United States
              Environmental Protection
              Agency
Atmospheric Research and Exposure
Assessment Laboratory
Research Triangle Park NC 27711
              Research and Development
EPA/600/S3-91/015 May 1991
EPA      Project Summary
              A Study  Using  a Three
              Dimensional  Photochemical
              Smog  Formation Model  Under
              Conditions of Complex Flow:
              Application of the  Urban Airshed
              Model to the  Tokyo
              Metropolitan  Area
              Shinji Wakamatsu and Kenneth L. Schere
                The purpose of this study  is to
              evaluate the Urban Airshed Model
              (UAM), a three-dimensional photo-
              chemical urban air quality simulation
              model, using field  observations from
              the Tokyo Metropolitan Area. Empha-
              sis was placed on  the photochemical
              smog formation mechanism under
              stagnant meteorological  conditions.
              The UAM produced reasonable calcu-
              lated results for the diurnal, area! and
              vertical distributions of O, concentra-
              tions covering the Tokyo Metropolitan
              Area. The role and  significance of the
              previous day's secondary pollutants on
              O3 formation mechanisms were also in-
              vestigated. During the night time, high
              values of secondary pollutant concen-
              trations were predicted above the ra-
              diation inversion  layer. These  aged
              pollutants were then entrained into the
              mixing layer during the day. in accor-
              dance with the elevation of the lid.
              These characteristic features were also
              observed in the field study.
                This Project Summary was devel-
              oped by EPA's Atmospheric Research
              and Exposure Assessment Laboratory,
              Research Triangle  Park,  NC, to an-
              nounce key findings of the research
              project that  Is fully documented In a
              separate report of the same title (see
              Project Report ordering Information at
              back).
Introduction
  High ozone (O3) concentrations are fre-
quently observed in the Tokyo Metropoli-
tan ^Area (TMA) in the summer season.
The" industrial complexes located  in the
Tokyo Bay area are the largest in Japan
and are the  major stationary sources of
pollutants (NO, NO2, SO2, hydrocarbons, ,
aerosols, etc.), while the Tokyo Metropolis
is the largest contributor of pollutants from
mobile sources. In addition, the topogra-
phy of the area is very complicated, which
leads to complex wind patterns. Reflecting
these circumstances, the relationships
between the precursor emissions and fields
observed O3  patterns are not clearly un-
derstood. Investigating these relationships
requires the  use of a three-dimensional
photochemical air pollution simulation
model. Results from such a model allow
the analysis of the quantitative effects of
the "previous  day's secondary pollutants,
temporal variation of mixing height, and
three-dimensional wind field on O3 forma-
tion mechanisms in the atmosphere.
  The purpose of this study is an evalua-
tion of the  SAI  Urban Airshed  Model
(UAM), a three-dimensional photochemi-
cal urban air quality simulation model, us-
ing observations from a 1981 field experi-
ment in the Tokyo Metropolitan Area, Ja-
pan. From July 15 to July 17 high O3
concentrations were observed in the To-

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kyo Metropolitan Area under conditions of
a complex wind field. During this period
intensive field measurements  of vertical
and horizontal winds and pollutants were
made. These data provide sufficient infor-
mation  to evaluate the  photochemical
smog simulation model for this case-study.

