Reduction of aerosol absorption in Beijing since 2007 from MODIS and AERONET

September 1, 2011 — Click on image to enlarge.

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The Multi-Angle Implementation of Atmospheric Correction (MAIAC) is a new MODIS algorithm providing aerosol and land reflectance properties. Validation of MAIAC AOT with AERONET data over Beijing, China, indicates two distinct periods: prior to ∼March 2007 (period I), MAIAC underestimates AOT by 10–20% at peak values. This bias mostly disappears in period II (Figs. 1-2). The regression slope, which is strongly controlled by absorption, increases from 0.94 to 0.99 for Terra, and from 0.91 to 1.0 for Aqua between periods I and II. Because MAIAC used the same aerosol model for the entire time period, this points to a change in aerosol properties. By matching regression slopes in two periods, we assessed an increase in the single scattering albedo (SSA) by ~0.01. An analysis of AERONET data for Beijing showed a negligible change in effective particle size, and an increase in SSA by 0.02 over 9 years at 88% confidence level (Fig.3). Our analysis links this change to the reduction of the local black carbon emissions due to broad scale measures of Chinese government to improve air quality in advance of the 2008 Olympic Games and a recession of 2008-2009 [Lyapustin et al., 2011]. This result is confirmed by the long-term chemical composition analysis [Okuda et al., 2011] and IASI CO data (Fig.4).

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