findings  have additional implications for control of the non-urban
 oxidants problem.  Both the more reactive and the less reactive organics, under
 the  conditions  of  light winds associated  with  persistent high  pressure systems,
                                       30

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may have sufficient time to generate oxidants.  Thus, reduction of total emissions
and  not  just  reduction  of  the more  reactive  compounds  would  need  to  be
emphasized in non-urban  areas. Control of organic rather than nitrogen oxides
emissions appears  to be the most effective route to reduce oxidant levels  in rural
areas.  However, to attain the standard, coordination of both organic and nitrogen
oxides emissions control may be necessary.
    Finally,  consideration of natural contributions of oxidants and precursors is
likely to be an important consideration in non-urban areas.  While recent  findings
suggest that  natural sources do not in themselves  lead to oxidant levels above the
standard,  they may in combination with man-made emissions  lead  to levels in
excess of the standard.  Therefore, stricter controls on the man-made emissions
may be needed to  compensate for the contributions from natural sources.  It may
also be found that the natural source contribution is sufficiently high in some areas
that  small additions  of  man-made  emissions  may  cause  the  standards  to  be
exceeded. In  these cases it will still be possible  to significantly reduce oxidants
but it may not be possible to attain the standards at all times and places.
    The implications of the recent findings for the control of oxidants  in both
urban  and non-urban  areas may be summarized as:  most organic compounds need
to be controlled; eventually the  coordinated control of both organics and nitrogen
oxides  may  be necessary;  present regulations need  to be expanded into non-
metropolitan  areas;  continued emphasis  on  mobile sources must be supplemented
by reductions in stationary sources; and natural sources should be considered in
determining required emissions reduction measures.
                                      31

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                             EPA PROGRAMS
        LEADING TO  MORE  EFFECTIVE CONTROL  STRATEGIES
    Substantial progress has been made in the last several years in understanding
the occurrence and formation of photochemical oxidants in the atmosphere.  It is
apparent from  all the  available information that the reduction in  emissions of
organic compounds will lead to reduction of oxidant  concentrations.  The recent
studies indicate  that additional measures  will be  needed in  order  to  meet the
standard everywhere.  There is still not sufficient information, however, to define
exactly what  control measures  will  be  needed to  meet the  oxidant  standard
everywhere.  EPA  is sponsoring an  extensive program of laboratory and  field
studies,  including development of improved mathematical modeling techniques , to
obtain the needed information.  The studies will:
    •   Determine  and quantify  the effect  of  intermediate  and   long-range
        transport on oxidant levels in both urban and rural areas.
    •   Quantify the  role of local emissions  of hydrocarbons and nitrogen oxides
        on the generation of rural and urban oxiclants.
    •   Determine the  long-term behavior  of oxidant  levels  in air masses in
        which   oxidant precursors  are  being  intermittently  or   continually
        injected.
    •   Quantify the  relative   roles  of  hydrocarbons  and nitrogen  oxides in
        oxidant formation particularly at oxidant levels near the standard.
    •   Determine the contribution of natural sources and sinks of hydrocarbons,
        nitrogen oxides and oxidants on oxidant ]evels in the lower atmosphere in
        both rural and  urban areas.
    •   Develop  more reliable methods for relating emissions of precursors  and
        the concentrations  of oxidants observed  in the  atmosphere.
    •   Expand the aerometric data base for  oxidants and precursors through-
        out the United States .
    •   Develop detailed  emission inventory data by place, time of day, and year
        for both anthropogenic and natural sources of oxidant precursors.

                                      32

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    •   Develop  control technology for stationary  sources at  reasonable cost.

    Much of the needed information from these studies will become available over
the next few years.   In some  other  areas several more years of effort may be
required.  However,  as soon as the information in any area is sufficient to support
an addition or change in strategy, the improvement  can be made.   Thus, it  is
expected by this  process that  the current strategy will evolve into  an optimum
strategy over the next several years.
                                       33

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                                REFERENCES
1.   "Air Quality  Criteria for  Photochemical Oxidants,"  U .S .Department of Health
    Education and Welfare, Publication No. AP-63, March, 1970.

