Evaluation of biomass burning aerosols in the HadGEM3 climate model with observations from the SAMBBA field campaign
Atmospheric Chemistry and Physics
European Geosciences Union
© Author(s) 2016. CC Attribution 3.0 License
We present observations of biomass burning aerosol from the South American Biomass Burning Analysis (SAMBBA) and other measurement campaigns, and use these to evaluate the representation of biomass burning aerosol properties and processes in a state-of-the-art climate model. The evaluation includes detailed comparisons with aircraft and ground data, along with remote sensing observations from MODIS and AERONET. We demonstrate several improvements to aerosol properties following the implementation of the Global Model for Aerosol Processes (GLOMAP-mode) modal aerosol scheme in the HadGEM3 climate model. This predicts the particle size distribution, composition, and optical properties, giving increased accuracy in the representation of aerosol properties and physical–chemical processes over the Coupled Largescale Aerosol Scheme for Simulations in Climate Models (CLASSIC) bulk aerosol scheme previously used in HadGEM2. Although both models give similar regional distributions of carbonaceous aerosol mass and aerosol optical depth (AOD), GLOMAP-mode is better able to capture the observed size distribution, single scattering albedo, and Ångström exponent across different tropical biomass burning source regions. Both aerosol schemes overestimate the uptake of water compared to recent observations, CLASSIC more so than GLOMAP-mode, leading to a likely overestimation of aerosol scattering, AOD, and single scattering albedo at high relative humidity. Observed aerosol vertical distributions were well captured when biomass burning aerosol emissions were injected uniformly from the surface to 3 km. Finally, good agreement between observed and modelled AOD was gained only after scaling up GFED3 emissions by a factor of 1.6 for CLASSIC and 2.0 for GLOMAPmode. We attribute this difference in scaling factor mainly to different assumptions for the water uptake and growth of aerosol mass during ageing via oxidation and condensation of organics. We also note that similar agreement with observed AOD could have been achieved with lower scaling factors if the ratio of organic carbon to primary organic matter was increased in the models toward the upper range of observed values. Improved knowledge from measurements is required to reduce uncertainties in emission ratios for black carbon and organic carbon, and the ratio of organic carbon to primary organic matter for primary emissions from biomass burning.
The Facility for Airborne Atmospheric Measurement (FAAM) BAe-146 Atmospheric Research Aircraft is jointly funded by the Met Office and Natural Environment Research Council and operated by DirectFlight Ltd. We would like to thank the dedicated efforts of FAAM, DirectFlight, INPE, the University of São Paulo, and the Brazilian Ministry of Science and Technology in making the SAMBBA measurement campaign possible. For AERONET data we thank the PI investigators and their staff for establishing and maintaining the sites used in this investigation (Alta Floresta and Mongu: Brent Holben, Ilorin: Rachel T. Pinker, Chiang Mai: Serm Janjai, Bonanza Creek: John R. Van de Castle, Jabiru: Ross Mitchell). We thank Andrew Sayer and Robert Levy from Goddard Space Flight Centre for their advice with MODIS aerosol products. We thank Ville Vakkari for help in selecting data from the Welgegund station. James Haywood, Eoghan Darybshire, William Morgan, Hugh Coe, Graham Mann, and Nicolas Bellouin were funded by SAMBBA (NERC grant NE/J009822/1). Ben Johnson, James Haywood and Jane Mulcahy were funded under the Joint UK BEIS/DEFRA – Met Office Hadley Centre Climate Programme (GA01101). James Haywood was part funded by the IMPALA grant (NE/M017214/1) via Future Climates for Africa (FCA) funding provided by NERC and DFID
This is the final version of the article. Available from the publisher via the DOI in this record.
Published by Copernicus Publications on behalf of the European Geosciences Union.
Vol. 16, pp. 14657 - 14685