Analysis
  In the first step, input  data were se-
lected from the data base and set up in a
suitable format for the  SAI-UAM and a
test run was then performed. For the sec-
ond  step  the  simulated  results  were
evaluated using  the field observed  data.
Emphasis was placed on the investigation
of diurnal variations and  area! and vertical
distributions of pollutants.  Vertical cross-
sodions of simulated pollutant patterns
are analyzed for the TMA domain, includ-
ing  the diurnal variation in the patterns.
The effects of vertical  meteorological con-
ditions and the previous day's secondary
pollutants are emphasized. Limited O3 field
data from aircraft are compared with the
simulated results.
  In the Tokyo Metropolitan Area higher
concentrations of O3 are usually observed
near the shore in the morning. As the sea
breeze  layer penetrates inland, this high
concentration  region  travels with  it,  in-
creasing in concentration with time. When
the geostrophtc  wind is weak, the sea-
land breeze circulation and the mountain-
valley breeze circulation are the most im-
portant  meteorological factors  in photo-
chemical O3 formation inland.
  A nighttime temperature inversion, which
persists into the early morning, prevents
the dispersion of primary pollutants emit-
ted from the large coastal industrial zones
and  the Tokyo  Metropolitan Area. Two
large industrial  complexes, Keihin and
Keiyo, are located along Tokyo Bay, while
the center of  Tokyo  is  the largest con-
tributor of pollutants from mobile sources.
These pollutants are transported seaward
by the land breeze. Around noon time the
sea breeze brings these pollutants back
inland where they become well mixed un-
der thermal convective conditions. These
primary pollutants are converted into sec-
ondary  pollutants and transported inland
with the sea breeze penetration. Usually,
high O, concentrations are observed aloft
(500-1000 m) in the early morning. This is
an aged O3 layer, and its associated sec-
ondary  pollutants are entrained into the
growing mixing layer in accordance with
the elevation of the lid. This effect is be-
lieved to accelerate the formation of sec-
ondary pollutants during the next day.
   During the period of study, July 15 to
July 20,1981, the weather conditions were
typical of this season  in Japan. A pre-
dominant  northern Pacific high pressure
cell covered the Japanese archipelago and
the pressure gradient was weak. Under
these conditions,  especially  high oxidant
concentrations were observed in  the
southern part of the Tokyo  Metropolitan
Area  due to the  orientation of the sea-
land breeze circulation system to the met-
ropolitan area.
   UAM simulations were conducted over
40  hours  beginning 0400 JST,  July 16,
1981.  Data  from 62  selected ground
monitoring stations, 4 upper-air sounding
sites,  and 23 pilot balloon sites were used
to determine the boundary concentrations
and the meteorological parameter input
values for the model. The aircraft mea-
surements showed a very complex verti-
cal and horizontal  pollutant distribution
mainly  caused  by the  complex wind
structure.  To  simulate  this wind field,  a
three-dimensional mass and momentum-
conserving wind model was  used to pre-
pare the hourly horizontal winds required
by the UAM. The Carbon Bond II chemical
kinetic scheme was used for the chemis-
try calculations in the UAM.  Hourly emis-
sion  rates  were calculated from  area
sources and point sources of NO2 and non-
methane hydrocarbons (NMHC) at each
grid cell. NMHC emissions must be dis-
tributed into  particular  reactivity classes.
To  accomplish this the ratio  of 18 NMHC
species from the  five  major  hydrocarbon
source categories (vehicle exhaust, oil re-
finery facilities, other petrochemical  op-
erations, gasoline vapor, and painting sol-
vents) were determined.
  The area modeled around Tokyo was
183 km wide and  172 km long, with each
individual cell 6.8 km wide  and 5.5 km
long. This individual cell size is based on
the relative degree length of latitude, lon-
gitude of this area. The full horizontal do-
main  is 27 by 30  cells with the outer ring
of cells serving as boundary condition cells.
There are  five layers in the vertical; the
depth of each layer is a function of the
time  of  day. The  bottom three layers
simulated the mixing layer.
Conclusions
  Usually,  in  the  Tokyo  area,  high  O,
concentration areas, which are transported
from inland regions by the nighttime land
breeze, are observed aloft  in the early
morning, and these are entrained into the
mixing layer  in accordance  with  the  el-
evation of the lid. This effect is believed to
accelerate  the formation of secondary
pollutants during the next  day. These ob-
servational results were qualitatively  re-
produced by the Urban Airshed Model. In
this study major efforts were devoted to
clarify the effects of vertical  meteorologi-
cal conditions and the previous day's sec-
ondary pollutants on the second day's O,
concentrations. Simulated  results showed
reasonable performance at reproducing a
three-dimensionaLp.rpfilei.ofLQ3 concentra-
tions. It was found that:
   1. The SAI Urban Airshed Model pro-
duced  reasonable calculated  results  for
the diurnal and area! distributions of  O3
concentrations covering the Tokyo Metro-
politan Area.
  2. Observed vertical  O3 profiles were
also compared with the simulation results.
The simulated vertical  profiles  were in
qualitative  agreement with the observa-
tions although the coarse vertical resolution
and hour averaging  in the model may
have prevented  the prediction  of the
maximum concentrations accurately.
  3. Paraffin (PAR) and aromatic (ARO)
concentrations were underestimated. This
might be caused from an estimation error
in the hydrocarbon emissions.
  The role and significance  of the previ-
ous day's secondary pollutants on O3 for-
mation  mechanisms were  investigated
using the UAM simulations. The largest
differences in the vertical pollutant profiles
between the two days studied were in  the
species O3 and carbonyls  (CARB). During
the second night of simulation, especially
high values of these species were pre-
dicted above the radiation inversion layer.
These aged pollutants were then entrained
into  the mixing layer during the day in
accordance with the elevation of the lid. In
part, because of the higher CARB con-
centration levels on the second day,  O3
levels increased earlier in time and peaked
at higher concentrations than they had on
the first day of simulation.  The importance
of the  effects of the previous day's aged
pollutants are confirmed using the UAM.
                                                                                  . GOVERNMENT PRINTING OFFICE: 1991/548-028/20217

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 The EPA author, Kenneth L. Schere (also the EPA Project Officer, see below),  is on
   assignment to the Atmospheric Research and Exposure Assessment Laboratory,
   Research Triangle Park, NO 27711, from the National Oceanic and Atmospheric
   Administration; Shinji Wakamatsu is with the National Institute of Environmental
   Studies, Tsukuba, Japan.
 The complete report, entitled "A Study Using a Three Dimensional Photochemical
 Smog Formation Model Under Conditions of Complex Flow: Application of the Urban
   Airshed Model to the Tokyo Metropolitan Area," (Order No. PB91-168 401/AS; Cost:
   $17.00, subject to change)  will be available only from:
         National Technical Information Service
         5285 Port Royal Road
         Springfield, VA 22161
         Telephone: 703-487-4650
 The EPA Project Officer can be contacted at:
         Atmospheric Research and Exposure Assessment Laboratory
         U.S. Environmental Protection Agency
         Research Triangle Park, NC 27711
 United States
 Environmental Protection
 Agency
Center for Environmental
Research Information
Cincinnati, OH 45268
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Penalty for Private Use $300
EPA/600/S3-91/015

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