Analysis of summertime atmospheric transport of fine particulate matter in Northeast Asia

In Northeast Asia, the effect of long-range transport of air pollutants is generally pronounced in spring and winter, but can be important even in summer. This study analyzed summer-time atmospheric transport of elemental carbon (EC) and sulfate (SO₄ ^2-) with the Community Multiscale Air Quality (CMAQ) model driven by the Weather Research and Forecasting (WRF) model. The WRF/CMAQ modeling system was applied to regions ranging from Northeast Asia to the Greater Tokyo Area in Japan in summer 2007. In terms of EC, while the model simulated well the effect of long-range transport, the simulation results indicated that domestic emissions in Japan dominantly contributed (85%) to EC concentrations in the Greater Tokyo. In terms of SO₄ ^2-, the simulation results indicated that both domestic emissions (62%) and long-range transport from the other countries (38%) substantially contributed to SO₄ ^2- concentrations in the Greater Tokyo. Distinctive transport processes of SO₄ ^2- were associated with typical summer-time meteorological conditions in the study region. When a Pacific high-pressure system covered the main island of Japan, domestic emissions, including volcanic emission, dominantly contributed to SO₄ ^2- concentrations in the Greater Tokyo. When a high-pressure system prevailed over the East China Sea and low-pressure systems passed north of Japan, synoptic westerly winds associated with this pressure pattern transported a large amount of SO₄ ^2- from the continent to Japan. In addition, although heavy precipitation and strong wind decreased SO₄ ^2- concentrations near the center of a typhoon, peripheral typhoon winds occasionally played an important role in long-range transport of SO ₄ ^2-.