2.   "Health Effects of Air Pollutants,"  Volume  2  of Air Quality  and Automobile
    Emissions Control  , National Academy  of Sciences  and National Academy of
    Engineering, Prepared for the U.S. Senate Committee on Public Works, Serial
    No. 93-24, September, 1974.

3.   Altshuller, A.P.  andBufalini, J.J., "Photochemical Aspects of Air Pollution:
    A Review," Environ. Sci.  Technol. 5, 39, (1971).

4.   Demerjian,  K.L.,  Kerr, J.A.   and  Calvert, J.G.,  "The Mechanism of
    Photochemical Smog Formation," pps.  1-262, in Advances in Environmental
    Science and Technology, Vol. 4, John Wiley and Sons, 1974.

5.   Hecht,  T.A., Seinfeld,   J.H., and Dodge, M.C.,   "Further  Development of
    Generalized  Kinetic  Mechanism  for  Photochemical Smog,"  Environ.  Sci.
    Technol. 8, 327-339, (1974).

6.   University of California,  Riverside,  California Air Environment  4, No. 3,
    1974.

7.   Glasson,  W.A.   and  Tuesday,  C.S.,  "Hydrocarbon Reactivities in  the
    Atmospheric  Photooxidation of Nitric Oxide," Environ.  Sci. Technol. 4, 916-
    924, (1970).

8.   Dimitriades,   B.,   "Effects   of  Hydrocarbon   and  Nitrogen  Oxides   on
    Photochemical Smog Formation," Environ. Sci. Technol. 6, 253-260, (1972).

9.   Code of Federal Regulations 40, Parts 50-87, July 1,  1974.

10. Schuck, E.A., et.  al. , "Relationship of Hydrocarbons  to Oxidants in Ambient
    Atmospheres," Jr.  APCA  20, 297-302, May, 1970.

11. County of Los Angeles, Air Pollution Control District,  Rules and Regulations,
    Rule 66, 66.1, 66.2.

12. Horowitz, J.  and Kuhrtz, S., "Transportation  Controls to  Reduce Automobile
    Use and Improve  Air Quality  in Cities,"  U.S.  Environmental  Protection
    Agency, EPA-400/11-74-002, November 1974.

13. "The National Air Monitoring Program  Air Quality and Emissions  Trends,
    Annual Report," Volume 1.,  U.S. Environmental Protection Agency, EPA-
    450/1-73-001-a, p. 1-13,  August 1973.

14. "Monitoring  and  Air Quality Trends  Report,  1972,"  U.S.  Environmental
    Protection Agency, EPA-450/1-73-004, pp. 4-14-28, December, 1973.


                                       34

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15. "Monitoring  and  Air Quality Trends  Report,  1973,  "U.S.  Environmental
    Protection Agency, EPA-450/1-74-007, pp. 77-79, October, 1974.

16. Altshuller, A.P., "Evaluation of Oxidant Results at CAMP Sites in the United
    States," Jr. APCA 25, pp.  19~24, January, 1975.

17. State of California Air Resources Board,  "Ten Year Summary of California Air
    Quality Data,  1963-1972," January,   1974  and  California Air Quality  Data
    Quarterly Reports, 1973-1974.

18. Decker,  C.D., et. al. ,  "Investigation of Rural Oxidant Levels as Related  to
    Urban   Hydrocarbon  Control  Strategies,"   Research   Triangle  Institute,
    Prepared for  U.S.  Environmental  Protection  Agency,  EPA-450/3-75-036,
    March, 1975.
19. Cleveland, W.S. ,  et.al. ,  "Sunday and Workday Variation in Photochemical Air
    Pollutants in N.J.  and N.Y.,"  Science  186. 1037-1038 (1974) and Science 186,
    257(1974).

20. Johnston, D.R. , "Investigation of High Ozone Concentrations in the Vicinity of
    Garrett County,  Maryland and  Preston County, West  Virginia,"  Research
    Triangle Institute, Prepared for U.S. Environmental Protection Agency, EPA-
    R4-73-019, January, 1973.

21. Johnston,  D.R.,  et.  al. ,  "Investigation  of  Ozone  and  Ozone  Precursor
    Concentrations at  Non-urban Locations  in the  Eastern  U.S.,"  Research
    Triangle Institute, Prepared for U.S. Environmental Protection Agency, EPA-
    450/3-74-034, May, 1974.

