Fossil fuel combustion and biomass burning sources of global black carbon from GEOS-Chem simulation and carbon isotope measurements

• Published in: Atmospheric Chemistry and Physics
• Main Authors: L. Qi, S. Wang
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2019
• Subjects: Physics; QC1-999; Chemistry; QD1-999; Antarctic; Arctic; Canada; Pacific; The Antarctic; Antarc*; black carbon; Siberia
• Online Access: https://doi.org/10.5194/acp-19-11545-2019; https://doaj.org/article/dc1f96dbe28c4191bb3a3245dcac73bf

We identify sources (fossil fuel combustion versus biomass burning) of black carbon (BC) in the atmosphere and in deposition using a global 3-D chemical transport model GEOS-Chem. We validate the simulated sources against carbon isotope measurements of BC around the globe and find that the model reproduces mean biomass burning contribution ( f bb %) in various regions within a factor of 2 (except in Europe, where f bb is underestimated by 63 %). GEOS-Chem shows that contribution from biomass burning in the Northern Hemisphere ( f bb : 35±14 %) is much less than that in the Southern Hemisphere ( 50±11 %). The largest atmospheric f bb is in Africa ( 64±20 %). Comparable contributions from biomass burning and fossil fuel combustion are found in southern (S) Asia ( 53±10 %), southeastern (SE) Asia ( 53±11 %), S America ( 47±14 %), the S Pacific ( 47±7 %), Australia ( 53±14 %) and the Antarctic ( 51±2 %). f bb is relatively small in eastern Asia ( 40±13 %), Siberia ( 35±8 %), the Arctic ( 33±6 %), Canada ( 31±7 %), the US ( 25±4 %) and Europe ( 19±7 %). Both observations and model results suggest that atmospheric f bb is higher in summer (59 %–78 %, varying with sub-regions) than in winter (28 %–32 %) in the Arctic, while it is higher in winter (42 %–58 %) and lower in summer (16 %–42 %) over the Himalayan–Tibetan Plateau. The seasonal variations of Atmospheric f bb are relatively flat in North America, Europe and Asia. We conducted four experiments to investigate the uncertainties associated with biofuel emissions, hygroscopicity of BC in fresh emissions, the aging rate and size-resolved wet scavenging. We find that doubling biofuel emissions for domestic heating north of 45 ∘ N increases f bb values in Europe in winter by ∼30 %, reducing the discrepancy between observed and modeled atmospheric f bb from −63 % to −54 %. The remaining large negative discrepancy between model and observations suggests that the biofuel emissions are probably still underestimated at high latitudes. Increasing the fraction of thickly ...