Air pollution gases, such as ozone, cause various damages to plants, such as visible damage to the leaves and growth inhibition. To elucidate the mechanism of this damage is to understand the environmental stress response mechanism of plants, and to elucidate the plant’s defense mechanism against damage, as well as provide important knowledge for imparting stress tolerance to plants. Reactive oxygen species is one of the causative substances of plant damage caused by ozone, etc., but the mechanism from its generation to the manifestation of damage is very complicated. It has been shown that signal transmission is important. In addition, the importance of stomata opening and closing regulation, which is the absorption route of ozone to the leaves, has also been determined. I now describe the development of air pollution gas-tolerant plants by genetic manipulation of the reactive oxygen scavenging enzymes, which I have been working on since the late 1980s, the elucidation of the role of plant hormones in plant air pollution gas tolerance, and I review the overall understanding of the environmental stress response mechanism of plants by molecular genetic studies using mutants, and introduce the methods used to elucidate the mechanism and the findings obtained as a result.

Excess deposition of air pollutants derived from anthropogenic activities may disturb the material cycles and biological responses in forest ecosystems. The forest canopy is an important interface between the atmosphere and ecosystems, and epicuticular wax on a leaf surface quantitatively and chemically changes due to the atmospheric environment. Erosion and degradation of the wax and malfunction of the stomata due to particulate matter (PM) deposited on the leaf surface may accelerate tree water deficiency. The chemical properties of the wax are also related to a deposition process of the PM, such as elemental carbon, and PM-capturing/keeping mechanisms on the tree leaf surface should be investigated to efficiently utilize its air purification ability. Moreover, NO₃⁻ and NH₄⁺ absorptions and NH₃ emission on the leaf surface should also be investigated. In field studies of forested catchments with different climatic zones in the East Asian region, a sulfur isotopic analysis suggested that ecosystem responses are slow and recovery due to air pollution improvement requires time, even though SO₂ emissions and sulfur deposition are tending to decrease. The Asian climate seasonality largely controls the deposition processes of air pollutants and their dynamics in ecosystems. It is suggested that meteorological variations could play an important role, such as mobilization of the air-pollution legacy, especially in the recovery processes.

The field observation study of atmospheric deposition chemistry since 1985 was awarded the Academic Prize by the Japan Society of Atmospheric Environment in 2022. This review paper focuses on the following subjects; precipitation chemistry survey from regional or transboundary scales, development of dry deposition velocity calculation program, improvement of dry deposition components measuring method, and estimation of reactive nitrogen deposition. Furthermore, I would like to describe the advantages of regional-based research of the atmospheric environment from the viewpoint of its peculiarity and originality.

Tropospheric ozone has been the focus of attention as an air pollutant of concern for its effects on health and vegetation and also a short-lived climate forcer (SLCF) along with methane and black carbon (BC). Since ozone is secondarily produced through tropospheric photochemistry, a sophisticated chemical model covering the HO_x cycle reaction mechanism is necessary for impact assessment and future predictions. The HO_x cycle includes two processes that are considered to be potential sources of error. One is the heterogeneous uptake process of peroxy radicals (HO₂ and RO₂) onto clouds and aerosols, and the other is the reaction of OH radicals with unidentified and/or difficult-to-measure reactive species. In both cases, the evaluation of ozone production can change by several tens of percent with or without consideration, and their incorporation into atmospheric chemistry models remains a challenge. The author has quantitatively verified the suppression of ozone formation by aerosols by determining the uptake coefficient of peroxy radicals using a laser spectroscopy-based HO_x reactivity measurement system, and also investigated the sources of unidentified and difficult-to-measure OH reactive species through atmospheric observations and laboratory experiments. This paper reviews the results of previous research studies of both processes and current understanding.

Although it has been suggested that the organic peroxy radical (RO₂) uptake by ambient aerosols suppresses the ozone formation in the troposphere, atmospheric chemical model simulations often use a presumed uptake coefficient due to the lack of experimental values and the estimated suppression effect has remained unverified. In this study, we developed a method combining laser photolysis radical generation and laser induced fluorescence radical detection techniques (LP-LIF), and tested its performance to determine the uptake coefficient of RO₂ onto particles. We succeeded in determining the uptake coefficients of ISOPOO, RO₂ derived from the OH oxidation of isoprene onto standard NaCl particles to be 0.11±0.02. The dependence of the uptake coefficients on the particle surface and on the co-ion addition qualitatively corresponded to the model prediction, which validated the present method. Additionally, we connected a versatile aerosol concentration enrichment system (VACES) to LP-LIF and determined ISOPOO the uptake coefficient onto ambient aerosols to be 0.08±0.05 as an inverse-variance-weighted mean. Assuming all the RO₂ have the same uptake coefficient to ISOPOO, a 2–9% suppression of the ozone formation rate by RO₂ uptake was predicted under the clean sub-urban condition ([NOx] ~4 ppb, PM_2.5 ~5 µg m⁻³). For a more accurate evaluation, improvement of the measurement precision and further investigation with other RO₂ in the laboratory and atmospheric observations are required.