22. "Monitoring  and  Air  Quality Trends  Report,  1973,"  U.S.  Environmental
    Protection Agency, EPA-450/1-74-007, pp. 117-125, October, 1974.

23. Dutsch,  H.U.,  "Photochemistry  of Atmospheric  Ozone,"  in  Advances  in
    Geophysics, Vol.  15, pps. 219-322, Academic Press, 1971.

24. Shlanta, A.,  and  Moore,  C.D.,  "Ozone and Point  Discharge Measurements
    under Thunderclouds," Jr. Geo. Res. 77, pps 4500-4510, August 20, 1972.

25. Rasmussen,  R.A.,  and  Robinson,  E.,  "The Role  of  Trace  Atmospheric
    Constituents   in  a  Surface  Ozone  Model,"  Washington  State  University,
    Pullman, Washington, 1975.

26. Rasmussen, R.A., et. al., "Measurement of Light Hydrocarbons in the Field
    and Studies  of Transport of  Oxidant Behind an  Urban Area," Final report,
    Contract No.  68-02-1232, Washington State. University (In preparation).

27. Cleveland, W.S.,  and Kleinger, B.,  "The  Transport of Photochemical Air
    Pollution from the Camden-Philadelphia Urban  Complex,"  Bell Laboratories,
    presented at AAAS Annual Meeting, New York, 1975.

28. Blumenthal, D.L., et.  al. ,  "Determination of the Feasibility of the Long-Range
    Transport  of Ozone  or  Ozone Precursors,"  Meteorology  Research,   Inc.,
    Prepared  for  U.S.  Environmental  Protection  Agency,  EPA-450/3-74-061,
    November, 1974.

                                      35

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                                   TECHNICAL REPORT DATA
                            (Please read Instructions on the reverse before completing)
 1 REPORT NO.
   EPA-450/2-75-005
                                                           3 RECIPIENT'S ACCESSION-NO.
 4. TITLE AND SUBTITLE
  Control of Photochemical  Oxidants - Technical  Basis
  and Implications  of Recent Findings
             5. REPORT DATE
             July 15,  1975  (date of issue)
             6. PERFORMING ORGANIZATION CODE
 7 AUTHOR(S)
                                                           8. PERFORMING ORGANIZATION REPORT NO
9 PERFORMING ORGANIZATION NAME AND ADDRESS
  U.S. Environmental  Protection Agency
  Office of Air and  Waste Management
  Office of Air Quality  Planning and Standards
  Research Triangle  Park, North Carolina  27711
                                                           10. PROGRAM ELEMENT NO.
             11. CONTRACT/GRANT NO.
 12. SPONSORING AGENCY NAME AND ADDRESS
                                                           13. TYPE OF REPORT AND PERIOD COVERED
                                                             policy paper
                                                           14. SPONSORING AGENCY CODE
 15. SUPPLEMENTARY NOTES
 16. ABSTRACT
       The report  assesses laboratory and field  studies conducted over  the  past
  several years and  discusses how the findings affect current and projected
  programs to control  oxidants.  Both maximum concentrations and the  frequency
  of violations of the air quality standards for oxidants have decreased  in some
  urban areas as a result of recently initiated  controls.  However, long  thought
  to be primarily  an urban problem, oxidant  levels  well in excess of  the  standard
  have been observed in broad areas in the eastern  third of the U.S.  Although
  naturally occuring sources such as vegetation  and the stratosphere  do contribute
  to these high levels, man's activity is their  predominant cause.  Instances
  are noted in which oxidants and their precursor compounds have been carried  up to
  50 miles, and probably farther.  More extensive control of oxidant-producing
  compounds will be  required in rural areas while emphasis continues  to be
  placed on control  in the cities.
                                KEY WORDS AND DOCUMENT ANALYSIS
                  DESCRIPTORS
                                              b.lDENTIFIERS/OPEN ENDED TERMS
                                                                         c.  COS AT I Field/Group
  photochemical oxidants
 8. DISTRIBUTION STATEMENT

  release unlimited
19. SECURITY CLASS (This Report)
   Unclassified
21 NO OF PAGES

     42
                                              20 SECURITY CLASS (This page)
                                                  Unclassified
                                                                         22. PRICE
EPA Form 2220-1 (9-73)
                                            37

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