Analysis of the seasonal variation of ozone in the boundary layer in East Asia using the Community Multi-scale Air Quality model: What controls surface ozone levels over Japan?

Ozone (O₃) concentrations in East Asia were simulated using the Community Multi-scale Air Quality model and their reproducibility was confirmed by comparing with observation data at Japanese monitoring sites. The model can reproduce the seasonal variation of surface O₃ over Japan. In particular, for the southern parts of Japan, simulated surface O₃ concentrations are strongly correlated with observations. Surface O₃ distribution over East Asia varies dynamically from season to season according to the meteorological condition. In May and June, 2-month average O₃ concentrations in the boundary layer are highest, 55-70 ppbv over East China and Japan at 35-40°N. We estimated the seasonal variation of the contribution of chemically produced O₃ by east Asian regional emissions. In the summertime, the contribution of the regional Asian emissions to O₃ concentrations is around 40-70% over most of China, and the highest is 60-70% (<35 ppbv) at the mouth area of Yantze River. This suggests that O ₃ concentrations over East Asia are strongly influenced by the chemical production by regional emissions during summer season. However, the inflow from outside of this model domain also contributes substantial O ₃ concentration over East Asia and its contribution is predominant in winter and early spring. The seasonal change of O₃ concentrations over Japan is characterized by two peaks in spring and autumn and summer minimum. The spring peak event in 2002 consists of split peaks: the first peak in Mar-Apr is mainly influenced by the inflow from outside of this model domain, the second spring peak between May and June is mainly influenced by chemically produced O₃ by regional emissions. During the summer season, O ₃ concentrations are the lowest over year because of the weak Asian outflow and northward penetration of the marine air mass.