Tropospheric ozone production and transport in mid-latitude eastern Asia is studied. Data analysis of surface-based ozone measurements in Japan and satellite-based tropospheric column measurements of the entire western Pacific Rim are combined with results from three-dimensional model simulations to investigate the diurnal, seasonal and long-term variations of ozone in this region. Surface ozone measurements from Japan show distinct seasonal variation with a spring peak and summer minimum. Satellite studies of the entire tropospheric column of ozone show high concentrations in both the spring and summer seasons. Finally, preliminary model simulation studies show good agreement with observed values

Carmichael, Gregory R.

Young, Sun-Woo

English

NASA Technical Reports Server

N95- 10602
3o216 v
TROPOSPHERIC OZONE IN THE WESTERN PACIFIC RIM : ANALYSIS OF
SATELLITE AND SURFACE-BASED OBSERVATIONS ALONG WITH
COMPREHENSIVE 3-D MODEL SIMULATIONS
Young Sunwoo and Gregory R. Carmichael
Department of Chemical and Biochemical Engineering
Center for Global and Regional Environmental Research
The University of Iowa
Iowa City, Iowa 52242, USA
ABSTRACT
Tropospheric ozone production and transport in mid-
latitude eastern Asia is studied. Data analysis of surface-
based ozone measurements in Japan and satellite-based
tropospheric column measurements of the entire western
Pacific Rim are combined with results from three-
dimensional model simulations to investigate the diurnal,
seasonal and long-term variations of ozone in this region.
Surface ozone measurements from Japan show distinct
seasonal variation with a spring peak and summer minimum.
Satellite studies of the entire tropospheric column of ozone
show high concentrations in both the spring and summer
seasons. Finally, preliminary model simulation studies
show good agreement with observed values.
1. INTRODUCTION
The characteristics of tropospheric ozone production
and transport in the middle latitudes of the western Pacific
Rim region are being studied. This region, which includes
the countries of China, Japan, and Korea, is undergoing
accelerated economic growth and industrial expansion
resulting in, among other things, unprecedented increases in
the anthropogenic emissions of ozone precursors such as
nitrogen oxides and hydrocarbons. It has already been
shown that this region of Asia has the highest tropospheric
ozone column values anywhere on earth (Fishman et al.,
1990). Thus, the effects of tropospheric ozone in this region
are clearly significant and, furthermore, its impact on the
global troposphere remains unquantified. In this paper
results from both satellite and surface data analyses and
those from preliminary three-dimensional simulations on a
regional scale using a detailed tropospheric trace gas model
(i.e., the STEM-II model) are presented.
2. SURFACE DATA ANALYSIS
The surface-based observations of ozone are from
the Background Surface Ozone Monitoring Network of
Japan which was establishcd in the 1980's (NIES Reports,
1989). There are over ten monitoring stations dispersed
throughout Japan mostly at sites such as mountain tops and
remote islands. The time span of data collection varies with
station ranging from six years to three months of hourly
values. Over the entire sampling peritx.t, about half of the
stations, most of them from thc island of Honshu, show an
increase of 1-5% in the monthly average of hourly
measurements while the rest of the stations show no visible
trend in either direction. Figure 1 shows the monthly
maximum, average and minimum values and a simple linear
regression of the three parameters for two different stations
for approximately a three year period. Hourly values have
been averaged for each month. Figure l(a) is data collected
at Mt. Tokusagamine in Yamaguchi prefecture on the
southern tip of Honshu, the main island of Japan, while the
measurements in Figure l(b) are from the Amami station,
located on a small island several degrees to the south of
Kyushu island. The former station shows a small uniform
increase in the average values as well as the maximum and
minimum values. This station is at an elevation of about 500
(m) above sea level and its geographic location makes it
susceptible to influences of transport of anthropogenic
precursors of ozone such as nitrogen oxides and of ozone
itself. The remoteness of the Amami station most likely
keeps it away from much anthropogenic influence. Figure
l(b) shows a very slight decrease in all three indices but
there is a gap in the data from the summer of 1986 to spring
of 1987 which is not taken into account. Though the
maximum hourly value of the month has decreased with time
the trend is not statistically significant.
The seasonal variation for these two stations is
common to all the other background stations in Japan
showing a peak in the spring and a minimum in the summer.
Amami reaches its peak in late March or early April while
Yamaguchi has its peak in late April/ early May. The
maximum in spring is slightly earlier compared to similar
stations in the eastern United States and western Europe
which usually have their maximums in late spring and
summer (Logan, 1989). Some have attributed this relatively
early spring maximum to natural peaks in the stratospheric
intrusion process during this season (Ogawa and Miyata,
1984). The higher frequency of stratospheric-tropospheric
exchange during this season bring higher ozone
