Preprints
https://doi.org/10.5194/acp-2021-454
https://doi.org/10.5194/acp-2021-454

  05 Jul 2021

05 Jul 2021

Review status: a revised version of this preprint is currently under review for the journal ACP.

Characterizing the volatility and mixing state of ambient fine particles in summer and winter of urban Beijing

Lu Chen1, Fang Zhang1, Don Collins2, Jieyao Liu1, Sihui Jiang1, Jingye Ren1, and Zhanqing Li3 Lu Chen et al.
  • 1College of Global Change and Earth System Science, Beijing Normal University, Beijing 100875, China
  • 2Chemical and Environmental Engineering, University of California, Riverside, CA 92521, USA
  • 3Earth System Science Interdisciplinary Center and Department of Atmospheric and Oceanic Science, University of Maryland, College Park, MD, USA

Abstract. Understanding the volatility and mixing state of atmospheric aerosols is important for elucidating the formation of fine particles and to help determining their effect on environment and climate. In this study, the volatility of the fine particles is characterized by the size-dependent volatility shrink factor (VSF) for summer and winter in the urban area of Beijing using measurements of a volatility tandem differential mobility analyzer (VTDMA). We show the volatility of aerosols is always with one high-volatile and one less- or non-volatile mode both in the summer and winter. On average, the particles are more volatile in the summer (with mean VSF of 0.3) than in the winter (with mean VSF of 0.6). The outstanding high-volatile mode around noontime illustrates the role of nucleation in producing more volatile particles in the summer. We further retrieve the mixing state of the ambient fine particles from the size-resolved VSF and find that the non-black carbon (BC) particles that formed from nucleation processes accounted for 52–69 % of the total number concentration in the summer. While, particles containing a refractory core that is thought to be BC-containing particles dominate and contribute 67–77 % toward the total number concentration in the winter. The diurnal cycles of the retrieved aerosol mixing state for the summer further supports the conclusion that nucleation process is the main contributors to non-BC particles. In addition, the extent of aging of BC particles was characterized as the ratio of the BC diameter before and after heating at 300 °C (Dp/Dc), showing that the average ratio of ~2.2 in the winter is higher than the average of ~1.5 in the summer, which indicates that BC aging is more efficient in wintertime, with resulting differences in light absorption enhancement between cold and warm seasons.

Lu Chen 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-2021-454', Anonymous Referee #1, 04 Aug 2021
    • AC1: 'Reply on RC1', Fang Zhang, 12 Aug 2021
  • RC2: 'Comment on acp-2021-454', Anonymous Referee #2, 14 Aug 2021
    • AC2: 'Reply on RC2', Fang Zhang, 20 Aug 2021

Lu Chen et al.

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Short summary
Understanding the volatility and mixing state of atmospheric aerosols is important for elucidating their formation. Here, the size-resolved volatility of fine particles is characterized using field measurements. On average, the particles are more volatile in the summer. The retrieved mixing state shows that black carbon (BC)-containing particles dominate and contribute 67–77 % toward the total number concentration in the winter. While the non-BC particles accounted for 52–69 % in the summer.
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