Articles | Volume 17, issue 16
Atmos. Chem. Phys., 17, 9885–9896, 2017

Special issue: Regional transport and transformation of air pollution in...

Atmos. Chem. Phys., 17, 9885–9896, 2017

Research article 23 Aug 2017

Research article | 23 Aug 2017

Chemical composition and droplet size distribution of cloud at the summit of Mount Tai, China

Jiarong Li1, Xinfeng Wang1, Jianmin Chen1,2,3, Chao Zhu1, Weijun Li1, Chengbao Li2, Lu Liu1, Caihong Xu1, Liang Wen1, Likun Xue1, Wenxing Wang1, Aijun Ding3, and Hartmut Herrmann2,4 Jiarong Li et al.
  • 1Environment Research Institute, School of Environmental Science and Engineering, Shandong University, Ji'nan, 250100, China
  • 2Shanghai Key Laboratory of Atmospheric Particle Pollution and Prevention, Department of Environmental Science and Engineering, Institute of Atmospheric Sciences, Fudan University, Shanghai, 200433, China
  • 3Institute for Climate and Global Change Research, School of Atmospheric Sciences, Nanjing University, Nanjing, 210023, Jiangsu, China
  • 4Leibniz Institute for Tropospheric Research (TROPOS), Atmospheric Chemistry Department (ACD), Permoserstr. 15, 04318, Leipzig, Germany

Abstract. The chemical composition of 39 cloud samples and droplet size distributions in 24 cloud events were investigated at the summit of Mt. Tai from July to October 2014. Inorganic ions, organic acids, metals, HCHO, H2O2, sulfur(IV), organic carbon, and elemental carbon as well as pH and electrical conductivity were analyzed. The acidity of the cloud water significantly decreased from a reported value of pH 3.86 during 2007–2008 (Guo et al., 2012) to pH 5.87 in the present study. The concentrations of nitrate and ammonium were both increased since 2007–2008, but the overcompensation of ammonium led to an increase in the mean pH value. The microphysical properties showed that cloud droplets were smaller than 26.0 µm and most were in the range of 6.0–9.0 µm at Mt. Tai. The maximum droplet number concentration (Nd) was associated with a droplet size of 7.0 µm. High liquid water content (LWC) values could facilitate the formation of larger cloud droplets and broadened the droplet size distribution. Cloud droplets exhibited a strong interaction with atmospheric aerosols. Higher PM2. 5 levels resulted in higher concentrations of water-soluble ions and smaller sizes with increased numbers of cloud droplets. The lower pH values were likely to occur at higher PM2. 5 concentrations. Clouds were an important sink for soluble materials in the atmosphere. The dilution effect of cloud water should be considered when estimating concentrations of soluble components in the cloud phase.

Short summary
Cloud events at Mt. Tai were investigated for the chemical composition and size distribution of cloud droplets. An obvious rise in pH was found for elevated NH+4 during the last decade. Higher PM2.5 levels resulted in higher concentrations of water-soluble ions, smaller sizes and higher numbers of cloud droplets. The mechanism of cloud-droplet formation and the mass transfer between aerosol–gas–cloud phases were summarized to enrich the knowledge of cloud chemical and microphysical properties.
Final-revised paper