Global trends and drivers of black carbon in the atmosphere

Black Carbon (BC) aerosol threatens air quality and climate. Controlling BC requires a better understanding of the multiple factors contributing to the increase of its concentration in the atmosphere. In this article, we use gridded data from Modern-Era Retrospective Analysis for Research and Applications (MERRA-2) and Mann-Kendall and Theil-Sen tests to tease out the BC trends (1980-2015) worldwide. We also adopt a combination of Principal Component Analysis and regression analysis to determine the strength of BC prime drivers. BC levels have risen in many parts of South America, Africa, and Asia, whereas consistent downtrends are observed in Europe and Australia-Oceania. These trends are primarily driven by local anthropogenic and biomass-burning emissions. Meteorological factors such as atmospheric ventilation, precipitation, and temperature also influenced BC variability, though their influence was generally secondary. Hotspots with increasing BC trends (≥ + 10%) were detected in South Asia, Andean America, North-West North America, and South and East Africa. BC has decreased in part of Brazil, Bolivia, Paraguay, and northern Argentina, as well as in Central Africa. The substantial rise in anthropogenic emissions largely explains the increasing BC trends in parts of South America, Asia, and other developing regions. In some areas of South America and Australia, BC downtrends are linked to precipitation increasing and biomass-burning emissions decreasing. In the North-West of North America, biomass burning is the main contributor to the BC increase. The contrasting regional trends emphasize the need for region-specific emission control policies, especially in developing areas where anthropogenic continue to drive BC increase.