At the summit of Mt. Fuji in July and August from 2012 to 2018, 27 kinds of anthropogenic volatile organic compounds (AVOCs) and 6 types of biogenic volatile organic compounds (BVOCs) in the air and in cloud water were determined. AVOCs occupied about 90% of the VOCs in the cloud water (volume-weighted mean VOCs concentration: 2.07 nM, n=159) and the main component was toluene, reflecting its high concentration in the ambient air. The concentration of the AVOCs in the cloud water was high when the airmass was transported from the southern continent and was about 1.5 times higher than that when it came from the ocean. The concentration of toluene in the cloud water decreased exponentially with the increase in the total ion concentration. The concentrations of some VOCs such as chloroform, o-xylene, and limonen in the cloud water were several times higher than their Henry’s law predicted values. Among the chlorinated hydrocarbons, highly hydrophobic chloroform was more concentrated than dichloromethane in the cloud water. Atmospheric surfactants such as HULIS (Humic-like Substances) could affect the enrichment of the VOCs in the cloud water even in the free troposphere.

The detailed daily variations of ions, organic components and organic molecular marker (levoglucosan) in fine particles (PM_2.5) were obtained by a round-year monitoring of filter sampling in the Tokyo Metropolitan area in 2014FY. In order to obtain Percent Modern Carbon (pMC), radiocarbon (¹⁴C) contained in total carbon (TC) and elemental carbon (EC) of 26 samples collected on the day of a high PM_2.5 concentration from 2013 to 2016 were measured. The pMC of the organic carbon (OC) was calculated from the obtained pMC of TC and EC. As a result, the concentration of levoglucosan in Tokyo was low in the summer and increased in the autumn and winter. The results of a wind direction analysis showed that the concentration of levoglucosan increased when the wind direction was from the agricultural area. It is suggested that the origin of the OC is strongly influenced by biomass burning from autumn to winter even in the central area where farmland is not located within a radius of 10 km. In order to estimate the origin of the OC in PM_2.5, the comparison of the ratio of the biomass burning origin estimated from the concentrations of levoglucosan and OC, and the pMC of the OC calculated from pMC of TC and EC measurement were conducted. The contribution of biomass burning in the OC estimated from the levoglucosan concentration was 13–31% in the autumn–winter and 2.6–6.2% in the summer, whereas, the pMC of the OC was 56 (spring), 61 (summer), and 64 (autumn–winter), which did not indicate a significant seasonal difference. These results indicate that modern carbon (biomass origin) is the major component of the OC in the urban area throughout the year. It was suggested that comparison with the pMC in the OC and the biomass burning OC estimated from levoglucosan, the sources of the biogenic carbon in the OC are that biomass burning in the autumn–winter and biomass sources other than biomass burning in the spring–summer.

Ozone is the one of the important oxidants in the atmospheric chemistry and also has adverse effects on plant and human health. The ozone concentration has an increasing trend in East Asia. There are a few monitoring sites which meets the air quality standard regarding ozone. In order to focus on the relation between high ozone concentration episodes and emission sources, temporal variation in the ozone concentration from 2005 to 2017 in five Japanese remote sites of Rishiri, Sadoseki, Oki, Tsushima, and Goto were analyzed. The high concentration outliers (O_{3 outlier}) were defined from normal data (O_{3 normal}) using the two curve fitting methods. The traceback analysis using a backward trajectory (METEX) was conducted to determine the relation between the transport area and the O_{3 outlier}. The frequency of transport from the Korean Peninsula to Rishiri was increased in O_{3 outlier}. The air mass was transported from South China or Korea to Oki in O_{3 outlier}. There is a deep relation between the Korean Peninsula and South China as the transport pathway. The difference in the transport pathway has a significant effect on the high ozone concentration in the remote area.

The mechanism of severe O₃ pollution in the Tokyo metropolitan area (TMA) was examined using observation data from ozone sonde monitoring and the Atmospheric Environment Regional Observation System during the period from July 23 to 24, 2018. Launch of the ozone sonde was conducted five times during this period at a field located in Hiratsuka City. In the ozone sonde monitoring launched at 14:00 on 24 July, the O₃ concentration became the highest in the range from the surface up to 2,000 m above ground level. According to the horizontal analysis for the O₃ concentration, it was suggested that the high O₃ concentration on 24 July was caused by supplying accumulated O₃ in the upper air into the mixing layer, and by a relatively higher background concentration on the land and the ocean that originated in the higher O₃ concentration which appeared during the night on 23 July. In addition, it was considered that the NO titration effect was involved in the vertical profile of the O₃ concentration at 14:00 on 24 July. It is expected that the ozone sonde data introduced here would contribute to understanding the mechanism of the severe O₃ pollutant in TMA and for the evaluation of the performance of the air quality model.