Tropical modulation of East Asia air pollution.

Understanding air pollution in East Asia is of great importance given its high population density and serious air pollution problems during winter. Here, we show that the day-to-day variability of East Asia air pollution, during the recent 21-year winters, is remotely influenced by the Madden-Julian Oscillation (MJO), a dominant mode of subseasonal variability in the tropics. In particular, the concentration of particulate matter with aerodynamic diameter less than 10 micron (PM) becomes significantly high when the tropical convections are suppressed over the Indian Ocean (MJO phase 5-6), and becomes significantly low when those convections are enhanced (MJO phase 1-2). The station-averaged PM difference between these two MJO phases reaches up to 15% of daily PM variability, indicating that MJO is partly responsible for wintertime PM variability in East Asia. This finding helps to better understanding the wintertime PM variability in East Asia and monitoring high PM days.