EPA-600/4-78-014
                                          February 1978
   A PROLONGED, LARGE SCALE, OFF-SEASON
      PHOTOCHEMICAL OXIDANT EPISODE
           Gerard A.  DeMarrais
   Meteorology and Assessment Division
Environmental  Sciences Research Laboratory
   Research Triangle  Park, N.C.  27711
ENVIRONMENTAL SCIENCES RESEARCH LABORATORY
    OFFICE OF RESEARCH AND DEVELOPMENT
   U.S. ENVIRONMENTAL PROTECTION AGENCY
   RESEARCH TRIANGLE PARK, N.C.  27711

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                                  DISCLAIMER
     This report has been reviewed by the Office of Research  and Development,
U.S. Environmental  Protection Agency, and approved for publication.   Mention
of trade names or commercial  products does not constitute endorsement or
recommendation for use.
     Mr. DeMarrais is a meteorologist in the Meteorology and Assessment
Division, Environmental Sciences Research Laboratory, Environmental  Research
Center, Research Triangle Park, N.C. 27711.  He is on assignment from the
National Oceanic and Atmospheric Administration, U.S. Department of Commerce.

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                                  ABSTRACT
                                              o
     Oxidant concentrations exceeding 160 yg/m  were observed at  many locations
in a 7-county area in southern California from February  25  to March 4,
1975.  Because this was a violation of the air quality standard at a  time
when relatively low concentrations were normally anticipated the  meteorological
conditions associated with this large scale episode were evaluated.   A more
complete understanding of the meteorology associated with the episode should
provide a better background for devising an abatement strategy.   The  episode
was associated with very slow air movement, slightly elevated temperatures,
abundant solar radiation, limited vertical mixing at the coast, and vertical
mixing varying from negligible at night to relatively deep  in the daytime  at
inland sites.  The maximum temperatures were 3° to 6°C cooler than those
normally associated with high oxidant concentrations, but the solar radiation,
as deduced from sky cover and sunshine records, was about equivalent  to that
at the end of the usual oxidant season.  The differences in vertical  mixing,
combined with the overall stagnation and weak sea breeze at the surface in the
afternoon, appeared to cause the oxidant concentrations  to  be higher  inland.
                                    111

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                                  CONTENTS
Disclaimer	ii
Abstract	111
Figures	    v1
Tables	v11
     1.  Introduction	    1
     2.  Conclusions	    2
     3.  Background and Methods 	    3
              Ozone and total oxldant monitoring stations and the data    3
              Meteorology previously associated with high POX
              concentration  	    3
              Meteorological data	    4
     4.  Results	    6
              POX concentrations	    6
              Surface weather observations	     7
              Daily weather maps	    9
              Special  solar radiation data	    9
              Temporal and spatial variation of bases and tops of
              inversions	    10
     5.  Summary	    12
References	14-16

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                                   FIGURES

Number                                                                   Page

  1.  POX monitoring stations	21

  2.  Maximum hourly POX concentrations  (pphm),  February  25, 1975.  ...  22

  3.  Maximum hourly POX concentration  (pphm),  February 26, 1975  ....  23

  4.  Maximum hourly POX concentration  (pphm),  February 27, 1975  ....  24

  5.  Maximum hourly POX concentration  (pphm),  February 28, 1975  ....  25

  6.  Maximum hourly POX concentration  (pphm),  March  1, 1975  	  26

  7.  Maximum hourly POX concentration  (pphm) March 2, 1975	27

  8.  Maximum hourly POX concentration  (pphm) March 3, 1975	28

  9.  Maximum hourly POX concentration  (pphm) March 4, 1975	29

 10.  Diurnal, clear sky values of k.   The  photodissociation rate constant
      for N02 for Los Angeles  (34.1°N,  118.3°W)	30

 11.  Variation of height and  temperature  (°C)  of bases  (0) and tops  (a)
      of inversions	31
                                      vi

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                                   TABLES



