Preprints
https://doi.org/10.5194/acp-2018-367
https://doi.org/10.5194/acp-2018-367

  25 May 2018

25 May 2018

Status: this preprint has been retracted.

Aerosol acidity in a megacity with high ambient temperature and relative humidity of Central China: temporal variation, determining factors and pollution transition effect

Mingming Zheng1,2,3, Shaofei Kong2, Jianguo Bao1, Ke Xu3, Shurui Zheng2, Guowei Yang2, Jihong Quan3, Lianxin Yuan3, Nan Chen3, Yiping Tian3, Huang Zheng1,2, Jian Wu1,2, Dantong Liu4, Delong Zhao5, Qin Yan6, Tianliang Zhao6, and Shihua Qi1 Mingming Zheng et al.
  • 1Department of Environmental Science and Technology, School of Environmental Studies, China University of Geosciences (Wuhan), 430074, Wuhan, China
  • 2Department of Atmospheric Sciences, School of Environmental Studies, China University of Geosciences (Wuhan), 430074, Wuhan, China
  • 3Hubei Environment Monitoring Center, Wuhan, 430072, China
  • 4School of Earth, Atmospheric & Environmental Sciences, University of Manchester, UK
  • 5Beijing Weather Modification Office, Beijing 100089, China
  • 6Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters, Nanjing University of Information Science and Technology, Nanjing 210044, China

Abstract. Aerosol acidity affects the chemical transformation of aerosols and subsequent haze formation. High resolution (1-h) observation of water-soluble inorganic ions in fine particles, gaseous pollutants, and meteorological parameters was conducted from September 2015 to August 2016 at Wuhan, a megacity of Central China with high relative humidity and ambient temperature, compared with north Chinese cities. By adopting thermodynamic model ISOROPPIA-II, the aerosol acidity for different time scales, pollution episodes, and air mass directions was calculated. Aerosols in Wuhan were moderate acidic, with pH averaged as 3.30 ± 0.49. The aerosol acidity was higher in July (pH as 2.64 ± 0.31), September (pH as 2.75 ± 0.30) and August (pH as 2.79 ± 0.29), and lower in January (pH as 3.77 ± 0.28) and March (pH as 3.70 ± 0.16). It decreased with the air pollution increasing, with the pH values of 3.07 ± 0.45, 3.63 ± 0.27 and 3.84 ± 0.22 for clean, transition and polluted episodes, respectively. The air masses in Wuhan transported from North China exhibited higher aerosol acidity, with pH averaged as 3.17–3.22. The unique environmental and meteorological conditions (high humidity, annual averaged RH as 0.74 ± 0.13) lead to excess ammonium (on average of 6.06 ± 4.51 μg m−3) and abundant aerosol water content (AWC, on average of 71.0 ± 82.8 μg m−3) in Wuhan, which can explain the lower PM2.5 acidity in Wuhan than other megacities of China. At lower AWC level (less than ~ 15 μg m−3), the particle pH showed a decreasing trend with AWC increased. When the AWC continuous increased from ~ 15 to ~ 380 μg m−3, there was an obvious increase of particle pH. Then no significant growth of pH was found when AWC was higher than ~ 380 μg m−3. With atmospheric RH increasing, the aerosol pH exhibited decreasing trend firstly and then increased, with the turning point RH as about 0.48. There was a logarithmic growth of aerosol pH with total NHx (NH3 + NH4+) increasing. From the fitted logarithmic curve, the aerosol pH of Wuhan was at the range of pH rapid growth stage with NHx increasing, indicating that the control of ammonia emission in Wuhan could be an effective way to reduce the aerosol pH and further mitigate air pollution. This paper firstly obtained the aerosol acidity properties at a megacity under abundant ammonium and high humidity with high time-resolution, which is an important supplementary for the current aerosol acidity research around the world.

This preprint has been retracted.

Mingming Zheng et al.

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Mingming Zheng et al.

Mingming Zheng et al.

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This preprint has been retracted.

Short summary
In this paper, we study the aerosol acidity for different time scales, pollution episodes and air mass directions in a megacity of central China with high ambient temperature and relative humidity, and the impacting factors of pH were identified. This research is the first study concerning the aerosol acidity based on one-year online monitoring dataset with high resolution in central China, which is an important supplementary for the current aerosol acidity study around the world.
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