Variability of SO sub(2) in an intensive fog in North China Plain: Evidence of high solubility of SO sub(2)

• Published in: Particuology Vol. 11; no. 1; pp. 41 - 47
• Main Authors: Zhang, Qiang, Tie, Xuexi, Lin, Weili, Cao, Junji, Quan, Jiannong, Ran, Liang, Xu, Wanyun
• Format: Journal Article
• Language: English
• Published: 01.02.2013
• Subjects: China, People's Rep; China, People's Rep., North China Plain
• ISSN: 1674-2001

A field experiment was conducted in an intensive fog event between November 5 and November 8, 2009, in a heavily SO sub(2)-polluted area in North China Plain (NCP), to measure SO sub(2) and other air pollutants, liquid water content (LWC) of fog droplets, and other basic meteorological parameters. During the fog period, the concentrations of SO sub(2) showed large variability, which was closely related to the LWC in the fog droplets. The averaged concentration of SO sub(2) 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 SO sub(2) suggested that a majority of SO sub(2) (about 70%-80%) had reverted from gas to aqueous phase on account of the high solubility of SO sub(2) 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 SO sub(2), thus suggesting that aqueous reaction of SO sub(2) in fog droplets might play some important role in enhancing the solubility of SO sub(2). To simplify the phenomenon, an aeffective solubility coefficienta is proposed in this study. This variability of SO sub(2) measurement during the extensive fog event provides direct evidence of oxidation of SO sub(2) 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.