Aerosol variability over East Asia as seen by POLDER space-borne sensors

This paper is devoted to analysis of aerosol distribution and variability over East Asia based on PARASOL/POLDER-3 aerosol products over land. We first compared POLDER-3 Aerosol Optical Depth (AOD) with fine modeAOD(particles radius <= 0.30 mu m) computed from AERONET (Aerosol Robotic Network) inversions over 14 sites. The rather good correlation (R approximate to 0.92) observed over land demonstrates the remarkable sensitivity of POLDER-3 retrievals to the smaller fraction of fine particles, mostly originating from anthropogenic sources. We analyzed the characteristics and seasonal variation of aerosol distribution over East Asia by considering 4 years of POLDER-3 Level 2 data (March 2005 to February 2009). Our study shows that the spatial distribution of fine-mode aerosols over East Asia, as retrieved from POLDER-3, is highly associated with human activities. Our work also evidenced a strong variability of seasonal fine-mode AOD patterns with geographical locations. Finally, the interannual variation during 2003-2009 periods of summer fine-mode AOD over North China, in particular the Beijing City region, was analyzed for the contribution to evaluating the regional impact of emission reduction enforced in Beijing during the 2008 Olympic Summer Games. We found that the summer average of fine-mode AOD exhibited relatively higher values in 2003, 2007, and 2008. The interannual variation patterns of monthly averaged AOD (June to August) shows that June generally exhibits the strongest variation and varies similarly to July, but differs from August. As a reference point, measured total AOD and fine-mode AOD computed from AERONET inversions in summer are also discussed for the Beijing City region.