Variability of SO2 in an intensive fog in North China Plain: Evidence of high solubility of SO2--颗粒学报PARTICUOLOGY

Zhang, Q., Tie, X., Lin, W., Cao, J., Quan, J., Ran, L., & Xu, W. (2013). Variability of SO2 in an intensive fog in North China Plain: Evidence of high solubility of SO2. Particuology, 11(1), 41–47. https://doi.org/10.1016/j.partic.2012.09.005

Variability of SO₂in an intensive fog in North China Plain: Evidence of high solubility of SO₂

Qiang Zhang ^a, Xuexi Tie ^{b c *}, Weili Lin ^d, Junji Cao ^b, Jiannong Quan ^a, Liang Ran ^e, Wanyun Xu ^e

a Beijing Weather Modification Office, Beijing, China
b Key Laboratory of Aerosol, SKLLQG, Institute of Earth Environment, Chinese Academy of Sciences, Xi’an, China
c National Center for Atmospheric Research, Boulder, CO, USA
d Chinese Academy of Meteorological Science, Beijing, China
e Department of Atmospheric and Oceanic Sciences, School of Physics, Peking University, Beijing, China

10.1016/j.partic.2012.09.005

Volume 11, Issue 1, February 2013, Pages 41-47

Received 29 January 2012, Revised 27 August 2012, Accepted 12 September 2012, Available online 9 January 2013.

E-mail: xxtie@ucar.edu; tiexx@ieecas.cn

Highlights

► A field experiment was conducted in a heavily SO₂ polluted area located in the North China Plain.

► Large variability of SO₂ was observed to be related with fog events.

► Using only effective Henry's Law constant greatly underestimates reduction of SO₂concentrations.

► To account for effect of aqueous reactions significantly improves calculated SO₂ concentration.

Abstract

A field experiment was conducted in an intensive fog event between November 5 and November 8, 2009, in a heavily SO₂-polluted area in North China Plain (NCP), to measure SO₂ and other air pollutants, liquid water content (LWC) of fog droplets, and other basic meteorological parameters. During the fog period, the concentrations of SO₂ showed large variability, which was closely related to the LWC in the fog droplets. The averaged concentration of SO₂ during non-fog periods was about 25 ppbv, while during the fog period, it rapidly reduced to about 4–7 ppbv. Such large reduction of SO₂ suggested that a majority of SO₂ (about 70%–80%) had reverted from gas to aqueous phase on account of the high solubility of SO₂ in water in the fog droplets. However, the calculated gas to aqueous phase conversion was largely underestimated by merely using the Henry's Law constant of SO₂, thus suggesting that aqueous reaction of SO₂ in fog droplets might play some important role in enhancing the solubility of SO₂. To simplify the phenomenon, an “effective solubility coefficient” is proposed in this study. This variability of SO₂measurement during the extensive fog event provides direct evidence of oxidation of SO₂ in fog droplets, thus providing important implications for better understanding of the acidity in clouds, precipitation, and fogs in NCP, now a central environmental focus in China due to its rapid economic development.

Graphical abstract

Keywords

Solubility of SO₂; Fogs in the North China Plain; Aqueous phase reactions

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