Number                                                                   Page



  1   Meteorology During Episode of February 25  to  March  4,  1975.  .  .    17-19



  2  Values of k  for March 1  Divided by k   for June  21	      20

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                                   SECTION 1
                                  INTRODUCTION
       The concentration of photochemical  oxidant (POX)  is  considered a problem
when it exceeds the hourly National  Ambient Air Quality  Standard (NAAQS) of
        3          1
160 yg/tn  or 8 pphm .  In California POX is measured as  total  oxidant* and ozone,
and the typical months of high POX concentrations are usually  considered to be
                   1 A
May through October   .  The reasons suggested  for the nonoccurrence of high
concentrations in the cool half of the year are that the temperatures are not
high enough and the solar radiation is insufficient for  substantial  oxidant
                                        o
formation.  However, a quarterly summary  of the California Air Resources Board
shows that during the period of February 25 through March 4, 1975,  a large
number of stations in 7 counties in southern California  recorded concentrations
which violated the standard.  Since a more complete knowledge  of the meteorology
associated with these high concentrations could aid in the  formation of an
improved abatement strategy, this investigation was undertaken to obtain that
knowledge.  The meteorological conditions associated with the  episode are
examined and summarized to suggest which phenomena appeared to contribute to
the high concentrations.  The temperature and radiation  observations of the
period are compared to those of the POX season.  In addition,  special con-
sideration is given to the temporal  and spatial variation of the bases and tops
of inversions as shown by the vertical soundings made at Los Angeles Airport
and El Monte5.
*Specific spectroscopic measurements indicate ozone is the principal  oxidant
 in California air?.
                                      1

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                                 SECTION  2
                                CONCLUSIONS
     On the basis of the analyses of the  February  25  to March 4, 1975 southern
California data, the following conclusions are  drawn:
     1.  This  prolonged period of high  POX concentrations occurred at a time
         when  high concentrations were  not a  normal occurrence.
     2.  The episode was associated with  stagnation,  slightly elevated tempera-
         tures, abundant sunshine, limited vertical mixing at the coast,  and
         vertical mixing varying from negligible at night to relatively deep
         in the daytime at inland sites.
     3.  The maximum temperatures were  about  3° to 6°C cooler than those
         normally assciated with high POX concentrations, but the radiation,
         as deduced from the NOp photodissociation rate constant, k,, was
         about equivalent to that at the  end  of the usual POX season  (about
                                                               _3
         11 hours duration and a maximum  rate constant of 8 x 10   per
         second).
     4.  The differences in vertical mixing combined  with the overall stagna-
         tion  and weak sea breeze at the  surface in the afternoon appeared
         to cause the POX concentrations  to be  higher inland.

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                                 SECTION 3
                           BACKGROUND AND METHODS
OZONE AND TOTAL OXIDANT MONITORING STATIONS AND THE DATA
     The southern California area has a large  network  of ozone  and  total  oxi-
dant monitoring stations.  Although the total  oxidant  monitors  react  to
nitrogen dioxide and organic peroxides, ozone  is the principal  oxidant
                 o
in California air .   All of the total oxidant  monitors in southern  California
are colorimetric instruments and are standardized against ozone.  The ozone
concentrations are determined by instruments utilizing one of two physiochemical
processes:  non-dispersive ultraviolet absorption or chemiluminescence.   Both
                                                                        2
types of instruments are calibrated using known constant ozone  standards  .
     A special note  is needed here because of  a change in the recording  of
POX values in California.  There was a discrepancy in  the POX values  recorded
by the Los Angeles Air Pollution Control  District and  the other control
agencies.  All POX data collected beginning June 1, 1975 are  comparable  and
to make all  prior data comparable, the reported non-Los Angeles County data
are to be multiplied by 0.8 .  Accordingly, all  non-Los Angeles County data
in this report have  been made comparable.
     The locations of the ozone and total oxidant stations  are  shown  in
Figure 1.  Many stations record both ozone and total oxidant, and several
cities have more than one station.  The interest in this study  is the highest
concentration of POX for each day without regard to whether it  was  observed
as ozone or total oxidant.  In the presentations that  follow, only  the highest
hourly concentration is shown, and ozone and oxidant are used interchangeably
with each other and  with POX.
METEOROLOGY PREVIOUSLY ASSOCIATED WITH HIGH POX CONCENTRATION
     The meteorological conditions associated  with high POX concentrations
in southern California have been documented in many investigations     .   The
earliest study  correlated high concentrations of POX  with  weak winds and

