Changes in ground-level PM mass concentration and column aerosol optical depth over East Asia during 2004-2014

Abstract

Multi-year records of moderate resolution imaging spectroradiometer (MODIS), ground-based particulate matter mass concentration, cloud-aerosol lidar with orthogonal polarization (CALIOP), and ground-level lidar were analyzed to investigate seasonal and annual change of aerosol optical depth (AOD), Ångström exponent (Å), aerosol extinction coefficient, and particulate matter (PM10, PM2.5) mass concentration over East Asia. Least mean square (LMS) fit method is applied to detect the trends and their magnitudes for each selected regions and stations. Eleven-year MODIS measurements show mostly increasing AOD trend as well as Å trend, especially over the east coastal industrialized region in China, of 1.18 % yr-1 and 0.98 % yr-1, respectively. Seasonal and monthly variation of AOD show maximum value at April-July over East Asia, which were related to progress of summer monsoon rain band and stationary continental air mass on the northeast of Asia. Increasing trends of AOD were found for eight China stations (0.80 % yr-1), Seoul, Korea (0.40 % yr-1), but no trend were shown in Gosan station and decreasing trend was shown in Japan (-0.42 % yr-1). Decreasing PM10 mass concentration trend were shown in China, Korea, and Japan of -1.28 % yr-1, -2.77 % yr-1, and -2.03 % yr-1, respectively. Also, PM2.5 mass concentration show significant decreasing trend of about -1.16 % yr-1 over East Asia. Interestingly, significant decreasing trend in surface PM10 and PM¬2.5 mass concentration over China stations (-1.28 % yr-1) do not agreed well with the trends of MODIS-derived AOD (0.80 % yr-1). AOD estimated for planetary boundary layer (PBL-AOD) from CALIOP measurements over East China show decreasing trend of -1.71 % yr-1, wherever AOD estimated for free troposphere (FT-AOD) show increasing trend of 2.92 % yr-1. In addition, ground-level lidar in Seoul (SNU-L) show decreasing PBL-AOD trend of -2.57 % yr-1 and increasing FT-AOD trend of -0.40 % yr-1. This significant decreasing PBL-AOD and increasing FT-AOD trend is attributable to the relative contribution of complex processes that possibly include change in surface wind speed, total rainy days, atmospheric and hydrological cycle, and East Asian summer monsoon over East Asia.