Controlling factors of spatiotemporal variations in black carbon concentrations over the Arctic region by using a WRF/CMAQ simulation on the Northern Hemisphere scale

Black carbon (BC) aerosol, released into the atmosphere from fuel combustion and biomass burning, is known to be an important short-lived climate forcer (SLCF) because it efficiently absorbs solar radiation and directly heats the atmosphere. Because its accumulation on snow and ice promotes their melting, BC is an important driver of warming, particularly in the Arctic region. Observed surface BC concentrations in the Arctic region show typical seasonal variations, increasing during the winter and spring and decreasing during the warmer season with some peak events in few months of summer, along with large interannual variations. The present study investigates the primary factors influencing the differences in the spatiotemporal surface concentrations of BC in the Arctic region by performing a hemispheric-scale air-quality simulation for the years 2015 and 2016. The model reasonably simulates the observed BC concentration levels and their seasonal patterns, as well as their differences between these two years. This study shows that large year-to-year variability in BC-rich air-mass pathways, such as long-range transport from surrounding regions, and besides these air-mass stagnation within the Arctic region, influence the differences in the Arctic BC concentrations between 2015 and 2016. In addition, the Arctic BC concentrations were also controlled by interannual variations in the amount and distribution of emissions due to the size and the location of open fires, including both Asian crop residue burning in spring and boreal forest fires in summer.