HO_x radicals play a key role in tropospheric ozone (O₃) formation, and understanding their behavior is essential for controlling the O₃ levels. While observation studies in urban areas have progressed, knowledge remains limited in suburban areas where anthropogenic and natural sources are mixed. This study used data from AQUAS-Kyoto 2018 and CMAQ modeling to evaluate the air quality in suburban areas. In the first half of the observation period, clean air was dominant, and OH reactivity was largely driven by biogenic emissions. On the other hand, in the latter half, air from urban areas increased the OH reactivity, likely due to transported anthropogenic compounds. CMAQ modeling generally reproduced the BVOCs and O₃ concentrations throughout the observation period, but tended to underestimate anthropogenic substances, and in the analysis of the O₃ production regime, the model showed an opposite tendency, with the VOC regime in the first half and the NO_x regime in the second half being stronger than the observed results. These results indicated that the air quality is complex in suburban areas, which are influenced by various sources, and that differences in the O₃ precursor concentrations and sensitivity analysis results are likely to occur, providing insight for improving the air quality and chemical transport model accuracy.

The applicability of the one-week continuous sampling method and the passive sampling method for measuring ethylene oxide and propylene oxide in ambient air was evaluated using derivatized solid-phase collection and gas chromatography-mass spectrometry. The goal was to develop a method that could more accurately calculate the annual average concentrations and conduct simplified, multi-site monitoring. A comparative test using a sampling pump showed no difference between the one-week continuous sampling method and the 24-hour sampling method (7 consecutive samples of a 24-hour collection), thus the current monitoring method for hazardous air pollutants could be applied to the one-week continuous sampling. In addition, evaluating the applicability of a commercially-available passive sampler for ambient air measurements showed that the sensitivity of the measurements was insufficient. To improve sensitivity, a new sampler with a refined design was created and evaluated, that achieved a sufficient sensitivity for ambient air measurements. The refined passive sampler’s sampling rate was calculated to be 0.00291 m³/h for ethylene oxide and 0.00248 m³/h for propylene oxide. This is more than twice the rate set by the manufacturer for the commercially-available passive sampler.