Significant impact of water-soluble organic matter on hygroscopicity of fine particles under low relative humidity condition

Jun Tao; Zhisheng Zhang; Leiming Zhang; Yunfei Wu; Zhijun Wu; Fuli Nie; Laiguo Chen; Boguang Wang

doi:10.1016/j.scitotenv.2023.167980

Significant impact of water-soluble organic matter on hygroscopicity of fine particles under low relative humidity condition

Sci Total Environ. 2024 Jan 10:907:167980. doi: 10.1016/j.scitotenv.2023.167980. Epub 2023 Oct 21.

Authors

Jun Tao¹, Zhisheng Zhang², Leiming Zhang³, Yunfei Wu⁴, Zhijun Wu⁵, Fuli Nie², Laiguo Chen², Boguang Wang⁶

Affiliations

¹ Institute for Environmental and Climate Research, Jinan University, Guangzhou, China. Electronic address: taojun@jnu.edu.cn.
² South China Institute of Environmental Sciences, Ministry of Ecology and Environmental, Guangzhou, China.
³ Air Quality Research Division, Science and Technology Branch, Environment and Climate Change Canada, Toronto, Canada.
⁴ Key Laboratory of Middle Atmosphere and Global Environment Observation, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China.
⁵ State Key Joint Laboratory of Environmental Simulation and Pollution Control, College of Environmental Sciences and Engineering, Peking University, Beijing, China.
⁶ Institute for Environmental and Climate Research, Jinan University, Guangzhou, China.

PMID: 37866599
DOI: 10.1016/j.scitotenv.2023.167980

Abstract

Uncertainties in estimating the hygroscopicity of bulk aerosols under conditions of low relative humidity (RH) or below the deliquescent RH (DRH) of aerosols remain to be significant, mainly due to the presence of water-soluble organic matter (WSOM). To quantify the contributions of WSOM to aerosol hygroscopicity and associated uncertainties, a field campaign was conducted to measure the hygroscopic growth curve (f(RH)) of bulk aerosols online, dominant chemical compositions in PM_2.5 online and offline, and size distributions of the dominant chemical compositions offline during the dry and wet seasons of 2019-2020 in urban Guangzhou of south China. Based on the measured f(RH), the hygroscopicity parameter (κ) of bulk aerosols (κ_-f(RH)) exhibits a logarithmic increase with increasing RH until RH reaches 69 %. Beyond this threshold, κ_-f(RH) increases very slowly with further increase of RH, reaching 0.32 ± 0.04 during the dry season and 0.31 ± 0.05 during the wet season. The κ of WSOM (κ_-WSOM) was further estimated to be 0.22 ± 0.03 and 0.13 ± 0.04 in the dry and wet seasons, respectively, when RH > 69 %. WSOM significantly affects κ_-f(RH) by retarding the deliquescence process of aerosols and altering the mass ratio of water-soluble inorganic salts (WSIS) to WSOM within the size range of 0.4-0.9 μm, especially under low RH conditions (<60 %). The κ_-f(RH) under low RH conditions was revised based on the logarithmic regression equation between RH and the ratio of measured κ_-f(RH) to estimated κ_-f(RH>69%). f(RH) of WSIS and WSOM were then corrected using the revised κ_-f(RH) under low RH conditions, which showed 22-31 % lower values than those produced by the IMPROVE formulas.

Keywords: Aerosol chemical composition; Aerosol deliquescence; Aerosol hygroscopicity; Hygroscopic growth curve; Hygroscopicity parameter.