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-
nSy Printed on Recycled Paper
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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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