Preprints
https://doi.org/10.5194/acp-2021-411
https://doi.org/10.5194/acp-2021-411

  06 Aug 2021

06 Aug 2021

Review status: this preprint is currently under review for the journal ACP.

Mixing state of refractory black carbon in fog and haze at rural sites in winter on the North China Plain

Yuting Zhang1,2, Hang Liu1,2, Shandong Lei1,2, Wanyun Xu3, Yu Tian1,2, Weijie Yao1,2, Xiaoyong Liu1,2,5, Qi Liao1,2, Jie Li1, Chun Chen1,2, Yele Sun1,2,5, Pingqing Fu4, Jinyuan Xin1,2,6, Junji Cao7, Xiaole Pan1, and Zifa Wang1,2,5 Yuting Zhang 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 and Planetary Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
  • 3State Key Laboratory of Severe Weather & Key Laboratory for Atmospheric Chemistry, Institute of Atmospheric Composition, Chinese Academy of Meteorological Sciences, Beijing, 100081, China
  • 4Institute of Surface–Earth System Science, Tianjin University, Tianjin 300072, China
  • 5Center for Excellence in Regional Atmospheric Environment, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen 361021, China
  • 6Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters, Nanjing University of Information Science and Technology, Nanjing 210044, China
  • 7Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China

Abstract. The variability of the mixing state of refractory black carbon aerosol (rBC) and the corresponding complicated light absorption capacity impose great uncertainty for its climate forcing assessment. In this study, field observations using a single particle soot photometer (SP2) were conducted to investigate the mixing state of rBC under different meteorological conditions at a rural site on the North China Plain. The results showed that the hourly mass concentration of rBC during the observation periods was 2.6 ± 1.5 µg m−3 on average with a moderate increase (3.1 ± 0.9) during fog episodes. The mass–equivalent size distribution of rBC exhibited an approximately lognormal distribution with a mass median diameter (MMD) of 213 nm. We found that the count median diameter (CMD) of rBC particles during snowfall episodes was obviously larger than that before–snowfall, indicating that smaller rBC–containing particles were much more effectively removed by snowfall. The droplet collision and Wegener–Bergeron–Findeisen (WBF) processes are possible explanations. Based on the Mie–scattering theory simulation, the relative and absolute coating thicknesses of rBC–containing particles were estimated to be 1.6 and ~52 nm for the rBC core with a mass–equivalent diameter (Dc) of 170–190 nm, respectively, indicating that the most of rBC–containing particles were thinly coated. Furthermore, moderate light absorption enhancement (Eabs = 1.3) and relatively low absorption cross–section (MAC = 5.5 m2/g) at 880 nm were observed at the GC site in winter compared with other typical rural sites.

The relationships between the microphysical properties of rBC and meteorological conditions were also studied. We found that the coatings of rBC–containing particles increase only when both ambient RH and secondary components increase at the same time, with the thickest coating during fog events and the thinnest on clean days. And −4 ~ 0 °C may be the most suitable temperature range for coating formation of rBC in this study. The sulfate formation from aqueous–phases reactions may have a limited contribution to Eabs under high RH conditions (RH > 80 %). The enhancement of Eabs of rBC–containing particles was strongly related to an increase in the mass fraction of nitrate instead of organics at appropriate temperature conditions.

Yuting Zhang et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2021-411', Anonymous Referee #2, 13 Aug 2021
  • RC2: 'Comment on acp-2021-411', Anonymous Referee #3, 20 Aug 2021
  • RC3: 'Comment on acp-2021-411', Anonymous Referee #1, 25 Aug 2021

Yuting Zhang et al.

Yuting Zhang et al.

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Short summary
In this study, the authors used a single particle soot photometer (SP2) to characterize the particle size, mixing state, and optical properties of black carbon aerosols in rural areas of North China Plain in winter. The author wishes to emphasize the importance of meteorological parameters on the mixing state of black carbon.
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