Abstract
To evaluate photochemical oxidants in detail, the total peroxy acyl nitrates (PANs) analyzer based on the TD/CAPS technique (cavity attenuated phase shift spectroscopy combined with a thermal dissociation reactor) was utilized and continuous observations of PANs, O3, NO2 and NO were successfully conducted over three years in a suburban site in Tokorozawa, Saitama, Japan. In this study, the period from April 2023 to August 2024 was investigated in order to characterize the relationship between the PANs and total oxidants (PO=O3+NO2) over one year and to focus on the outstanding cases in the summer of 2024. As the result of a correlation analysis between daytime PANs and PO, it was indicated that high PO events could be seen under the following conditions: (1) sunny days, (2) high temperature, (3) low NOx/NMHCs ratio (NOx-limited regime for O3), (4) sufficiently high PO intercepts and/or slopes for day-by-day regression lines between the PANs and PO, and (5) long lifetime of PAN due to high NO2/NO ratios. Consequently, during the over-3-year continuous observations, the practical utility of the PANs analyzer was confirmed. It was also confirmed that the correlation between total PANs and PO could be promising for evaluating and capturing the situations of photochemical ozone, including outstanding ozone events.
