Abstract
The photochemical oxidant (Ox) concentrations observed at the monitoring site located in Aso somma (930 m) in the area of central Kyushu from April 2011 to May 2012 were used for evaluating the contributions of transportation from the continent, intrusion of the stratospheric ozone, and local photochemical Ox production. As the averaged diurnal change in the Ox concentrations was low, the Ox observed during the nighttime was regarded as the background Ox. In the spring, since the daytime Ox concentration data from multiple sites (including Aso somma and ground-based monitoring sites) showed almost the same level, as the averaged behavior in this season, the authors considered that the Ox level of the ground-based monitoring sites depended on vertical mixing of the background Ox in the upper layer. Based on the averaged diurnal change in the Ox concentration at the site in Aso somma, contributions of the averaged local photochemical Ox production to the daytime maximum value of Ox were estimated to be less than 10 % except in the summer season. On the other hand, based on evaluating the contributions for each day when high Ox concentration were observed, some cases showed the possibility that the contributions of the local photochemical Ox production were over 20 ppb. As the result of a multiple correlation analysis for the daily averaged Ox concentrations in the spring using the specific humidity and sulfate as variables, the authors considered that the background Ox in this season consisted of adding transportation from the continent to the base Ox concentration from intrusion of the stratospheric ozone.
