Spatial and temporal variations of aerosol optical depth in China during the period from 2003 to 2006

Spatial and temporal variations of aerosol optical depth (AOD, or τ) in China were investigated using MODIS-derived aerosol data for a period of 2003–2006. The geographical distribution patterns of 4-year mean AOD for total, τ0.55 (AOD at 0.55 μm), fine, τ0.55-fine, and coarse, τ0.55-coarse, aerosols over China were addressed. These results indicate that the distribution of aerosol was largely affected by population, urban/industrial activity, agricultural biomass burning, spring dust, topography and humidity. τ0.55-fine in eastern China is significantly higher than in western China. Distribution of τ0.55-coarse reflected the influence of spring dust and urban/industrial pollution. The overall AOD in summer was higher than that in winter due to strong photochemical reactions producing secondary aerosols. In northern China, dust contributed to the mean τ0.55 in spring months. In some places, aggregated precipitation in the summer months caused a pronounced drop in the temporal profile of AOD. Coal combustion, industrial emission and vehicle exhaust produced coarse aerosols, while fine aerosols are mainly dominated by secondary particles. Smoke from open-fire straw burning produced fine aerosols in the harvest season.