Variation in MERRA-2 aerosol optical depth and absorption aerosol optical depth over China from 1980 to 2017

Abstract

4258 instantaneous 550 nm Aerosol Optical Depth (AOD) values were compared between the second Modern-Era Retrospective analysis for Research and Applications (MERRA-2) and the Aerosol Robotic Network (AERONET) in four seasons at 12 AERONET sites across China. The correlation coefficients (R) in spring, summer, autumn and winter were 0.88, 0.92, 0.91 and 0.87, respectively. The MERRA-2 AOD was compared with the Moderate resolution Imaging Spectroradiometer (MODIS/Aqua) AOD over China from 2003 to 2017, and good agreement was obtained. 4501 daily AOD values were compared between MERRA-2 and MODIS at 16 sites over China. Spatial distribution and temporal variation of MERRA-2 AOD over China were analyzed from 1980 to 2017. Mean values of MERRA-2 AOD indicated that high AOD mainly appeared in the eastern, southeastern and central China, while low AOD mostly occurred in the western and northeastern China. Mean AOD values over China during this study period in each month was also discussed, and similar spatial distribution (high AOD in developed areas, low AOD in rural and less developed areas) was found in each month. Slight AOD increase could be observed in the 1980s and 1990s, and a rapid increase happened from 2001 to 2010, followed by an AOD decrease between 2011 and 2017. Annual variation of mean AOD of the whole China (the Yangtze River Delta) showed a slight increase of 0.0010 (0.0045) per year from 1980 to 1999, a rapid increase of 0.0096 (0.0271) per year between 2000 and 2009, and a decrease of −0.0089 (−0.0206) per year from 2010 to 2017. Annual AOD Variation in Jing-jin-ji and Pearl River Delta is similar to that in the Yangtze River Delta. In four seasons, AOD change was similar to the annual AOD variation except winter with a slight decrease of −0.0012 per year between 1980 and 1999. AOD variation over China before and after the Pinatubo volcanic eruption in the Philippines in June 1991 was analyzed to get a better understanding of the transport and the impact on the environment from volcanic pollutants. AOD variation trend over China was studied in two periods. The increasing trend appeared in most part of China from 1980 to 2009, while a decreasing trend could be found in almost the entire China between 2010 and 2017. Spatial and temporal variation of MERRA-2 Absorption Aerosol Optical Depth (AAOD), Black Carbon Absorption Aerosol Optical Depth (BCAAOD) and Dust Absorption Aerosol Optical Depth (DUAAOD) were analyzed during the period between 1980 and 2017. BCAAOD (66.30%) and DUAAOD (30.56%) offered the major contribution to total AAOD in China. 38 years of variation of AAOD over China is mainly due to the variation of BCAAOD. BCAAOD experienced an increase (1980–2007) and a decrease (2008–2017) during the 38 years in China.