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                                                       8-11
 stagnant  air.   Other early  comprehensive investigations "   related variations
 in  ozone  concentrations to  variations in the following:  intensity and dura-
 tion  of solar  radiation;  surface temperature; the depth of the polluted layer
 (the  top  coincided with the  base of the subsidence inversion); and wind
 speed and direction.   In  these early studies high concentrations were con-
                                                                 12
 sidered local,  low-level  problems.  However, following the report   that
 winds aloft  are important in  transporting  "second-hand" ozone to unsuspecting
 downwind  areas, investigators examined the three-dimensional picture and
                                         I O 1C
 long-range transport phenomena.  Evidence  '   confirms that high POX con-
 centrations  are frequently  in the air aloft, even within the subsidence
 inversion, and  that the locations of these contaminated layers aloft are
 determined by  the winds aloft.   Eventually, parts of the contaminated layers
                                                            17 18
 are brought  to  the surface  in daytime mixing.  Other studies  '   have shown
 that  the  highest ozone concentrations occur with heat waves.  Finally, although
                   19  20
 some  investigations   '    have indicated that stratospheric ozone may contribute
 to  high surface ozone  concentrations in other places, no similar finding has
 been  reported  for southern  California.
jMETEOROLOGICAL  DATA
                                     21 22
      The  surface weather  observations   '   in this report are from the follow-
 ing stations:   Burbank Airport,  Los Angeles International Airport, Los Angeles
 Civic Center,  Ontario  Airport, Riverside Airport, Norton Air Force Base (San
 Bernardino), and San Diego  International Airport.  The meteorological parameters
 summarized are: the daily  maximum and minimum temperatures, the prevailing
 wind direction and average  speed for each  quarter-day, the percent of possible
 sunshine  for each day, sky  condition for each day and weather (obstructions to
 visibility,  precipitation)  that  occurred during the day.
      Discussions of  the synoptic conditions are based on the Daily Weather
    ??                      5
 Map   and the  daily  resumes  of  the  National Weather Service Air  Pollution
 Forecaster in  Los Angeles.   The  Daily Weather Map is used to locate high and
 low pressure areas and fronts.   The  Daily  Weather Map shows two maps for each
 day based on 4 a.m.  (all  times are  Pacific Standard) observations; one map is
 TV   the  surface and  the other for  500 millibars  (mb) (about 5500 meters (m)
 eoove the surface).
      Special attention is given  to  solar  radiation data with emphasis on the
                                       4

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photodi^sociation rate constant, k,, for nitrogen dioxide,  NCL.   This  con-
                                        24
stant is explained in detail by Leighton  .   Ozone production  in  the presence
of ozone precursors is directly related to the value of k,.
     A second phenomenon given special  consideration is the  time  and spatial
variation of the bases and tops of inversions.  Records  from  the National
Weather Service show that a variation does exist which may  partially account
for higher concentrations in the eastern part of the Los Angeles  basin.

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                                 SECTION 4
                                  RESULTS
POX CONCENTRATIONS
     The highest hourly POX value for each day for each station is  shown in
Figures 2 through 9.
     On February 25 (Figure 2) there were violations  of the standard  (8 pphm)
in all  7 counties.  Most coastal  areas had concentrations  at or just  below
the standard, whereas at the inland locations concentrations generally were
higher than the standard by 25 to 75 percent.
     On February 26 (Figure 3) the only coastal  city  with  a violation was Chula
Vista in San Diego County and 4 inland cities—Newhall, Temple City,  Upland,
and Fontana--had concentrations which were twice as high as the standard.
     On February 27 (Figure 4) the coastal stations just below Los  Angeles had
low concentrations whereas El Toro and the coastal stations in San  Diego had
violations.  Inland, 7 stations recorded concentrations twice the standard and
                         o
several exceeded 400 vig/m  (20 pphm).
     On February 28 (Figure 5) the only areas without violations were on the
immediate coast and areas within 16 km of the coast had readings ranging from
               o
200 to 420 yg/m  (10 to 21 pphm).  Inland the average concentrations  were
about twice the standard and a violation was noted at Victorville in  the
desert to the north as well as at Palm Springs in the eastern desert.
     On March 1 (Figure 6) violations occurred throughout  the 7-county area
with the coast being relatively clean and inland areas badly contaminated.
     On March 2 (Figure 7) violations were reported in only 4 counties, the
coast was relatively clean, and inland the concentrations  were lower  than
they were on March 1.
     On March 3 (Figure 8) the concentration pattern  was similar to that of
March 2, but fewer stations recorded violations, 20 versus 17.
                                     6

