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The urban model inter-comparison study (UMICS) was conducted in order to improve the performance of air quality models (AQMs) for simulating fine particulate matter (PM2.5) in the Greater Tokyo Area of Japan. UMICS consists of three phases: the first phase focusing on elemental carbon (UMICS1), the second phase focusing on sulfate, nitrate and ammonium (UMICS2), and the third phase focusing on organic aerosol (OA) (UMICS 3). In UMICS2/3, all the participating AQMs were the Community Multiscale Air Quality modeling system (CMAQ) with different configurations, and they similarly overestimated PM2.5nitrate concentration and underestimated PM2.5OA concentration. Various sensitivity analyses on CMAQ configurations, emissions and boundary concentrations, and meteorological fields were conducted in order to seek pathways for improvement of PM2.5simulation. The sensitivity analyses revealed that PM2.5nitrate concentration was highly sensitive to emissions of ammonia (NH3) and dry deposition of nitric acid (HNO3) and NH3, and PM2.5OA concentration was highly sensitive to emissions of condensable organic compounds (COC). It was found that PM2.5simulation was substantially improved by using modified monthly profile of NH3emissions, larger dry deposition velocities of HNO3and NH3, and additionally estimated COC emissions. Moreover, variability in PM2.5simulation was estimated from the results of all the sensitivity analyses. The variabilities on CMAQ configurations, chemical inputs (emissions and boundary concentrations), and meteorological fields were 6.1–6.5, 9.7–10.9, and 10.3–12.3%, respectively.

The authors analyze the sensitivities of source regions in East Asia to PM2.5(particulate matter with an aerodynamic diameter of ≤2.5 µm) concentration at Fukue Island located in the western part of Japan by using a regional chemical transport model with emission sensitivity simulations for the year 2010. The temporal variations in PM2.5concentration are generally reproduced, but the absolute concentration is underestimated by the model. Chemical composition of PM2.5in the model is compared with filter sampling data in spring; simulated sulfate, ammonium, and elemental carbon are consistent with observations, but mass concentration of particulate organic matters is underestimated. The relative contribution from each source region shows the seasonal variation, especially in summer. The contribution from central north China (105°E–124°E, 34°N–42°N) accounts for 50–60% of PM2.5at Fukue Island except in summer; it significantly decreases in summer (18%). Central south China (105°E–123°E, 26°N–34°N) has the relative contribution of 15–30%. The contribution from the Korean Peninsula is estimated at about 10% except in summer. The domestic contribution accounts for about 7% in spring and autumn and increases to 19% in summer. We also estimate the relative contribution to daily average concentration in high PM2.5days (>35 μg m−3). Central north China has a significant contribution of 60–70% except in summer. The relative contribution from central south China is estimated at 46% in summer and about 30% in the other seasons. The contributions from central north and south China on high PM2.5days are generally larger than those of their seasonal mean contributions. The domestic contribution is smaller than the seasonal mean value in every season; it is less than 10% even in summer. These model results suggest that foreign anthropogenic sources have a substantial impact on attainment of the atmospheric environmental standard of Japan at Fukue Island.Implications: The contribution from several source regions in East Asia to PM2.5concentration at Fukue Island, a remote island located in the western part of Japan and close to the Asian continent, is estimated using a three-dimensional chemical transport model. The model results suggest that PM2.5that is attributed to foreign anthropogenic sources have a larger contribution than that of domestic pollution and have a substantial impact on attainment of the atmospheric environmental standard of Japan at Fukue Island.

