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Discussion papers
https://doi.org/10.5194/acp-2018-788
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2018-788
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 17 Aug 2018

Research article | 17 Aug 2018

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This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).

Vertical characterization of aerosol optical properties and brown carbon in winter in urban Beijing, China

Conghui Xie1,2, Weiqi Xu1,2, Junfeng Wang4, Qingqing Wang1, Dantong Liu5, Guiqian Tang1, Ping Chen6, Wei Du1,2, Jian Zhao1,2, Yingjie Zhang1, Wei Zhou1,2, Tingting Han1, Qingyun Bian2,7, Jie Li1, Pingqing Fu1,2, Zifa Wang1,2, Xinlei Ge4, James Allan5,8, Hugh Coe5, and Yele Sun1,2,3 Conghui Xie et al.
  • 1State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China
  • 2College of Earth Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
  • 3Center for Excellence in Regional Atmospheric Environment, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen 361021, China
  • 4School of Environmental Science and Engineering, Nanjing University of Information Science & Technology, Nanjing 210044, China
  • 5Centre for Atmospheric Science, School of Earth, Atmospheric and Environmental Science, University of Manchester, Manchester M13 9PL, UK
  • 6Handix Scientific LLC, Boulder, CO 80301, USA
  • 7CAS Key Laboratory of Regional Climate-Environment Research for Temperate East Asia, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China
  • 8National Centre for Atmospheric Science, The University of Manc hester, Manchester, UK

Abstract. Aerosol particles are of importance in the Earth’s radiation budget since they scatter and absorb sunlight. While extensive studies of aerosol optical properties have been conducted at ground sites, vertical measurements and characterization are very limited in megacities. In this work, we present simultaneous real-time online measurements of aerosol optical properties at ground level and at 260m on a meteorological tower from 16 November to 13 December in 2016 in Beijing along with measurements of continuous vertical profiles during two haze episodes. The average (±1σ) scattering and absorption coefficients (bsca and babs, λ=630nm) were 337.6 (±356.0) and 36.6 (±33.9)Mm−1 at 260m, which were 26.5% and 22.5% lower than those at ground level. Single scattering albedo (SSA), however, was comparable between the two heights with slightly higher values at ground level (0.89±0.04). Although bsca and babs showed overall similar temporal variations between ground and 260m, the ratios of 260m to ground varied substantially from less than 0.4 during the cleanest stages of haze episodes to >0.8 in the late afternoon. A more detailed analysis indicates that vertical profiles of bsca, babs, and SSA in the low atmosphere were closely related to the changes in meteorological conditions and mixing layer height. The mass absorption cross-section MAC of BC (λ=630nm) varied substantially from 9.5 to 13.2m2g−1 in winter in Beijing, and it was strongly associated with the mass ratio of non-refractory BC (rBC) materials to rBC (MR), and also the oxidation degree of organics in rBC-containing particles. Our results show that the increases in MAC of BC in winter were mainly caused by photochemically produced secondary materials. Light absorption of organic carbon (brown carbon, BrC) was also important in winter, which on average accounted for 46 (±8.5)% and 48 (±9.3)% of the total absorption at 370nm at ground level and 260m, respectively. A Linear regression model combined with positive matrix factorization analysis was used to show that coal combustion was the dominant source contribution of BrC (48–55%) followed by biomass burning (17%) and photochemically processed secondary organic aerosol (∼20%) in winter in Beijing.

Conghui Xie et al.
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Short summary
We present the first simultaneous real-time online measurements of aerosol optical properties at ground level and at 260 m on a meteorological tower in urban Beijing in winter. The vertical similarities and differences in scattering and absorption coefficients were characterized. The increases in MAC of BC were mainly associated with the coating materials on rBC. Coal combustion was the dominant source contribution of brown carbon followed by biomass burning and SOA in winter in Beijing.
We present the first simultaneous real-time online measurements of aerosol optical properties at...
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