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     On March 4 (Figure 9) only 2 violations  occurred  in  northwest  Los Angeles
County and 1  occurred in eastern Orange County.   Large parts  of western  San
Bernardino and Riverside counties had violations.
SURFACE WEATHER OBSERVATIONS
     The maximum temperatures at the 7 stations  (Table 1) reveal  that the
period averaged slightly warmer than the long term average at the coast, while
inland it was 3° to 6°C warmer than average.   However, these  temperatures  were
about 6° to 8°C colder than those of July.  These maximum temperatures show  the
normal condition of marked increase from the  coast inland. Los Angeles  Airport
had temperatures around 15°C while Ontario  and San Bernardino had temperatures
in the range of 26° to 32°C (80's°F).  These  higher temperatures inland  indicate
that such locations had vertical mixing to  considerably greater heights  than
the coastal locations.
     The diurnal range of temperature (today's maximum minus  tomorrow's  mini-
mum) shows where radiation Inversions likely  form at night; when the  range
is 14°C or greater at a location in southern  California there is a  very  high
                                                        25
probability that nocturnal surface-based inversions form  .  These  maximum-
minimum temperature ranges in Table 1 indicate that inland locations  must
have had nocturnal inversions almost every  night while coastal  areas  did not
have these surface-based inversions.  The Los Angeles  and El  Monte  data,
which are limited to the workweek days and  are presented in a following  sec-
tion, showed that the coast generally did not have surface-based inversions
while El Monte did have them.  The periods  of warming  and cooling,  particularly
at inland locations, were neither associated  with increases and decreases  in
concentrations nor expansion and contraction  of the affected  areas.
     The winds were generally light except  during the  third quarter of each
day.  During this afternoon period, there was a  sea breeze flow with  a general
west-to-east movement, except at Burbank where a sea breeze comes out of the
south-southeast.
     The two sunshine records reveal that the coastal  area had two-thirds  or
more of the possible sunshine on each of the  first 7 days; on the eighth day
the sunshine was markedly less.

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     The sky conditions (as well  as the temperatures)  at  the  inland  stations
indicate that they had greater amounts of sunshine than  the coastal  sites.
Smoke and haze were consistently present after the first  day.   At  the  4  suc-
cessive downwind stations, Burbank, Ontario, San Bernardino,  and Riverside,
the smoke and haze were dense enough to partially obscure the  sky; the visi-
bility generally was less than 5 km at these stations.
     The overall indication was that the episode was not  associated  with
particularly high temperatures; there was slow moving  air;  the  sunshine was
abundant; inland, there was limited nocturnal  vertical mixing  and  relatively
deep daytime mixing; and obscuring phenomena tended to stay in  the area.
     The higher concentrations at inland than  at coastal  locations are assumed
to have been due, partially, to differences  in vertical mixing.  The typical
diurnal air movement shows ozone and its precursors being carried  inland with
              14
the sea breeze   in the daytime while a weaker reverse flow exists at  night.
The wind directions at Los Angeles, Ontario, and Burbank  indicate  that this
diurnal flow occurred during this period (Table 1). In the daytime, the more
polluted air (Figures 2-9) that was inland was dispersed  by vertical mixing
through deeper layers than the polluted air  in coastal areas.   Then, at  night,
there was a reverse flow and in the eastern  areas radiation inversions formed
(Figure 11), cutting off mixing between the  surface and layers  aloft.  Since
                                                pc
the ground is a sink at which ozone is destroyed  , a  contrast  was set up
between inland areas and the coast.  Inland  the ozone  aloft remained intact,
except for scavenging by the NO present in that layer.  At the  coast,  vertical
mixing continued through the night and the relatively  shallow  ozone  reservoir
aloft was diluted by mixing with the surface air; part of the  ozone  was
destroyed at the surface so the concentrations aloft and  at the surface  de-
creased with time.  The cleansing was augmented by having relatively clean
air advected in with the drainage winds from inland areas; these drainage
winds had little or no contact with the ozone aloft and  the operations of
the sources of precursors (primarily autos)  inland were  greatly reduced.   In
the following daylight periods during the first few hours, the emissions of
precursors increased tremendously throughout the Basin and the sea breeze winds
mo,^ the air eastward.  The abundant sunlight (Table  1)  reacted with  the
precursors to produce ozone.  The coastal areas had few  upwind sources and
                                       8

