Numerical simulation of the springtime transboundary air pollution in East Asia

During the spring, the high concentrations of ozone (O₃) and aerosols are frequently observed aloft in Japan. Such episodes supposedly are caused by the trans-boundary air pollution from other parts of East Asia. To confirm this hypothesis, an episode during the month of April 1993 is investigated by numerical simulations for East Asia with a regional meteorological model and a chemical transport model; the model can reproduce some of the key features of ozone and sulfate (SO₄^2-) aerosol concentrations, specifically, the time variations in ozone concentrations measured at several remote sites located in Japan and the day-to-day variations and vertical profiles for sulfate aerosol concentrations observed in Osaka. Model simulations show that (1) air pollutants such as sulfate aerosol, nitrate (NO₃^-) aerosol, and ozone are transported from the Asian continent to the Japanese Islands under synoptic meteorological conditions; (2) the trans-boundary pollutants increase urban air pollution in Japan; and (3) in the future, the air quality in Japan will be greatly impacted by increasing emissions in developing Asia.