Differences in Model Performance and Source Sensitivities for Sulfate Aerosol Resulting from Updates of the Aqueous- and Gas-Phase Oxidation Pathways for a Winter Pollution Episode in Tokyo, Japan

Abstract

During the Japanese intercomparison study, Japan’s Study for Reference Air Quality Modeling (J-STREAM), it was found that wintertime SO42– concentrations were underestimated over Japan with the Community Multiscale Air Quality (CMAQ) modeling system. Previously, following two development phases, model performance was improved by refining the Fe- and Mn-catalyzed oxidation pathways and by including an additional aqueous-phase pathway via NO2 oxidation. In a third phase, we examined a winter haze period in December 2016, involving a gas-phase oxidation pathway whereby three stabilized Criegee intermediates (SCI) were incorporated into the model. We also included options for a kinetic mass transfer aqueous-phase calculation. According to statistical analysis, simulations compared well with hourly SO42– observations in Tokyo. Source sensitivities for four domestic emission sources (transportation, stationary combustion, fugitive VOC, and agricultural NH3) were investigated. During the haze period, contributions from other sources (overseas and volcanic emissions) dominated, while domestic sources, including transportation and fuel combustion, played a role in enhancing SO42– concentrations around Tokyo Bay. Updating the aqueous phase metal catalyzed and NO2 oxidation pathways lead to increase contribution from other sources, and the additional gas phase SCI chemistry provided a link between fugitive VOC emission and SO42– concentration via changes in O3 concentration.

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

“…, the unimolecular decomposition and reaction with (H 2 O) 2 , which may lead to an overestimation of the effect of the sCI reactions on SO 4 2− formation. 11 The contribution of the sCI reactions to the SO 4 2− formation reached a maximum of 5.0 ng m −3 (or 0.25% of the total SO 4 2− ), which is not critical to the total SO 4 2− concentration on the ground surface of the GTA region. As stated in the previous section, the calculated SO 4 2− underestimated the observed results in winter and spring seasons for Tokyo Bay and suburban regions by ∼50%.…”

“…The results suggested that the maximum contribution of sCIs to SO 4 2− formation accounts for 5.0 ng m −3 , which corresponds to 0.25% of the total SO 4 2− concentration, indicating lower effects of sCIs in the targeted domain compared with previous studies. 11,12 The difference in the results derives from the incorporation of unimolecular decomposition of sCIs and the reaction with (H 2 O) 2 in this study. The SO 4 2− formation from sCIs contributes to a 0.024% decrease in radiative forcing.…”

“…Regional chemical transport model calculations, including sCI reactions, were conducted to evaluate the sCI contribution to SO 4 2− formation. Itahashi et al 11,12 calculated the sCI contribution to SO 4 2− formation over a winter haze episode in the Greater Tokyo Area (GTA), Japan used the community multiscale air quality modelling (CMAQ) system and concluded that the sCI reactions have a contribution of SO 4 2− concentration enhancement. 11,12 Liu et al also reported that sCI reactions affected the SO 4 2− concentration during a persistent summer air pollution episode in Beijing–Tianjin–Hebei, China evaluated by a WRF-Chem model.…”

“…Itahashi et al 11,12 calculated the sCI contribution to SO 4 2− formation over a winter haze episode in the Greater Tokyo Area (GTA), Japan used the community multiscale air quality modelling (CMAQ) system and concluded that the sCI reactions have a contribution of SO 4 2− concentration enhancement. 11,12 Liu et al also reported that sCI reactions affected the SO 4 2− concentration during a persistent summer air pollution episode in Beijing–Tianjin–Hebei, China evaluated by a WRF-Chem model. 13 Several studies suggested that the reaction of sCIs with water would significantly affect SO 4 2− formation via the oxidation of SO 2 by sCIs by 1 to 10%, depending on which value is used for the rate constant of H 2 O reaction.…”

Comprehensive analyses of source sensitivities to and apportionments of PM<sub>2.5</sub> and ozone over Japan via multiple numerical techniques

“…In reality, different model configurations and inputs may be used to consider strategies. Itahashi et al (2019b) reported that source sensitivities can be changed by the regional chemical transport model with improved treatments for aqueous reactions.…”