A climatology of aerosol optical depth over China from recent 10 years of MODIS remote sensing data

Using the recent 10-year (March 2000 to February 2010) MODIS data of aerosol optical depth (AOD), the distributions of annual and seasonal mean AOD over China are presented, and the trends and seasonal variations in AOD over 10 regions in China are analysed. The spatial pattern of annual mean AOD is characterized generally with two low centres and two high centres over China. Two low AOD centres are located in the areas with a high vegetation cover and a sparse population in (1) the high-latitude region in Northeast China with AOD of about 0.2 and (2) the high-altitude region in Southwest China with AOD from 0.1 to 0.2. These two low AOD centres are connected by a low AOD zone (0.2–0.3) in a northeast–southwest direction across China. Demarcated by this low AOD zone, two high centres with AOD of about 0.8 are situated in (1) the most densely populated and industrialized regions in China with high anthropogenic aerosols from North China Plain, Yangtze River areas covering Sichuan Basin, Central China and Yangtze River Delta to South China with Pearl River Delta region and (2) Tarim Basin in Northwest China with high natural aerosols dominated with desert dust. The spatial AOD patterns over China keep seasonally unchanged, but the strengths of the AOD-centres vary from season to season. The wintertime AOD is lowest in China. The monthly AOD variations from March to September in Southern China correspond with high AOD before, after the rain periods and low AOD during the rain periods of Asian summer monsoon. Asian summer monsoons also make a notable impact on the seasonal cycle of aerosols in China. The AOD in Northern China changes monthly with a single peak between April and June and a low in the winter months. The positive trends in AOD occur mostly in the aerosol source regions with higher annual mean AOD (>0.25), while the negative trends are found in the regions with lower annual mean AOD (<0.25) over China.

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