The mass-independent oxygen isotope composition in sulfate aerosol-a useful tool to identify sulfate formation: a review

2021 
Abstract Sulfate (SO42-) aerosol imparts numerous influences on the atmosphere, climate and earth. However, current models generally fail to accurately predict sulfate production because of incomplete knowledge of chemical formation pathways of sulfate. A mass-independent oxygen isotopic composition (Δ17O) has been suggested to be a useful tool to identify sulfate aerosol formation pathways. In this review, we focus on Δ17O in sulfate aerosol, which brings new insight into sulfate formation, sulfur cycle and atmospheric chemistry. The basic definitions and concepts of Δ17O as well as its ubiquity in nature are presented. The analytical methods utilized for studying oxygen isotopic composition of sulfate aerosol and sources of mass-independent sulfate oxygen isotopic composition are manifested. Observations of Δ17O in sulfate aerosol are discussed, which generally exhibits a seasonal trend with minimum values ranging from 0.4‰ to 0.9‰ in summer and maximum values in a range of 1.6‰-3.4‰ in winter among year-long measurements. Moreover, Δ17O in sulfate aerosol shows regional characteristics in which non-sea-salt sulfate aerosol in the most reported marine boundary layers possesses high values about 7‰. Stratospheric volcanic sulfate has Δ17O values high up to 4.8‰. Δ17O in sulfate aerosol represents good observational constraint on atmospheric and climatic models, and thus enable quantitative assessments of the relative importance of different formation pathways of sulfate aerosol.
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