A33D-0180
A Microphysics-Based Black Carbon Aging Scheme in a Global Chemical Transport Model: Constraints from HIPPO Observations
Wednesday, 16 December 2015
Poster Hall (Moscone South)
Cenlin He1, Qinbin Li2, Kuo-Nan Liou2, Ling Qi3, Shu Tao4, Joshua Peter Schwarz5,6 and David W Fahey6, (1)University of California Los Angeles, Los Angeles, CA, United States, (2)Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles, CA, United States, (3)Univ of California Los Angeles, Los Angeles, CA, United States, (4)Peking University, College of Urban and Environmental Sciences, Beijing, China, (5)Cooperative Institute for Research in Environmental Sciences, Boulder, CO, United States, (6)NOAA ESRL, Boulder, CO, United States
Abstract:
Black carbon (BC) aging significantly affects its distributions and radiative properties, which is an important uncertainty source in estimating BC climatic effects. Global models often use a fixed aging timescale for the hydrophobic-to-hydrophilic BC conversion or a simple parameterization. We have developed and implemented a microphysics-based BC aging scheme that accounts for condensation and coagulation processes into a global 3-D chemical transport model (GEOS-Chem). Model results are systematically evaluated by comparing with the HIPPO observations across the Pacific (67°S-85°N) during 2009-2011. We find that the microphysics-based scheme substantially increases the BC aging rate over source regions as compared with the fixed aging timescale (1.2 days), due to the condensation of sulfate and secondary organic aerosols (SOA) and coagulation with pre-existing hydrophilic aerosols. However, the microphysics-based scheme slows down BC aging over Polar regions where condensation and coagulation are rather weak. We find that BC aging is primarily dominated by condensation process that accounts for ~75% of global BC aging, while the coagulation process is important over source regions where a large amount of pre-existing aerosols are available. Model results show that the fixed aging scheme tends to overestimate BC concentrations over the Pacific throughout the troposphere by a factor of 2-5 at different latitudes, while the microphysics-based scheme reduces the discrepancies by up to a factor of 2, particularly in the middle troposphere. The microphysics-based scheme developed in this work decreases BC column total concentrations at all latitudes and seasons, especially over tropical regions, leading to large improvement in model simulations. We are presently analyzing the impact of this scheme on global BC budget and lifetime, quantifying its uncertainty associated with key parameters, and investigating the effects of heterogeneous chemical oxidation on BC aging.
