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

Using the recent 10 year(2001—2010) MODIS data of aerosol optical depth(AOD),the distributions of 10-year annual and seasonal mean AOD at 550 nm over China are presented,and the seasonal variations in AOD over 10 regions in China are analyzed.A 10-year climatology of AOD over China is constructed.The spatial pattern of annual mean AOD is characterized generally with two low value centers and two high value centers over China.Two low AOD centers are located in the areas with a high vegetation cover and a sparse population in(1) the high-latitude Heilongjiang and Inner Mongolia in Northeast China with the AOD of about 0.2 and(2) the high-altitude Sichuan,Yunnan and Xizang in Southwest China with the AOD from 0.1 to 0.2.These two low AOD centers are connected by a low AOD ozone(0.2-0.3)in a northeast-southwest direction across China.Beside this low AOD ozone,two high centers with the AOD of about 0.8 are situated in(1) the most densely populated and industrialized regions in China with high anthropogenic aerosols stretching from North China Plain,Sichuan Basin,Hubei-Hunan and Yangtze River Delta to South China with Pearl River Delta region and(2) Taklimakan desert and the surrounding area in Northwest China with high natural aerosols dominated by desert dust.The spatial structures of seasonal AOD pattern over China remain unchanged,but the strengths of AOD-centers vary seasonally.Seasonally averaged over China,the area of high AOD is biggest in spring followed by summer and autumn with the minimum in winter.The monthly AOD values in Southern China peak twice respectively from March to May and from August to September and drop between May and July accompanied by Asian summer monsoon rain belt movement from the south to north.The monthly AOD in Northern China change with a single peak in June and July and a low during November and February.Taking example of the AOD anomalies and meteorological data in July 2002 and 2003 for a weak and strong year of south Asian summer monsoon,compared to the 10-year mean,the monthly AOD spatial distribution and change pattern relates to monsoon,wind speed and direction,precipitation,temperature and humidity in mainland of China.