Mixing State of Black Carbon Aerosol in a Heavily Polluted Urban Area of China: Implications for Light Absorption Enhancement |
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| Authors: | Qiyuan Wang R-J Huang Yongming Han Gehui Wang Guohui Li |
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| Affiliation: | 1. Key Laboratory of Aerosol Science &2. Technology, SKLLQG, Institute of Earth Environment, Chinese Academy of Sciences, Xi’an, China;3. Laboratory of Atmospheric Chemistry, Paul Scherrer Institute, Villigen PSI, Switzerland;4. Centre for Climate and Air Pollution Studies, Ryan Institute, National University of Ireland Galway, Galway, Ireland |
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| Abstract: | Black carbon (BC) is important for climate forcing, and its effects on the Earth's radiative balance remain a major uncertainty in climate models. In this study, we investigated the mixing state of refractory black carbon (rBC) and aerosol optical properties in a polluted atmosphere at Xi’an, western China. The average rBC mass concentration was 9.9 μg m?3 during polluted periods, 7.6 times higher than that in clean periods. About 48.6% of the rBC was internally-mixed or coated with nonrefractory materials during polluted periods; this was 27% higher than in clean periods. Correlation analysis between the number fraction of thickly-coated rBC particles (fBC) and the major particulate species indicate that organics may be the primary contributor to rBC coatings during polluted periods. The average mass absorption cross section of rBC (MACBC) particles at λ = 870 nm was 7.6 ± 0.02 m2 g?1 for the entire campaign. The MACBC showed a positive correlation with fBC, and the enhancement of MACBC due to internal mixing was 1.8 times. These observations suggest that an enhancement of BC absorption by a factor of ～2 could be appropriate for climate models associated with high PM2.5 levels. Copyright 2014 American Association for Aerosol Research |
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