Articles | Volume 17, issue 5
Atmos. Chem. Phys., 17, 3659–3672, 2017
Atmos. Chem. Phys., 17, 3659–3672, 2017

Research article 15 Mar 2017

Research article | 15 Mar 2017

Volatility of mixed atmospheric humic-like substances and ammonium sulfate particles

Wei Nie1,2,3,8, Juan Hong3, Silja A. K. Häme3, Aijun Ding1,2,8, Yugen Li4, Chao Yan3, Liqing Hao5, Jyri Mikkilä3, Longfei Zheng1,2,8, Yuning Xie1,2,8, Caijun Zhu1,2,8, Zheng Xu1,2,8, Xuguang Chi1,2,8, Xin Huang1,2,8, Yang Zhou6,7, Peng Lin6,a, Annele Virtanen5, Douglas R. Worsnop3, Markku Kulmala3, Mikael Ehn3, Jianzhen Yu6, Veli-Matti Kerminen3, and Tuukka Petäjä3,1 Wei Nie et al.
  • 1Joint International Research Laboratory of Atmospheric and Earth System Sciences, Nanjing University, Nanjing, China
  • 2Institute for Climate and Global Change Research & School of Atmospheric Sciences, Nanjing University, Nanjing, 210023, China
  • 3Division of Atmospheric Sciences, Department of Physics, University of Helsinki, Helsinki, Finland
  • 4Division of Environment, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong SAR, China
  • 5Department of Applied Physics, University of Eastern Finland, Kuopio 70211, Finland
  • 6Department of Chemistry, Hong Kong University of Science & Technology, Clear Water Bay, Kowloon, Hong Kong SAR, China
  • 7Key Laboratory of Physical Oceanography, College of Oceanic and Atmospheric Sciences, Ocean University of China, Qingdao 266100, China
  • 8Collaborative Innovation Center of Climate Change, Jiangsu province, China
  • anow at: Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, WA 99532, USA

Abstract. The volatility of organic aerosols remains poorly understood due to the complexity of speciation and multiphase processes. In this study, we extracted humic-like substances (HULIS) from four atmospheric aerosol samples collected at the SORPES station in Nanjing, eastern China, and investigated the volatility behavior of particles at different sizes using a Volatility Tandem Differential Mobility Analyzer (VTDMA). In spite of the large differences in particle mass concentrations, the extracted HULIS from the four samples all revealed very high-oxidation states (O : C > 0.95), indicating secondary formation as the major source of HULIS in Yangtze River Delta (YRD). An overall low volatility was identified for the extracted HULIS, with the volume fraction remaining (VFR) higher than 55 % for all the regenerated HULIS particles at the temperature of 280 °C. A kinetic mass transfer model was applied to the thermodenuder (TD) data to interpret the observed evaporation pattern of HULIS, and to derive the mass fractions of semi-volatile (SVOC), low-volatility (LVOC) and extremely low-volatility components (ELVOC). The results showed that LVOC and ELVOC dominated (more than 80 %) the total volume of HULIS. Atomizing processes led to a size-dependent evaporation of regenerated HULIS particles, and resulted in more ELVOC in smaller particles. In order to understand the role of interaction between inorganic salts and atmospheric organic mixtures in the volatility of an organic aerosol, the evaporation of mixed samples of ammonium sulfate (AS) and HULIS was measured. The results showed a significant but nonlinear influence of ammonium sulfate on the volatility of HULIS. The estimated fraction of ELVOC in the organic part of the largest particles (145 nm) increased from 26 %, in pure HULIS samples, to 93 % in 1 : 3 (mass ratio of HULIS : AS) mixed samples, to 45 % in 2 : 2 mixed samples, and to 70 % in 3 : 1 mixed samples, suggesting that the interaction with ammonium sulfate tends to decrease the volatility of atmospheric organic compounds. Our results demonstrate that HULIS are important low-volatility, or even extremely low-volatility, compounds in the organic-aerosol phase. As important formation pathways of atmospheric HULIS, multiphase processes, including oxidation, oligomerization, polymerization and interaction with inorganic salts, are indicated to be important sources of low-volatility and extremely low-volatility species of organic aerosols.

Short summary
HULIS are demonstrated to be important low-volatility, or even extremely low volatility, compounds in the organic aerosol phase. This sheds new light on the connection between atmospheric HULIS and ELVOCs. The interaction between HULIS and ammonium sulfate was found to decrease the volatility of the HULIS part in HULIS-AS mixed samples, indicating multiphase processes have the potential to lower the volatility of organic compounds in the aerosol phase.
Final-revised paper