Characteristics of MERRA-2 black carbon variation in east China during 2000–2016

Abstract

The spatial-temporal distributions, historical trends and affecting factors of black carbon (BC) concentration both for the surface and atmospheric column in East China (110°E ~ 123°E, 23°N ~ 42°N) during 2000–2016 were investigated through MERRA-2 (Modern-era Retrospective Analysis for Research and Applications, Vision2) reanalysis data. Although a little overestimate at most inland stations and underestimate at most coastal ones, BC concentrations of MERRA-2 generally presented a good correlation (R = 0.83) compared with 598 monthly samples from ground-based observations at 14 stations. From the long-term records, the variation characteristics of BC surface concentration and column density over East China can be summarized as follow: The overall annual mean of BC surface concentration, column density and the concentration ratio of surface BC and PM2.5 (BC/PM2.5) over East China were 3.41 μg m−3, 3.78 mg m−2 and 8.71%, respectively. The highest annual mean (~6.00 μg m−3) and the fastest growth rate (~0.06 μg m−3•a−1) of surface concentration were both shown in the region of Beijing-Tianjin-Hebei (BTH) and Henan area. The seasonal mean BC surface concentrations of this region were between 5.00 and 9.00 μg m−3, with the highest in winter and the lowest in summer. As to column density, the highest annual mean (~6.00 mg m−2) and the fastest growth rate (~0.02 mg m−2•a−1) appeared in BTH and the border area of Hebei, Henan and Shandong. Unlike the surface concentration, the high-density center moved toward south and extended its coverage from summer to winter, but shrunk to north from winter to summer. The region of relatively high (14.00%–16.00%) BC/PM2.5 ratio was over BTH area and central Shanxi area, while the lowest (2.00%–6.00%) regions were in part of Inner Mongolia and south coastal area. The yearly BC concentration increased rapidly since 2000 and reached the peak in 2007. It decreased obviously in the south part of East China during 2008-2016. The BC/PM2.5 ratios experienced a “increase-decrease-increase” variation, with the maximum and minimum in 2005 and 2010, respectively.