In the early 1990s, acid rain (acidification) became a serious issue after the background ozone issue. A hybrid model was developed by combining trajectory and Eulerian models in order to predict and assess the long-range transport of sulfur compounds. The hybrid model performed well in predictions at sites influenced by nearby sources. By participating in the planning and implementation of phases I and II of the model intercomparison study, MICS-Asia, differences among the participating models and their causes became apparent. Continuous monitoring of gaseous and particulate matter began in Komae, Tokyo, in order to understand actual behavior. The observed seasonality of gas–aerosol partitioning of nitrate was well interpreted by a thermodynamic equilibrium model, which suggested that the particles were internally mixed. The MM5/CMAQ modeling system showed that emission reductions in Greater Tokyo were effective to some extent for the mitigation of secondary inorganic aerosol and that the sensitivity differed with the seasons and places. Analysis of aerosol composition in Jeju, Korea, by the thermodynamic equilibrium model indicated that fine-particulate ammonium nitrate would increase there with the NO_x and ammonia emissions in East Asia. In Fukue, episodes that nss-sulfate increased before the dust aerosol were observed, but one of them was influenced by the volcanic plumes from Mt. Miyake.

Field observation research of fine particulate matter and development of photocatalytic material for air clarification were given to an award by the Japan Society of Atmospheric Environment in 2019. This review paper focuses on this subject. My first research subject was PM_2.5 monitoring as a researcher in the research center established by the Saitama prefectural government. Some field research studies, such as parallel observation of PM₁ and PM_2.5, research of transboundary air pollution at the top of Mt. Fuji, international collaborative research between China, Korea and Japan, and magnetic properties of dust emitted from coal combustion in the agricultural areas of China, were carried out and the results were briefly introduced. The latter research, except for the development of photocatalystic materials, was not sufficiently explained. I would like to describe the development of atmospheric environment research linked to different research fields.

The tropospheric ozone concentrations have rapidly increased in the developing Asian countries. Elevated ozone concentrations reduce the yield of crops, including rice, which is the most important food crop in Asia. Previous studies have indicated that the current level of ozone is sufficiently high enough to reduce the grain yield of rice. However, the molecular mechanisms response to chronic ozone stress on the growth and the yield are poorly understood. The author and collaborators have carried out the experiments of chronic ozone exposure using several dozen domestic and foreign rice cultivars, the proteome analysis in leaves of rice cultivars, which show the different ozone sensitivities, and the genotypic analysis of quantitative trait loci. As a result, we found a novel mechanism of ozone-induced yield reduction in rice, especially indica cultivars, which is not caused by the reduction in photosynthetic activity as associated with visible leaf injury and leaf senescence. In this paper, the results of our studies on the molecular mechanism of ozone-induced reduction in grain yield and quality of rice are described.