NO2vertical column densities (VCDs) over East Asia in June and December 2007 were simulated by the Community Multi-scale Air Quality (CMAQ) version 4.7.1 using an updated and more elaborate version of the Regional Emission Inventory in Asia (REAS) version 2. The modeling system could reasonably capture observed spatiotemporal changes of NO2VCDs by satellite sensors, the Global Ozone Monitoring Experiment-2 (GOME-2), the Scanning Imaging Absorption Spectrometer for Atmospheric Cartography (SCIAMACHY), and the Ozone Monitoring Instrument (OMI), even at the coarsest horizontal resolution of 80 km. The CMAQ simulations were performed in a sequence of three horizontal resolutions (80 km, 40 km, and 20 km) for June and December 2007 to investigate the influence of changes of horizontal resolution on the obtained NO2VCDs. CMAQ-simulated NO2VCDs generally increased with improvements in resolution from 80 km to 40 km and then to 20 km. Increases in the CMAQ-simulated NO2VCDs were greater for the change from 80 km to 40 km than for those from 40 km and 20 km, in which the increases of NO2VCDs due to the improvement of horizontal resolution were approached convergence at the horizontal resolution of approximately 20 km. Conversely, no clear convergences in NO2VCDs changes were found at near Tokyo and over the East China Sea. The biases of the NO2VCDs simulated at a resolution of 20 km against the satellite retrievals were ∼36% near Beijing (CHN1) and ∼78% near Shanghai (CHN2) in summer; these errors were found to be comparable to the horizontal resolution-dependent errors, which were 18–25% at CHN1 and 44–58% at CHN2 from 80 km to 40 km. Conversely, the influence of changes of horizontal resolution in winter was relatively less compared to that in summer.Implications: NO2VCDs over East Asia in June and December 2007 were simulated using CMAQ version 4.7.1 and REAS version 2. The modeling system could reasonably capture observed spatiotemporal changes of NO2VCDs by satellite sensors. The CMAQ simulations were performed in a sequence of three horizontal resolutions, 80, 40, and 20 km, to investigate the influence of changes of horizontal resolution on the obtained NO2VCDs. The results suggested that the influence of changes of horizontal resolution was larger in summer compared to that in winter. The magnitude of the influence was comparable to the biases of the NO2VCDs simulated at a resolution of 20 km against the satellite retrievals.

Improvement of air quality models is required so that they can be utilized to design effective control strategies for fine particulate matter (PM2.5). The Community Multiscale Air Quality modeling system was applied to the Greater Tokyo Area of Japan in winter 2010 and summer 2011. The model results were compared with observed concentrations of PM2.5sulfate (SO42-), nitrate (NO3−) and ammonium, and gaseous nitric acid (HNO3) and ammonia (NH3). The model approximately reproduced PM2.5SO42−concentration, but clearly overestimated PM2.5NO3−concentration, which was attributed to overestimation of production of ammonium nitrate (NH4NO3). This study conducted sensitivity analyses of factors associated with the model performance for PM2.5NO3−concentration, including temperature and relative humidity, emission of nitrogen oxides, seasonal variation of NH3emission, HNO3and NH3dry deposition velocities, and heterogeneous reaction probability of dinitrogen pentoxide. Change in NH3emission directly affected NH3concentration, and substantially affected NH4NO3concentration. Higher dry deposition velocities of HNO3and NH3led to substantial reductions of concentrations of the gaseous species and NH4NO3. Because uncertainties in NH3emission and dry deposition processes are probably large, these processes may be key factors for improvement of the model performance for PM2.5NO3−.Implications: The Community Multiscale Air Quality modeling system clearly overestimated the concentration of fine particulate nitrate in the Greater Tokyo Area of Japan, which was attributed to overestimation of production of ammonium nitrate. Sensitivity analyses were conducted for factors associated with the model performance for nitrate. Ammonia emission and dry deposition of nitric acid and ammonia may be key factors for improvement of the model performance.

Continuous monitoring of hourly PM2.5component concentrations has been performed in Japan. The objective of this study was to evaluate the advantages of continuous monitoring to obtain data that can be useful for regional air quality simulations. Inclusion of transboundary transport in the simulations improved the correlation between the observed and simulated hourly concentrations of SO42-, SO3-, secondary organic aerosols (SOA), and metals in PM2.5. Black carbon was an exception, suggesting the overestimation of emissions in upwind countries. Including volcanic and dust emissions also improved the correlations between the observed and simulated hourly concentrations of SO42-and metals, respectively. However, despite the good correlation achieved by including transboundary transport, it also resulted in overestimated NO32-and SOA concentrations in western Japan during the winter. Further improvements are necessary, such as balancing with SO42-and the dry deposition of gaseous HNO3for NO3-, and new treatment of the partitioning and aging of semivolatile organic aerosols, which have been incorporated into recent models for SOA. The differences in model performance with regard to simulating metal concentrations suggest imbalances in the speciation profiles used for countries other than Japan. Further, comparing the observed and simulated hourly concentrations helped identify the key processes driving air quality. This revealed evening peaks in black carbon concentrations, owing to the relatively stable atmosphere; and early morning peaks in NO3-concentration, owing to the low temperature and high humidity through thermodynamic equilibrium. This study demonstrated that continuous monitoring of hourly variations in PM2.5composition is valuable for understanding the roles of the emission sources and for improving future models, both of which contribute to deriving effective PM2.5suppression strategies.