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Abstract

We examine seasonal and geographical distributions of tropospheric ozone
production and mixing ratios over East Asia with a global
three-dimensional chemical transport model called Model of Ozone and
Related Tracers, version 1 (MOZART 1). Net ozone production within the
East Asian boundary layer exhibits three distinct seasonal cycles
depending on region (north of 20 degrees N, 5-20 degrees N and south of
5 degrees N). North of 20 degrees N, net ozone production over East Asia
from spring through autumn is found to have a maximum extending from 25
degrees N-40 degrees N and from central eastern China to Japan,
resulting from the strong emission and transport of anthropogenic O-3
precursors. In winter, maximum O-3 production in this region occurs
between 20 degrees N and 30 degrees N, This is a region of long-range
transport. Over the Indochina peninsula, between 5 degrees N and 20
degrees N, net O-3 production is controlled by the seasonal cycle
between wet and dry seasons and has a maximum at the end of the dry
season due to emissions from biomass burning. South of 5 degrees N, in
the true tropics, O-3 mixing ratios are relatively constant throughout
the year and do not exhibit a seasonal cycle. A spring-summer maximum of
net O-3 production is found throughout the troposphere in East Asia. We
estimate an annual net O-3 production in East Asia of 117 Tg/yr, Both
model results and analysis of measurements of O-3/CO correlations over
East Asia and Japan show strong variability as a function of both
photochemical activity and seasonal meteorology, and indicate ozone
export off the coast of East Asia in spring. An upper estimate of O-3
export from East Asia to the Pacific Ocean in the mid-1980s of 3.3
Gmol/d (58 Tg/yr) is obtained.