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DOI	10.5194/acp-21-2053-2021
	Effects of liquid-liquid phase separation and relative humidity on the heterogeneous oh oxidation of inorganic-organic aerosols: Insights from methylglutaric acid and ammonium sulfate particles
	Ki Lam H.; Xu R.; Choczynski J.; Davies J.F.; Ham D.; Song M.; Zuend A.; Li W.; Steve Tse Y.-L.; Chan M.N.
发表日期	2021
ISSN	1680-7316
起始页码	2053
结束页码	2066
卷号	21 期号:3
英文摘要	Organic compounds residing near the surface of atmospheric aerosol particles are exposed to chemical reactions initiated by gas-phase oxidants, such as hydroxyl (OH) radicals. Aqueous droplets composed of inorganic salts and organic compounds can undergo phase separation into two liquid phases, depending on aerosol composition and relative humidity (RH). Such phase behavior can govern the surface characteristics and morphology of the aerosols, which in turn affect the heterogeneous reactivity of organic compounds toward gas-phase oxidants. In this work, we used an aerosol flow tube reactor coupled with an atmospheric pressure ionization source (direct analysis in real time) and a high-resolution mass spectrometer to investigate how phase separation in model aqueous droplets containing an inorganic salt (ammonium sulfate, AS) and an organic acid (3-methylglutaric acid, 3-MGA) with an organic-to-inorganic dry mass ratio (OIR) of 1 alters the heterogeneous OH reactivity. At high RH, 3-MGA/AS aerosols were aqueous droplets with a single liquid phase. When the RH decreased, aqueous 3-MGA/AS droplets underwent phase separation at g 1/475 RH. Once the droplets were phase-separated, they exhibited either a core shell, partially engulfed or a transition from core shell to partially engulfed structure, with an organic-rich outer phase and an inorganic-rich inner phase. The kinetics, quantified by an effective heterogenous OH rate constant, was found to increase gradually from 1:01±0:02× 10-12 to 1:73±0:02×10-12 cm3 molec.-1 s-1 when the RH decreased from 88 % to 55 %. The heterogeneous reactivity of phase-separated droplets is slightly higher than that of aqueous droplets with a single liquid phase. This could be explained by the finding that when the RH decreases, higher concentrations of organic molecules (i.e., 3-MGA) are present at or near the droplet surface, which are more readily exposed to OH oxidation, as demonstrated by phase separation measurements and model simulations. This could increase the reactive collision probability between 3-MGA molecules and OH radicals dissolved near the droplet surface and secondary chain reactions. Even for phase-separated droplets with a fully established core shell structure, the diffusion rate of organic molecules across the organic-rich outer shell is predicted to be fast in this system. Thus, the overall rate of reactions is likely governed by the surface concentration of 3-MGA rather than a diffusion limitation. Overall, understanding the aerosol phase state (single liquid phase versus two separate liquid phases) is essential to better probe the heterogenous reactivity under different aerosol chemical composition and environmental conditions (e.g., RH). © 2021 Author(s).
语种	英语
来源期刊	Atmospheric Chemistry and Physics
文献类型	期刊论文
条目标识符	http://gcip.llas.ac.cn/handle/2XKMVOVA/168764
作者单位	Earth System Science Programme, Faculty of Science, Chinese University of Hong Kong, Hong Kong, Hong Kong; Department of Chemistry, University of California Riverside, Riverside, CA, United States; Department of Earth and Environmental Sciences, Jeonbuk National University, Jeollabuk-do, South Korea; Department of Atmospheric and Oceanic Sciences, McGill University, Montréal, QC, Canada; Department of Chemistry, The Chinese University of Hong Kong, Hong Kong, Hong Kong; Institute of Environment Energy and Sustainability, Chinese University of Hong Kong, Hong Kong, Hong Kong
推荐引用方式 GB/T 7714	Ki Lam H.,Xu R.,Choczynski J.,et al. Effects of liquid-liquid phase separation and relative humidity on the heterogeneous oh oxidation of inorganic-organic aerosols: Insights from methylglutaric acid and ammonium sulfate particles[J],2021,21(3).
APA	Ki Lam H..,Xu R..,Choczynski J..,Davies J.F..,Ham D..,...&Chan M.N..(2021).Effects of liquid-liquid phase separation and relative humidity on the heterogeneous oh oxidation of inorganic-organic aerosols: Insights from methylglutaric acid and ammonium sulfate particles.Atmospheric Chemistry and Physics,21(3).
MLA	Ki Lam H.,et al."Effects of liquid-liquid phase separation and relative humidity on the heterogeneous oh oxidation of inorganic-organic aerosols: Insights from methylglutaric acid and ammonium sulfate particles".Atmospheric Chemistry and Physics 21.3(2021).