Preprints
https://doi.org/10.5194/acp-2020-939
https://doi.org/10.5194/acp-2020-939

  12 Oct 2020

12 Oct 2020

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

Secondary aerosol formation alters CCN activity in the North China Plain

Jiangchuan Tao1, Ye Kuang1, Nan Ma1, Juan Hong1, Yele Sun2,3,4, Wanyun Xu5, Yanyan Zhang1, Yao He2, Qingwei Luo1, Linhong Xie1, Hang Su6, and Yafang Cheng6 Jiangchuan Tao et al.
  • 1Institute for Environmental and Climate Research, Jinan University, Guangzhou, Guangdong 511443, China
  • 2State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China
  • 3College of Earth and Planetary Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
  • 4Center for Excellence in Regional Atmospheric Environment, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen 361021, China
  • 5State Key Laboratory of Severe Weather, Key Laboratory for Atmospheric Chemistry, Institute of Atmospheric Composition, Chinese Academy of Meteorological Sciences, Beijing, 100081, China
  • 6Multiphase Chemistry Department, Max Planck Institute for Chemistry, Mainz 55128, Germany

Abstract. The formation of secondary aerosols (SA, including secondary organic and inorganic aerosols, SOA and SIA) is the dominant source of aerosol particles in the North China Plain and has a significant impact on the variations of particle size distribution (PNSD) and hygroscopicity. Previous studies have shown that the mechanism of SA formation can be affected by relative humidity (RH), and thus has different influences on the aerosol hygroscopicity and PNSD under different RH conditions. Based on the measurements of size-resolved particle activation ratio (SPAR), hygroscopicity distribution (GF-PDF), PM2.5 chemical composition, PNSD, meteorology and gaseous pollutants in a recent field campaign McFAN (Multiphase chemistry experiment in Fogs and Aerosols in the North China Plain) conducted at Gucheng site from 16th November to 16th December in 2018, the influences of SA formation on CCN activity and CCN number concentration (NCCN) calculation under different RH conditions were studied. Measurements showed that during daytime the SA formation can lead to a significant increase of NCCN and a strong diurnal variation of CCN activity. During periods with minimum RH higher than 50 % in daytime (high RH conditions), SA formation significantly contributed to the particle mass/size changes in wide particle size range of 150 nm to 1000 nm, and lead to the increase of NCCN in particle size range of 200 nm to 300 nm while increase of particle mass concentration mainly in particle size larger than 300 nm. During periods with minimum RH lower than 30 % in daytime (low RH conditions), SA formation mainly contributed to the particle mass/size changes in particle size smaller than 300 nm and so did the increases of both NCCN and particle mass concentration. As a result, upon the same amount of mass increase through SA formation, the increase of NCCN is weaker under high RH conditions while stronger under low RH conditions. Moreover, the diurnal variations of aerosol mixing state (inferred from CCN measurements) due to SA formation was different under different RH conditions, which contributed one of the largest uncertainties in NCCN predictions. By applying aerosol mixing state estimated by number fraction of hygroscopic particles from measurements of particle hygroscopicity or mass fraction of SA from measurements of particle chemical compositions, the NCCN prediction was largely improved with relative deviations smaller than 30 %. This study highlights the impact of SA formation on CCN activity and NCCN calculation, which is of great significance for improving parameterization of SA formation in chemical-transport models and CCN predictions in climate models.

Jiangchuan Tao et al.

 
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Jiangchuan Tao et al.

Jiangchuan Tao et al.

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Short summary
The mechanism of Secondary Aerosol (SA) formation can be affected by relative humidity (RH) and has different influences on the particle CCN activity under different RH conditions. In the North China Plain, we find different responses of CCN activity and enhancements of CCN number concentration to SA formation under different RH conditions. In addition, variations of aerosol mixing state due to SA formation contributes one of the largest uncertainties in predicting CCN number concentration.
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