02 Nov 2022
02 Nov 2022
Status: this preprint is open for discussion.

Characteristics of Negative Cluster Ions in an Urban Environment 

Rujing Yin1,2,, Xiaoxiao Li1,3,, Chao Yan2,4, Runlong Cai2, Ying Zhou4, Juha Kangasluoma2, Nina Sarnela2, Janne Lampilahti2, Tuukka Petäjä2, Veli-Matti Kerminen2, Federico Bianchi2, Markku Kulmala2,4, and Jingkun Jiang1 Rujing Yin et al.
  • 1State Key Joint Laboratory of Environment Simulation and Pollution Control, School of Environment, Tsinghua University, Beijing, 100084, China
  • 2Institute for Atmospheric and Earth System Research/Physics, Faculty of Science, University of Helsinki, 00014 Helsinki, Finland
  • 3School of Resources and Environmental Sciences, Wuhan University, 430072 Wuhan, China
  • 4Aerosol and Haze Laboratory, Beijing Advanced Innovation Center for Soft Matter Science and Engineering, Beijing University of Chemical Technology, 100029 Beijing, China
  • These authors contributed equally to this work.

Abstract. Atmospheric cluster ions are important constituents in the atmosphere. Concentrations and compositions of cluster ions govern their effects on atmospheric chemistry, air quality, and human health. However, quantitative research on ion composition is rare, especially in an urban atmosphere where pollution levels and human populations are intense. In this study, we measure negative cluster ion compositions using an atmospheric pressure interface high-resolution time-of-flight mass spectrometer in urban Beijing. We demonstrate the feasibility of quantifying cluster ion compositions with simultaneous in-situ measurements by a neutral cluster and air ion spectrometer. The median concentrations of negative cluster ions smaller than 1.6 nm were 85 (61–112 for 25–75 %) cm-3, decreasing significantly with an increasing condensation sink (CS). These concentrations are far lower than those observed at comparatively clean sites due to the higher CS in polluted environments. The ions NO3- and HSO4-, together with organic ions with the adducts of NO3- and HSO4-, were the most abundant in urban Beijing, and the organic ions in the atmosphere were similar in composition to those oxygenated organic molecules charged in a chemical ionization mass spectrometer with NO3- as the reagent ions. It was shown that the ambient atmosphere is a natural ion-molecular reaction chamber with NO3- and HSO4- as the main reagent ions. Compared to the clean sites, negative cluster ions in Beijing are composed of more NO3- and CHON organic ions due to higher NOx concentrations and higher fractions of CHON molecules in overall oxygenated organic species. Using dynamic equilibrium equations to examine the fate of HSO4- and C3H3O4- in the atmosphere, we found that their main sources to be the ionization of H2SO4 and C3H4O4 by NO3- and their main loss being the condensational loss onto aerosol particles (73–75 %), followed by ion-molecule reaction losses (19 %), and ion-ion recombination losses (6–8 %).

Rujing Yin et al.

Status: open (until 28 Dec 2022)

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Rujing Yin et al.


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Short summary
The negative cluster ions with specific compositions are measured and quantified through the in-situ measurement of an atmospheric pressure interface high-resolution time-of-flight mass spectrometer and a neutral cluster and air ion spectrometer in urban Beijing. The governing factors of atmospheric negative cluster ion concentration and composition at polluted urban sites are revealed and the fate of two representative ions in the urban atmosphere is characterized.