concentrations into the upper troposphere. Others claim a
photochemical explanation (Liu et al., 1987). Colder
temperatures during winter and early spring allow for longer
transport distances and accumulation for ozone and its
precursors followed by peaks in concentration due to
warmer temperatures and increased photochemical activity.
The summer minimum may be possibly attributed to a shift
in the dominant meteorology over the region from
continental northeasterly winds from China brought on by
the Aleutian low-pressure system in the winter season to
https://ntrs.nasa.gov/search.jsp?R=19950004190 2020-06-16T11:46:40+00:00Z
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(a) (b)
Figure 1. (a) Monthly maximum, average and minimum surface ozone values for
Yamaguchi Station. Elevation : 530 (m) (b) Monthly maximum, average and
minimum surface ozone values for Amami Station. Elevation : 3(10 (m)
mostly southerly winds bringing moist air from the lower
latitudes in the summer (Whelpdale and Moody, 1990).
Figure 2(a) shows a plot of daily average ozone and
temperature at Happo in the heart of Japan for a period of
five months in 1987. The drop-off of the ozone
concentration in early July is very clearly shown while the
surface temperature continues to rise as the summer
develops. Happo is located at an elevation of about 1803
(m), essentially in the free troposphere, and the simultaneous
measurements of ozone, dust, temperature, pressure and
relative humidity is providing valuable insights into
deciphering the sources of ozone, whether it be local
sources, long range transport from urban centers, in situ
photochemical production, or downward transport from the
stratosphere and the upper troposphere. At this stage of the
analysis, positive correlations between ozone and dust
concentration peaks in the spring season, along with the
corresponding meteorological conditions, seem to show that
a combination of a passing cold front followed by general
subsidence under a stagnant high-pressure system over
Japan result in downward transport of ozone-rich, dust-rich
mid-troposphere air and increases in photochemical activity
causing higher production of ozone.
Similar plots for Amami and Yamaguchi (for years
1988 and 1986, respectively) are shown in Figure 2(b). As
discussed above, Amami reaches its spring peak sooner and
the summer minimum also arrives earlier, the latter most
likely due to its southerly location making it more susceptible
to relatively early influences from clean lower latitude air.
The overall values of ozone concentration arc lower for
Yamaguchi relative to Happo, and Amami tower still. Site
elevation and proximity to sources are the primary reasons
behind these differences.
3. SATELLITE ANALYSIS OF TROPOSPHERIC
COLUMN
To study the trends and regional distribution of the
entire tropospheric column in the western Pacific Rim,
satellite analyses have bccn performed utilizing the TOMS
instrument on board the Nimbus-7 satellite which measures
the total ozone column using back scattered UV-radiation
and the SAGE-II, charting the vertical distribution of ozone
in the stratosphere and above by the solar occultation
method, on the Earth Radiation Budget Satellite (Fishman
and Larsen, 1987). Data from the years of 1985-87 for the
region covering 20-50* N and 100-160" E have been
analyzed by subtracting the integrated SAGE-II
measurements above the tropopause from the total column
data provided by TOMS. It should be pointed out that
though the concept is very simple, there are still some
uncertainties in the actual implementation of this
methodology such as the accuracy of the TOMS instrument
itself (especially in the treatment of clouds), inherent
problems of the analysis such as the time difference of the
TOMS and SAGE-II measurements (kxzal n(xm versus local
sunrise/sunset), and application to the relatively unstable
midlatitude circulations, particularly with front and jet stream
activity.
Results show a peak for the tropospheric column in
East Asia in the spring and summer seasons of over 40
Dobson units as is seen in Figure 3 (averaged for all three
years). An accurate interpretation of the data is hampered by
the missing months of June and August, for which the
number of data points were too few to be considered
significant. However, it is clear that the tropospheric
column values for the summer season are much more
prominent when compared to the very low values obtained
from surface measurements during this season in Japan.
The regional distribution of the tropospheric column ozone
shows good correlation with the prevailing seasonal wind
patterns for the middle to upper troposphere. For example,
the seasonal peak k_ations are downwind of heavy (:mission
areas. There is also some evidence that the production and
transport of trotx_spheric ozone in the upper half and lower
half of the covered region of 20-50 ° N latitude are
predominantly governed by differently weighted
combinations of influencing factors, both meteorological and
phot¢_chemical. The relatively small number of o_erlapping
"points" between the two satellite instruments _s still a
substantial problem but with continued data collection
expanding the data base this methodology should prove
invaluable in studying the tropospheric column ozone
behavior in the upcoming years.
4. PRELIMINARY 3-DIMENSIONAL SIMULATION
The STEM-1I model (Carmichacl ctal., 1986) is
