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Hygroscopicity of Water‐Soluble PM 2.5 in Rural Northwest China: Contrasting Contributors Between Summer and Winter
Author(s) -
Chen Yukun,
Wang Xin,
Peng Huiying,
Li Jianjun,
Wang Yueshe,
Wang Gehui,
Li Jin,
Wu Can,
Liu Lang
Publication year - 2021
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
eISSN - 2169-8996
pISSN - 2169-897X
DOI - 10.1029/2021jd034977
Subject(s) - organic matter , relative humidity , sulfate , nitrate , environmental chemistry , chemistry , aerosol , particulates , chemical composition , mineralogy , environmental science , geography , meteorology , organic chemistry
In this study, we investigated the chemical composition and hygroscopicity of water‐soluble fraction in PM 2.5 collected from a rural site of Guanzhong Basin, a highly polluted region in northwest China. We found that inorganic components are the main substances promoting the hygroscopic properties of particulate matter (PH) in summer, while in winter, an increasing contribution from water‐soluble organic matters (WSOM) was observed. The sulfate‐nitrate‐ammonium concentration is higher on heavily polluted days, and a high concentration of water‐soluble organic matter was observed in non‐polluting days. Hygroscopic growth factors, g (RH), with elevated relative humidity (RH) of water‐soluble matter (WSM) were measured for 50, 75, 100, 125, 150 nm by hygroscopic tandem differential mobility analyzer. An initial dry particle diameter of 100 nm was chosen as the research object because the particle size has little effect on the hygroscopic growth factor at RH = 90%. The g (90%) WSM and κ WSM was in the range of 1.19–1.49 and 0.06–0.22 in summer, 1.24–1.49 and 0.08–0.22 in winter, respectively, which is similar to the hygroscopicity parameters of PH produced by biomass burning. The g (90%) WSOM and κ WSOM , obtained using E‐AIM model and Zdanovskii‐Stokes‐Robinson approach, were in the range of 1.06–1.69 and 0.02–0.36 in summer, 1.06–1.58 and 0.02–0.28 in winter, respectively. The hygroscopicity parameters of water‐soluble organic matter is close to the value of levoglucosan, an indicator of biomass burning, implying this region is highly affected by biomass burning. Overall, our results revealed that PM 2.5 in rural regions of Guanzhong Basin is mainly influenced by biomass burning.