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Radiative absorption enhancements due to the mixing state of atmospheric black carbon |
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| Authors: | Christopher D Cappa Timothy B Onasch Paola Massoli Douglas R Worsnop Timothy S Bates Eben S Cross Paul Davidovits Jani Hakala Katherine L Hayden B Tom Jobson Katheryn R Kolesar Daniel A Lack Brian M Lerner Shao-Meng Li Daniel Mellon Ibraheem Nuaaman Jason S Olfert Tuukka Petäjä Patricia K Quinn Chen Song R Subramanian Eric J Williams Rahul A Zaveri |
| Institution: | Department of Civil and Environmental Engineering, University of California, Davis, CA 95616, USA. cdcappa@ucdavis.edu |
| Abstract: | Atmospheric black carbon (BC) warms Earth's climate, and its reduction has been targeted for near-term climate change mitigation. Models that include forcing by BC assume internal mixing with non-BC aerosol components that enhance BC absorption, often by a factor of ~2; such model estimates have yet to be clearly validated through atmospheric observations. Here, direct in situ measurements of BC absorption enhancements (E(abs)) and mixing state are reported for two California regions. The observed E(abs) is small-6% on average at 532 nm-and increases weakly with photochemical aging. The E(abs) is less than predicted from observationally constrained theoretical calculations, suggesting that many climate models may overestimate warming by BC. These ambient observations stand in contrast to laboratory measurements that show substantial E(abs) for BC are possible. |
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