Source attribution of Arctic black carbon constrained by aircraft and surface measurements

Black carbon (BC) contributes to Arctic warm- ing, yet sources of Arctic BC and their geographic con- tributions remain uncertain. We interpret a series of recent airborne (NETCARE 2015; PAMARCMiP 2009 and 2011 campaigns) and ground-based measurements (at Alert, Bar- row and Ny-Ålesund) from multiple methods (thermal, laser incandescence and light absorption) with the GEOS-Chem global chemical transport model and its adjoint to attribute the sources of Arctic BC. This is the first comparison with a chemical transport model of refractory BC (rBC) measure- ments at Alert. The springtime airborne measurements per- formed by the NETCARE campaign in 2015 and the PA- MARCMiP campaigns in 2009 and 2011 offer BC vertical profiles extending to above 6 km across the Arctic and in- clude profiles above Arctic ground monitoring stations. Our simulations with the addition of seasonally varying domes- tic heating and of gas flaring emissions are consistent with ground-based measurements of BC concentrations at Alert and Barrow in winter and spring (rRMSE < 13 %) and with airborne measurements of the BC vertical profile across the Arctic (rRMSE = 17 %) except for an underestimation in the middle troposphere (500–700 hPa). Sensitivity simulations suggest that anthropogenic emis- sions in eastern and southern Asia have the largest effect on the Arctic BC column burden both in spring (56 %) and annu ally (37 %), with the largest contribution in the middle tropo- sphere (400–700 hPa). Anthropogenic emissions from north- ern Asia contribute considerable BC (27% in spring and 43 % annually) to the lower troposphere (below 900 hPa). Biomass burning contributes 20 % to the Arctic BC column annually. At the Arctic surface, anthropogenic emissions from northern Asia (40–45 %) and eastern and southern Asia (20– 40 %) are the largest BC contributors in winter and spring, followed by Europe (16–36 %). Biomass burning from North America is the most important contributor to all stations in summ