Urban-scale analysis of the seasonal trend of stabilized-Criegee intermediates and their effect on sulphate formation in the Greater Tokyo Area

Abstract

We conducted an urban-scale analysis of the contribution of gas phase stabilized-Criegee intermediates (sCIs) to atmospheric sulphate aerosol (SO₄²⁻) formation across four seasons in the Greater Tokyo Area (GTA) using the regional chemical transport model, the community multiscale air quality modelling (CMAQ) system. We analysed the seasonal and temporal trend of sCI formation in three areas: Tokyo Bay (urban), suburban, and mountainous areas. In all three areas, the sCI concentrations were high in the morning (7 a.m.) and early evening (6 p.m.) owing to the high frequency of vigorous traffic activities causing intense alkene emissions. The results suggest that more than 90% of the sCIs generated in the target areas are consumed by the unimolecular decomposition of sCIs themselves or by reactions with water, which are consistent with estimates from previous kinetic analysis studies targeting other regions. The contribution of sCIs to SO₄²⁻ formation estimated in this study was a maximum of 0.25% in the rural area, which is approximately 10-fold lower than that of previous studies. The results of the sCI loss pathway analysis suggested that the unimolecular decomposition of sCIs and the reaction between sCIs and water contribute comparably to the loss of sCIs, which caused less of an effect of sCIs on SO₄²⁻ formation compared with that in previous studies.