Abstract
East China is among the fastest developing area in Asia, where atmospheric aerosol loading is high due to heavy urban and industrial emission. The Moderate Resolution Imaging Spectroradiometer (MODIS) level 2 aerosol products (2000–2007) were used to study aerosol spatial and temporal distributions, as well as their variations with local meteorological conditions over East China. By combining Aerosol Optical Depth (AOD) and aerosol Fine Mode Fraction (FMF), we found that the urban/industrial aerosol and soil dust are possibly two dominant species over northern part, whereas continental and marine aerosols possibly dominate the southern part of East China. Both annual mean AOD and area with high AOD increased from 2000 to 2007, with the largest increase seen in Yangtze River Delta region (YRD). In summer, AOD in East China reached the maximum of about 0.8 in YRD, dominated by fine mode particles. The minimum AOD occurred in winter with mostly coarse mode particles. Local aerosol properties were analyzed in three typical zones: the northern dry zone (I), the central urban/industrial zone (II) and the southern natural background zone (III). Monthly mean AODs in zone I and II were above 0.5 throughout the entire year, with the maximum AOD in June. High FMFs in this period indicated heavy urban and industrial pollution. Monthly mean AODs and FMFs in zone III reached maximum of 0.51 in April and September (up to 90.7%) respectively. High AOD in spring in zone III appears mostly due to the long-range dust transport from the North.
Highlights
The Aerosol Optical Depth (AOD) maximum in summer over Yangtze River Delta region (YRD) is caused by an increase of anthropogenic aerosols, as well as a stagnant synoptic system dominated in the Asian continent, causing building up of pollutants
20 Seasonally spatial distributions in Moderate Resolution Imaging Spectroradiometer (MODIS) derived AOD from 2000 to 2007 showed that the AOD maximum appeared in summer over YRD, which is quite different from the conclusion by Liu et al (2003) who used the MODIS derived AOD from 2001 to 2002 and found the AOD maximum appeared in spring
We present results of aerosol spatial distributions, seasonal and inter-annual variabilities, and the influence of meteorological conditions on aerosol physical properties derived from MODIS over East China from 2000 to 2007
Summary
MODIS AOD retrieval over land employs primarily three spectral channels centred at 0.47, 0.66, and 2.1 μm. The retrieval algorithm had a choice of two fine modes, the “urban/industrial,” and the “biomass burning/developing world,” differing as to their refractive indices, single scattering albedos (SSA or ω0), and phase 10 functions Each of these aerosol types is comprised of two or more lognormal modes (Kaufman et al, 1997), with their optical properties based on a combination of laboratory studies and Sun photometer data (Remer and Kaufman, 1998). Though MODIS derived FMFs have 20 not been validated over large area on land, they provide a good indication of the type of aerosol (fine or coarse) that dominates the size distribution. In winter, this region is controlled by the Mongolia high pressure and the Aleutian low pressure, and influenced by frequent cold air invasion from the north. More than 50% of the annual precipitation occurs from April to July
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