Abstract
We refined the aqueous-phase sulfate (SO42−) production in the state-of-the-art Community Multiscale Air Quality (CMAQ) model during the Japanese model inter-comparison project, known as Japan’s Study for Reference Air Quality Modeling (J-STREAM). In Japan, SO42− is the major component of PM2.5, and CMAQ reproduces the observed seasonal variation of SO42− with the summer maxima and winter minima. However, CMAQ underestimates the concentration during winter over Japan. Based on a review of the current modeling system, we identified a possible reason as being the inadequate aqueous-phase SO42− production by Fe- and Mn-catalyzed O2 oxidation. This is because these trace metals are not properly included in the Asian emission inventories. Fe and Mn observations over Japan showed that the model concentrations based on the latest Japanese emission inventory were substantially underestimated. Thus, we conducted sensitivity simulations where the modeled Fe and Mn concentrations were adjusted to the observed levels, the Fe and Mn solubilities were increased, and the oxidation rate constant was revised. Adjusting the concentration increased the SO42− concentration during winter, as did increasing the solubilities and revising the rate constant to consider pH dependencies. Statistical analysis showed that these sensitivity simulations improved model performance. The approach adopted in this study can partly improve model performance in terms of the underestimation of SO42− concentration during winter. From our findings, we demonstrated the importance of developing and evaluating trace metal emission inventories in Asia.
Highlights
Three-dimensional air quality modeling, representing complex processes such as emissions, transport, chemical reactions, and deposition of air pollutants, is a well-established way to advance our understanding of the atmospheric environment
To identify the problem with the model in winter, we focused on model performance for Fe and Mn
The Japanese model inter-comparison study, J-STREAM, found that SO4 2− is generally well captured by models, it is underestimated during winter
Summary
Three-dimensional air quality modeling, representing complex processes such as emissions, transport, chemical reactions, and deposition of air pollutants, is a well-established way to advance our understanding of the atmospheric environment. Model inter-comparison studies are valuable for understanding the uncertainties in modeling and improving modeling performance. Based on the outcomes and experiences of Japanese projects, a model inter-comparison project called Japan’s. Study for Reference Air Quality Modeling (J-STREAM) has begun. J-STREAM have already been published [1]. J-STREAM aims to establish reference air quality modeling. Atmosphere 2018, 9, 132 for source apportionment and to formulate an effective strategy to suppress secondary air pollutants including particulate matter with diameters less than 2.5 μm (PM2.5 ) and photochemical ozone (O3 ), in Japan through model inter-comparison studies. The first-phase focuses on understanding the ranges and limitations of PM2.5 and O3 concentrations simulated by participants using common input datasets
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