Geographical and Climatological Characterization of Aerosol Distribution in China

The demarcation line of China’s population geography,the Aihui-Tengchong Line or the internationally known"Hu Line"divides China into the east and west parts,based on differences in China's population,geography,climate and economy,all of which are closely associated with the aerosols over China.By using the aerosol optical depth(AOD) data of MODIS during 2000 to 2010,the geographical and climatological distributions of aerosols over China are presented,and the‘Hu Line"is found also to describe a geographic division of aerosols over China.On the east of"Hu Line"with high population densities in the low-elevation China,the monthly AOD varies from the peak(0.5) during March and June to the low of around 0.3 in November and December with an annual mean of about 0.45,mostly contributed by anthropogenic aerosols from the human activities.On the west of"Hu Line"with a sparse population in the high elevation regions,the AOD is dominated by the naturally emitted aerosols with an annual mean of 0.25 changing between the high(about 3.0) in the period of April to July and the low(0.2) from October to January.The positive and negative trends in annual AOD in 2000-2010 are respectively found in the regions on the east and west of"Hu Line".Asian monsoon has a notable impact on the interannual variability of aerosols over the east region by modulating the atmospheric transport and precipitation washout.Taking example of the AOD anomalies in July 2002 and 2003 for a weak and strong year of south Asian summer monsoon,compared to the 10-year mean value,the AOD values in a weak summer monsoon year(2002) were(0.3-0.6) higher and(0.2-0.4) lower respectively in south and north of Huaihe River.In a strong summer monsoon year(2003),the opposite AOD pattern to the weak summer monsoon year 2002 was distributed over the east region with negative(positive) AOD anomalies in south(north) of Huaihe River.The interannual aerosol variations in the west of"Hu Line"are strongly influenced by dust emission sources in the deserts.The dust weather processes control the natural dust emissions.The maximal AOD of 3.0 in the west China could be brought by the frequent dust storm events from April to July.