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they had relatively low concentrations while areas  inland had high concen-
trations.  As the day progressed both the coastal and inland areas had their
surface air mixed with the air aloft.  The coastal  areas  had a relatively
small amount of ozone with which to mix while inland areas had a  deep  layer
with high concentrations of ozone.  This gradient aloft,  from inland to the
coast, although not documented on this occasion, has been documented on other
                                                          13
occasions when similar meteorological conditions prevailed  .  Thus the
inland areas had high concentrations due to the combined  effects  of advection
and the mixing downward of ozone from aloft.  In periods  of slow  air movement,
this source of "second-hand" ozone, coming from aloft, adds  to the ozone
problem associated with surface advection.
DAILY WEATHER MAPS
     The 500-mb maps for February 25 through March  3 generally showed  a weak,
flat ridge over or a little to the east of California. This condition ended
on March 4 when an upper level low with cool, moist air moved Into California.
The surface maps showed pressure gradients which allowed  a very weak onshore
flow from February 25 to March 3.  Weak cold fronts or troughs moved through
the area early on February 27 and March 2.  On March 4 there was  a moderate
onshore gradient; rain fell on some areas of southern California.
SPECIAL SOLAR RADIATION DATA
     Since an episode developed during February 25  through March  4, it 1s
concluded that the solar radiation was sufficient for generation  of signifi-
cant ozone concentrations.  According to the weather observations, the indica-
tion is the radiation was intense for this time of  year.   No direct measure-
ments of solar radiation were made so an alternate  method of evaluating the
radiational effects had to be employed.  Because the N09  photodissociation rate
                                                24
constant, k,, is a key factor in ozone generation   , data on the  temporal
                                          27
variation of k, were sought.  A new method   for calculating the  diurnal
variation cf k, for clear sky conditions (the prevailing  situation) was used
for June 21 and December 21, the seasonal extremes, as well  as for the midday
of the episode, March 1.  The results are shown in  Figure 10.  The values of
k, on March 1 are considerably smaller than those of June 21, but markedly
greater than those of December 21.  On June 21 photodissociation  starts around

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5 a.m. and ends about 6:45 p.m.  whereas  on  March  1  the  starting time  is about
6:45 p.m. and ending time 5:30 p.m.;  the photodissociation occurs  for 3
hours longer on June 21.   Table  2  shows  the ratio of the on-the hour  values
of k.| for March 1  versus  those for June  21.  Only during the middle of the
day are the March  1  values 80 percent of those of June  21.  The overall
indication is that the photodissociation can be considerably reduced  from
the extreme value  and duration,  yet still be sufficient to generate high
ozone concentrations.  In absolute values and durations, a maximum k,  of
      3    1
8 x 10  sec  and a duration just short of 11  hours  seems sufficient when
other conditions are right.  Although the days in this  episode are cold-
season days, the radiation results are not  surprising.  March 1 is comparable
to October 10 with regard to elevation angle of the sun and radiation, and
October 10 is considered  to be near the  end of the  season with high ozone
              2 3
concentrations ' .  (Note:  The  maximum  temperatures, when compared to October
10 averages, were  about 6°C colder on the coast and 3°C colder inland.)
TEMPORAL AND SPATIAL VARIATION OF  BASES  AND TOPS  OF INVERSIONS
     The heights and temperatures  of  the bases and  tops of inversions indi-
cate the potential for vertical  mixing.   When the bases are low and the
temperature differences between  the bases and tops  are  large, there generally
is limited vertical  mixing.  When  the bases are high or the temperature dif-
ferences are small (that  is, the inversion  is easily eliminated with  additional
heating), vertical mixing can be extensive.  In the Los Angeles area  data on
the heights and temperatures of the bases and tops  of inversions are  provided
twice a day, 6 a.m.  and noon, Monday  through Friday, for 2 sites,  Los Angeles
Airport (near Lennox) and El Monte (close to Temple City), by the  National
               23
Weather Service  .  A graphical  presentation of these data for February 25
through March 4 is shown  in Figure 11.  The Los Angeles Airport, a coastal
location, usually  observed inversions with  elevated bases and temperature
differences exceeding 3.0°C (considered  large and not easy to eliminate when
observed at noon ).  The  elevated  bases  were 460  m  or lower most of the time
and the inversions remained intact and intense through  the daytime; relatively
rapid vertical mixing occurred continually  throughout the 24-hour  day, but was
 ; united.  At El Monte, an inland station, most of the 6 a.m. inversions were
surfaced-based, indicating that vertical mixing was very slow and  limited at
                                      10

