The climatology of surface ozone over East Asia was investigated at a wide range of latitudes by integrating continuous measurements from Japanese monitoring networks. Although a spring maximum and a summer minimum were observed at all seven remote stations, significant latitudinal differences in the seasonal cycles were found, particularly in spring. At low latitudes (20-30°N) the spring maximum appears in March, while it appears in April at high latitudes (40-50°N), and in May at middle latitudes (30-40°N). A regional-scale chemical transport model was applied to examine factors contributing to the latitudinal dependence observed. The model reproduces the latitudinal gradient and the overall seasonal variations well, and suggests that transport patterns of Asian continental outflow coupled with photochemistry result in latitudinal inhomogeneity over East Asia. These results highlight the key role of dynamical processes in modulating the amplitude and phase of the spring maximum in surface ozone.
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