Contrasting source contributions of Arctic black carbon to atmospheric concentrations, deposition flux, and atmospheric and snow radiative effects

Black carbon (BC) particles in the Arctic contribute to rapid warming of the Arctic by heating the atmosphere and snow and ice surfaces. Understanding the source contributions to Arctic BC is therefore important, but they are not well understood, especially those for atmospheric and snow radiative effects. Here we estimate simultaneously the source contributions of Arctic BC to near-surface and vertically integrated atmospheric BC mass concentrations (M-BC_SRF and M-BC_COL), BC deposition flux (M-BC_DEP), and BC radiative effects at the top of the atmosphere and snow surface (R-EBC_TOA and R-EBC_SNOW) and show that the source contributions to these five variables are highly different. In our estimates, Siberia makes the largest contribution to M-BC_SRF, M-BC_DEP, and R-EBC_ SNOW in the Arctic (defined as >70 degrees N), accounting for 70 %, 53 %, and 41 %, respectively. In contrast, Asia's contributions to M-BC_COL and R-EBC_TOA are largest, accounting for 37% and 43 %, respectively. In addition, the contributions of biomass burning sources are larger (29 %-35 %) to M-BC_DEP, R-EBC_TOA, and R-EBC_SNOW, which are highest from late spring to summer, and smaller (5.9 %-17 %) to M-BC_SRF and M-BC_COL, whose concentrations are highest from winter to spring. These differences in source contributions to these five variables are due to seasonal variations in BC emission, transport, and removal processes and solar radiation, as well as to differences in radiative effect efficiency (radiative effect per unit BC mass) among sources. Radiative effect efficiency varies by a factor of up to 4 among sources (1471-5326Wg(-1)) depending on lifetimes, mixing states, and heights of BC and seasonal variations of emissions and solar radiation. As a result, source contributions to radiative effects and mass concentrations (i.e., R-EBC_ TOA and M-BC_COL, respectively) are substantially different. The results of this study demonstrate the importance of considering differences in the source contributions of Arctic BC among mass concentrations, deposition, and atmospheric and snow radiative effects for accurate understanding of Arctic BC and its climate impacts.