大気中の硫黄同位体分画の要因をPATMOモデルを用いて調査する

抄録

Sulfur isotopic fractionation coefficients in the atmosphere are the products of complex chemical reaction mechanisms. Therefore, understanding the atmospheric sulfur cycle requires a clear grasp of these underlying chemical processes. In this study, we aim to create and calibrate a one-dimensional photochemical model, PATMO [1], and use it to assess the sensitivity of modeled sulfur isotopic compositions to key isotopic fractionation parameters, including the effects of chemical reaction rates and various atmospheric processes on isotopic fractionation coefficients. We conduct budget analysis of COS, SO2, and sulfate, along with their isotopic composition (δ34S), and apply sensitivity simulations to evaluate the influence of different atmospheric processes and chemical pathways on sulfur isotopic fractionation.Our simulations reproduce the observed δ34S of tropospheric COS (~14‰) and reveal a progressive enrichment of δ34S in COS with increasing altitude due to photolytic removal in the stratosphere. This enrichment propagates to SO2 and subsequently to sulfate aerosols (SSA), with modeled δ34S values of ~2.6‰ for sulfate at 18-19 km, consistent with field measurements during vol