54 , , . g _,,.:
,o 1
(a)
....ii
l
(b)
Figure 2. (a) Daily averages of surface ozone and temperature at Happo station, elevation
1800 (m), during five months of 1987. The units for ozone is ppb and that for
temperature is *C. Ozone is the solid line and temperature is the dashed line.
(b) Daily averages of surface ozone for Amami (for 1988; solid line) and Yamaguchi
(for 1986; dashed line)
being utilized to conduct three-dimensional simulations of
tropospheric ozone transport, both horizontal and vertical,
and photochemistry in the study region of the western
Pacific Rim. The STEM-II is a comprehensive three-
dimensional, transport/chemistry /removal model. The
current version of the model uses the photochemical
mechanism of Lurmann et al. (1986), which includes 112
chemical reactions and 53 chemical species. This
mechanism is best suited for analysis of trace gas cycles
under conditions whcre NOx levels are > 0.1 ppb. In ordcr
to extend the mechanism to lower NOx conditions and to
explicitly include the role of isoprene chemistry this
mechanism has been modified as discussed in Jacob and
Wofsy (1988). The complete mechanism includes 70
species and 200 reactions. In addition to gas phase
phot(x:hemistry, the model treats cloud chemistry, and cloud
micro-physics. A dust transport and chemistry module has
been added to look more closely at thc problcm of "yellow
sand" transport that is quite prevalent in East Asia. This
phenomenon is thought to significantly influence the
atmospheric chemistry and trace gas budgets of this region.
Preliminary results show g(xx:l agreement between simulated
and observed data.
A springtime episode in May' of 1987 is uscd to
investigate the characteristics of tropospheric ozone
production and transport during this season, including
diurnal cycles. Figures 4 (a) and (b) show the results of a
preliminary simulation. Both figures display ozone
concentrations at surface level in ppb for thc fourth day' of
simulation, one at 8 AM and the other at 8 PM I(x:al time.
The first plot shows low values of surfacc ozone on the
continent while the pocket of high ozone lies in south central
Honshu with peak values of 80-1(X) pph This region of
high ozone moves to north central Japan after a 12-hour
period under the influence of a south-southeasterly wind and
also grows in size. Also prominent is the 50-80 ppb rcgion
on the northern Chinese coastal areas at this time. The peak
values in the early afternoon reaches values of over 100 ppb
for the simulation results. Finally, slightly' higher level
5O
4O
c 30
o
lO
1 2 3 4 5 6 7 8 9 10 11 12
Month
Figure 3. Monthly averages of tropospheric ozone residual
column values in Dobson units (2.69 x 10 ]6
molecules/cruZ). Averaged over the three 3,ears of 1985-
87. June and August missing due to insufficient data.
Overall region covered is 20-5,0°N and 100-160"E.
ozone concentrations reach 60-70 ppb at elevations of 1000
(m) above Japan while al:xwe the Chinese continent values of
_) ppb can be seen.
5. CONCLUDING REMARKS
Thc production and transport characteristics of
trol:x_spheric ozone in East Asia is being comprehensively
studied utilizing three different meth(x.ls. Each methodology
gives a different perspective of the phenomenon and together
they are adding to our insight of the tropospheric ozone
production, transport and destruction pathways. The
55
I-'---7 i
I1 / _- "
,,,tit__/ <
J
¢. f-
IfO ° [
1.5, i0 j
1.0,10 i
7.5.10'
5.0,1[1'
3.l].io'
(a) (b)
Figure 4. (a) Simulated results of surface ozone on 8 AM of May I l, 1987 (Day 4 of
simulation). (b) Simulated results of surface ozone on 8 PM of May I l, 1987 (Day 4
of simulation).
continuous monitoring of background surface ozone in
Japan is proving quite valuable and though the time span
covered is too short to state conclusively, a uniform trend in
either direction is not seen. Both downward transport of
ozone-rich upper atmosphere air and accumulation and
production of ozone and its precursors over the winter are
possible explanations for the consistent spring peak in ozone
concentration. However, the summer minimum is most
likely brought about by dynamic influences of the southerlies
dominating this season. Tropospheric column values show
high values for the summer season along with the spring.
The discrepancy in the summer may be caused by
differences in dynamic regimes. Finally, preliminary
simulations show that the model does a relatively good job in
following the movement of pockets of elevated ozone
concentrations. A more detailed and comprehensive
simulation is currently under way. Also, a more rigorous
statistical study of the satellite data is currently being
conducted and results of an in-depth look into the surface
ozone data is presented elsewhere (Sunwoo et al., 1992,).
Acknowledgments
The authors wish to acknowledge the contributions
made to this study by Dr. Hiromasa Ueda, Kyushu
University. The satellite ozone data and the surface ozone
data was obtained from the National Space Science Data
Center, USA and the National Institute of Environmental
Research, Japan. This research was supported in part by the
NASA Global Change Fellowship Program and NASA
Research Grant #NAGW-2428.
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Tropospheric ozone in the western Pacific Rim: Analysis of satellite and surface-based observations along with comprehensive 3-D model simulations

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