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night.  At noon over El  Monte the  Inversions were weak  (averaging 1.0°C).and
probably eliminated in the afternoon;  vertical mixing had  no  inversion lid.
Normally, this better daytime vertical  mixing  inland would mean  greater dilution
by mixing with a larger volume of  clean air aloft.  However,  the winds aloft up
to about 900 m from February 25 through March  3 were light and variable  , indi-
                                                       11  12  13
eating very slow movement aloft.  It is well-documented  '  '    that ozone
buildup occurs during periods with sluggish air movement aloft and that the
layers aloft can be the source of  "second-hand" ozone brought down to the surface
by vertical mixing.  The "second-hand"  ozone might  have been  a major contributing
factor to the extremely high concentrations observed at stations in the vicinity
of El Monte.
                                      11

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                                  SECTION 5
                                   SUMMARY
1.  During the cool part of the year when high POX concentrations  do  not  nor-
mally occur, there was an 8-day period when a 7-county area in  southern Cali-
fornia experienced a POX episode.
2.  The episode was associated with stagnation; the winds  at the surface  and
aloft were light.  At the surface, there was a very weak land breeze  at night
and during the day an organized onshore flow.
3.  The episode was associated with relatively warm temperatures and  intense
radiation for the season, (as deduced from sky cover and sunshine  records).
The maximum temperatures were considerably lower than those which  occur during
the peak POX season and even 3° to 6°C lower than those which occur at the end
of the POX season in the fall.  The radiation, as shown by the  photodissocia-
tion rate, k,, for N02» was considerably less than that observed at the height
of the POX season, but similar to that at the end of the normal  POX season.
4.  There was a marked difference in the vertical mixing at the coast and
inland.  Vertical mixing was continuous, but limited throughout the 24-hour
day at the coast, while inland there was negligible mixing at night and
relatively deep mixing in the daytime.
5.  The differences in vertical mixing may have accounted, in part, for the
differences in the severity of the problem.  The higher concentrations occurred
inland where vertical mixing during the daytime brought down oxidant  from the
previous day that had been trapped aloft.  Each day more POX was added near
the surface, and there was no clean air aloft with which to dilute the surface
concentrations.  At the coast vertical mixing allowed for a relatively uniform
vertical distribution of POX, which enhanced destruction at night  near the
surface.  Additionally, the coastal area benefited from the organized afternoon
flu ~> at the surface that brought relatively clean air to the coast.
                                      12

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Simultaneously, the inland areas  were  having  high concentrations of ozone
advected in from the coast and brought down from aloft; the ozone problem
inland was compounded.
                                      13

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                                 REFERENCE

 1.   National  Air Pollution  Control Administration.  Air Quality Criteria for
     Photochemical  Oxidants.  AP-63, U.S. Department of Health Education, and
     Welfare,  Washington,  D.C.  1975.  178 pp.

 2.   California  Air Resources Board.  California Air Quality Data, January,
     February, March 1975.   Technical Services Division, Sacramento, California,
     1975.   75 pp.

 3.   Schuck,  E.A.,  A.P. Altshuller, D.S. Barth, and G.B. Morgan.  Relationships
     of  Hydrocarbons to Oxidants  in Ambient Atmospheres.  J. Air Poll. Control
     Assoc.,  20:   297-302  (1970).

 4.   Dimitriades, B.  Photochemical Oxidants in the Ambient Air of the United
     States.   EPA-600/3-76-017, U.S. Environmental Protection Agency, Research
     Triangle  Park, North  Carolina, 1976.  182 pp.

 5.   Lust,  E.  (Air Pollution Forecaster, National Weather Service, Los Angeles),
     Daily  worksheets  for  air pollution forecasts and radiosonde data for Los
     Angeles  and El Monte, February 24 through March 5, 1975.

 6.   California  Air Resources Board.  California Air Quality Data, July, August,
     September 1975.  Technical Service Division, Sacramento, California.
     75  pp.

