Study On The Transboundary Transport Of Biomass Burning Emissions Over Indo-China And Its Influence To The Aerosol Optical Depth Over Southern China

Southeast Asia is one of the biomass burning hotspots of the world. Burning activities were intensive over Indo-China in spring every year. The emissions not only reduce local air quality, but also affect other countries and regions through transboundary transport.According to the comparison of anthropogenic and biomass burning emission inventories, comprehensive analysis of a variety of satellite borne detector of remote sensing data, such as MODIS, OMI, and CALIOP, combined with weather conditions, geographic information and mesoscale meteorological model calculation results, we get the regional distribution and seasonal variation of aerosol over South China, southwest and peripheral regions, and discuss the mechanism of pollutant transportation and the AOD effect of aerial transport to southern China.The MODIS fire hotpots averaged in March to April from 2010 to 2014 shows that the fire hotpots was intensive over northern Indo-China. Southern China and Indo-China locate in the East Asian monsoon region, and March to April of each year is the transition season. The five-year averaged wind field from 2010 to 2014 obtained from NCEP(National Centers for Environmental Prediction) shows that the wind direction was totally opposite between 1000 hPa and 700 hPa. The surface wind(1000 hPa) was easterly, while it was smooth westerly at 700 hPa(about 3 kilometers). And the distribution of five-year averaged MODIS AOD and OMI UVAI shows that there is a high value area extended from Burma, northern Thailand, northern Laos and northern Vietnam to Beibu Gulf, Guangdong Province and Guangxi Province.The aggregated five-year averaged CALIOP(Cloud-Aerosol LIdar with Orthogonal Polarization) Level 2 532 nm extinction profiles of northern Indo-China and its downwind areas – Beibu Gulf, southern Guangxi province and the Pearl River Delta show that aerosol loading was much higher in spring than in winter and summer over northern Indo-China, with high aerosol loading extending to 5 km in altitude, and aerosol loadings over the downwind areas – Beibu Gulf, southern Guangxi province and the Pearl River Delta were higher than other two seasons obviously, and peaked at 3 km. Especially over Beibu Gulf, the aerosol loading at high atmosphere was higher than at low level in spring, which meant that the aerosols at high level was transported from other regions rather than local emissions. Combined with the smooth westerly at high level, we can conclude that the biomass burning emissions over northern Indo-China could be transported to southern China through high westerly, and the main transport pathway was between 2 km and 5 km.CALIOP AOD over different height bins over Beibu Gulf, southern Guangxi Province and the Pearl River Delta show that the ratio of aerosol at high atmosphere in spring over the above-mentioned regions was much larger than other two seasons. And the ratio reached 60.4%, 45.3%, and 44.4% over Beibu Gulf, southern Guangxi province and the Pearl River Delta, respectively. These ratios reflect the degree to which biomass burning emissions over northern Indo-China affect the AOD over southern China by transport at high altitude.