The mass-independent oxygen isotopic composition in sulfate aerosol-a useful tool to identify sulfate formation: a review
2021
Zhao, Yan | Zhang, Yan-Lin | Sun, Runxia
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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