 7.   Middleton,  J.T.,  J.B. Kendrick, and H.W. Schwalm.  Injury to Herbaceous
     Plants by Smog or Air Pollution.  Plant Disease Reporter, 34(9):  245-252,
     1950.

 8.   Neiburger,  M.  and J.  Edinger.  Meteorology of the Los Angeles Basin,
     Report No.  1,  Southern  California Air Pollution Foundation, Los Angeles,
     California, 1954. 97 pp.

 9.   Renzetti, N.A., Editor.  An  Aerometric Survey of the Los Angeles Basin
     August-November 1954.   Report No. 9, Air Pollution Foundation, Los Angeles,
     California, 1955.

10.   Hitchcock,  L.B.,  W.L. Faith, M. Nieburger, N.A. Renzetti, and L.H. Rogers.
     Air Pollution Situation in Los Angeles-An Aerometric Survey.  In:  Pro-
     ceedings of the Third National Air Pollution Symposium, Pasadena, Cali-
     fornia, 1955.   pp.  12-23.

11.   Rogers, L.H.  Report  on Photochemical Smog.  J. of Chem. Education, 35(6):
     310-313, 1958.


                                     14

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12.  Lea, D.  A.   Vertical  Ozone Distribution  in  the  Lower Troposphere Near an
     Urban Pollution Complex.   J.  Appl.  Meteorol., 7:   252-267,  1968.
                        i
13.  Edinger, J.G.   Vertical  Distribution  of  Photochemical  Smog  in  Los Angeles
     Basin.   Environ.  Sci.  Technol.,  3:  247-252, 1973.

14.  Gloria,  H.R.,  G.  Bradburn, R.F.  Reinisch, J.N.  Pitts,  Jr.,  J.V. Behar,
     and L.  Zafonte.  Airborne Survey of Major Air Basins in  California.
     J. Air Poll.  Control  Assoc.,  24(7):  645-652, 1974.

15.  Blumenthal,  D.L., L.A. Farrow, and  T.A.  Weber.  The Effects of Variations
     in Bulk  Meteorological Parameters on  Ozone  Concentrations.  In Preprint
     Volume:   Symposium on Atmospheric Diffusion and Air Pollution, Amer.
     Meteor.  Soc.,  Santa Barbara,  California, 1974.  pp.  115-120.

16.  Kauper,  E.K.  and  B.L.  Niemann.   Los Angeles to  Ventura Over Water Ozone
     Transport Study.   Report prepared for California Air Resources Board by
     Metro Monitoring  Services, Covina,  California,  1975.   54 pp.

17.  California Air Resources Board.   California Air Quality  Data,  April, May,
     June 1974.   Technical  Services Division, Sacramento, California, 1974.
     83 pp.

18,  Tiao, G.C.,  G.E.P. Box,  and W.J. Hamming.   Analysis of Los Angeles
     Photochemical  Smog Data:   A Statistical  Overview.  J.  Air Poll. Control
     Assoc.,  25(3):  260-268, 1975.

19.  Danielson, E.F. and V.A. Mohnen. Ozone  Measurements and Meteorological
     Analyses of  Tropopause Folding.   Presented  at the  International Symposium
     on Ozone, Dresden, German Democratic  Republic,  1976.   36 pp.

20.  Reiter,  E.R.   The Role of Stratospheric  Import  on  Trosposp&eric Ozone
     Concentrations.  Presented at the International Symposium on Ozone,
     Dresden, German Democratic Republic,  1976.  24  pp.

21.  U.S. Department of Commerce,  National  Oceanic and  Atmospheric  Administra-
     tion.  Local  Climatological Data.   Published monthly for Los Angeles and
     San Diego, 1975.   2 pp.

22.  National Climatic Center, Surface Weather Observations,  Burbank, Norton
     AFB, Ontario,  FAA Riverside,  February 25-March  4,  1975.  (Xerox copies of
     original records).

23.  U.S. Department of Commerce,  National  Oceanic and  Atmospheric  Administra-
     tion.  Daily Weather  Maps. Published weekly 1975.  8  pp.

24.  Leighton, P.A.  Photochemistry of Air Pollution Academic Press, New York,
     New York, 1961.  300  pp.
                                     15

-------
25.  DeMarrais, G.A., G.C.  Holzworth,  and C.R.  Hosier.  Meteorological Summaries
     Pertinent to Atmospheric Transport and  Dispersion  Over Southern California.
     Technical Paper. No.  54.  U.S.  Department  of  Commerce, Weather Bureau,
     Washington, D.C., 1965.   86 pp.

