Characteristics of MERRA-2 Black Carbon Variation in East China

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 PM_2.5 (BC/PM_2.5) over East China were 3.41μg•m^-3, 3.78mg•m^-2 and 8.71%, respectively. The highest annual mean (~6.00μg•m^-3) and the fastest growth rate (~0.06μg•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 6.00-10.00μg•m^-3, with the highest in winter and the lowest in summer. As to column density, the highest annual mean (~6.00mg•m^-2) and the fastest growth rate (~0.02mg•m^-2•a^-1) appeared in the area from central Hebei to central Henan and the junctions of BTH and north Shandong region. 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/PM_2.5 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. During 2008-2016, BC concentration showed decreasing tendency in overall, significantly in the areas beneath latitude around 34°N. The BC/PM_2.5 ratios experienced a “increase-decrease-increase” variation, with the maximum and minimum in 2005 and 2010, respectively.