Impact of Anomalous East Asian Winter Monsoon on the Spatial Distribution of Aerosols over East Asia

Aerosol is one of the most significant air pollutants in East Asia. Its temporal and spatial distribution can be affected by the East Asia winter monsoon. Using the Moderate-resolution Imaging Spectroradiometer (MODIS) aerosol product and the National Center for Environmental Prediction (NCEP) reanalysis monthly meteorological field data between 2000 and 2014, this study statistically analyzes the variation trend of the East Asia winter monsoon (EAWM), the annual variation of the aerosol optical depth (AOD) over East Asia, and the effect of the anomalous EAWM on the distribution of aerosols. The analysis based on the aerosol product shows that the AOD values continually increase during the recent decade in the winter of East Asia with a maximum value of 0.44 in 2007. High values usually occur in the Sichuan Basin, the North China Plain, and most areas of the middle and lower reaches of Yangtze. With the aid of the EAWM index defined by the characteristics of the wind field, the EAWM is found to have strong interannual and interdecadal variations and exhibits a gradually decreasing trend. Results also show that the EAWM has a considerable effect on the spatial distribution of aerosols. In strong EAWM years, the stronger north wind can enhance the transportation of aerosols to the southern area and form the spatial distribution pattern of the north low and south high for the AOD over East Asia. However, in weak EAWM years, the transportation effect is weakened, resulting in the accumulation of more aerosols in the North China Plain and the formation of the AOD pattern of the north high and south low.