26.  Miller, A. and C.D.  Ahrens.  Ozone Within  and Below  the West  Coast Tempera-
     ture Inversion.  Dept. of Meteorology Report  No. 6,  San Jose  State College,
     San Jose, California,  1969.  74 pp.

27.  Schere, K.L. and K.L.  Demerjian.   Calculation of Selected  Photolytic Rate
     Constants Over a Diurnal Range-A Computer  Alogorithm.  EPA-600/4-77-015,
     U.S. Environmental  Protection Agency, Research Triangle Park, North
     Carolina, 1977.  63 pp.
                                      16

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                                  TECHNICAL REPORT DATA
                           (Please read Instructions on the reverse before completing)
1  REPORT NO.
  EPA-600/4-78-014
                             2.
4 TITLE AND SUBTITLE

  A PROLONGED,  LARGE-SCALE,  OFF-SEASON, PHOTOCHEMICAL
  OXIDANT EPISODE
                                       5. REPORT DATE
                                       February  1978
                                      6. PERFORMING ORGANIZATION CODE
                                                          3. RECIPIENT'S ACCESSION-NO.
7. AUTHOR(S)
                                                          8. PERFORMING ORGANIZATION REPORT NO.
  Gerard A. DeMarrais*
9. PERFORMING ORGANIZATION NAME AND ADDRESS
  Environmental  Sciences  Research Laboratory
  Office of Research  and  Development
  U.S. Environmental  Protection Agency
  Research Triangle  Park, NC  27711
                                       10. PROGRAM ELEMENT NO.

                                         1AA603 AD-07(FY-78)
                                       11. CONTRACT/GRANT NO.
12. SPONSORING AGENCY NAME AND ADDRESS
  Environmental  Sciences  Research Laboratory - RTP, NC
  Office of Research  and  Development
  U.S. Environmental  Protection Agency
  Research  Triangle  Park, NC  27711
                                         FYPE OF REPORT AND P-ERIOQCOVERED
                                         Inhouse  War //-Dec 77
                                       14. SPONSORING AGENCY CODE

                                         EPA/600/09
15. SUPPLEMENTARY NOTES
 *0'n assignment  from the National Oceanic and Atmospheric  Administration,
  U.S. Department  of Commerce.
16. ABSTRACT
     Oxidant  concentrations exceeding 160 yg/m  were  observed  at many locations in a
seven-county  area  in southern California from February  25  to March 4, 1975.  Because
this was  a  violation of the air quality standard  at a time when relatively low con-
centrations were  normally anticipated, the meteorological  conditions associated with
this large  scale  episode were evaluated.  A more  complete  understanding of the
meteorology associated with the episode should  provide  a  better background for
devising  an abatement strategy.  The episode was  associated with very slow atr move-
ment,  slightly elevated temperatures, abundant  solar  radiation, limited vertical
mixing at the coast, and vertical mixing varying  from negligible at night to
relatively  deep in the daytime at inland sites.   The  maximum temperatures were
to  6°C cooler than those normally associated with high  oxidant concentrations,
the solar radiation, as deduced from sky cover  and sunshine records, was about
equivalent  to that at the end of the usual oxidant season.  The differences in
vertical  mixing,  combined with the overall stagnation and weak sea breeze at the
surface in  the afternoon, appeared to cause the oxidant concentrations to be higher
inland.
                                                              3°
                                                              but
17.
                               KEY WORDS AND DOCUMENT ANALYSIS
                 DESCRIPTORS
                                             b.IDENTIFIERS/OPEN ENDED TERMS
                                                       COSATl Field/Group
  * Air pollution
  * Ozone
  * Meteorological
  * Evaluation
                           Southern California
data
13B
07B
04B
13.
   iSTRIBUTION STATEMENT
                     RELEASE  TO PUBLIC
                                             19. SECURITY CLASS (This Report)
                                                  UNCLASSIFIED
                                                    21. NO. OF PAGES

                                                      41
                                             20 SECURITY CLASS (This page)

                                                  UNCLASSIFIED
                                                                        22. PRICE
EPA Form 2220-1 (9-73)
                                            32

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