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Multi-scale model analysis of boundary layer ozone over East Asia

by M Lin, T Holloway, T Oki, D G Streets, A Richter
Atmospheric Chemistry and Physics ()
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Abstract

This study employs the regional Community Mul-tiscale Air Quality (CMAQ) model to examine seasonal and diurnal variations of boundary layer ozone (O 3) over East Asia. We evaluate the response of model simulations of boundary layer O 3 to the choice of chemical mechanisms, meteorological fields, boundary conditions, and model res-olutions. Data obtained from surface stations, aircraft mea-surements, and satellites are used to advance understanding of O 3 chemistry and mechanisms over East Asia and eval-uate how well the model represents the observed features. Satellite measurements and model simulations of summer-time rainfall are used to assess the impact of the Asian mon-soon on O 3 production. Our results suggest that summertime O 3 over Central Eastern China is highly sensitive to cloud cover and monsoonal rainfall over this region. Thus, accu-rate simulation of the East Asia summer monsoon is criti-cal to model analysis of atmospheric chemistry over China. Examination of hourly summertime O 3 mixing ratios from sites in Japan confirms the important role of diurnal boundary layer fluctuations in controlling ground-level O 3 . By com-paring five different model configurations with observations at six sites, the specific mechanisms responsible for model behavior are identified and discussed. In particular, vertical mixing, urban chemistry, and dry deposition depending on boundary layer height strongly affect model ability to capture observed behavior. Central Eastern China appears to be the most sensitive region in our study to the choice of chemical mechanisms. Evaluation with TRACE-P aircraft measure-ments reveals that neither the CB4 nor the SAPRC99 mech-Correspondence to: M. Lin (mlin26@wisc.edu) anisms consistently capture observed behavior of key pho-tochemical oxidants in springtime. However, our analysis finds that SAPRC99 performs somewhat better in simulating mixing ratios of H 2 O 2 (hydrogen peroxide) and PAN (per-oxyacetyl nitrate) at flight altitudes below 1 km. The high level of uncertainty associated with O 3 production in Central Eastern China poses a major problem for regional air quality management. This highly polluted, densely populated region would greatly benefit from comprehensive air quality moni-toring and the development of model chemical mechanisms appropriate to this unique atmospheric environment.

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