The summer of 2018 was the longest and hottest ever. The highest temperature in the history of domestic meteorological observation, 41.1°C, was observed at the Kumagaya Meteorological Station, Saitama Prefecture.
Generally, photochemical air pollution and secondary aerosol formation occur easily in summer. In order to characterize air pollutants, such as photochemical oxidant (mainly ozone, O3) and fine particles less than 2.5 micrometers in diameter (PM2.5), in the 2018 summer, trends of meteorological data and changes in air pollutant concentrations from 2009 to 2018 were obtained from the Automated Meteorological Data Acquisition System (AMeDAS) and the air pollution monitoring station, respectively; relationships between them were investigated with focus on Saitama Prefecture, where the levels of both temperature and O3 concentration were highest in the Kanto region.
The highest temperatures in the northern area were higher than those in the southern area of Saitama Prefecture, while O3 levels exhibited the opposite pattern. In addition, the obvious weekend effect was found in the recent three years.
Daily PM2.5 concentrations in July and August were lower than the air quality standard (i.e., 35 μg/m3). No regional differences were observed within Saitama Prefecture. On all the days when the highest O3 concentration was ≥100 ppb or the highest PM2.5 concentration was ≥25 μg/m3, the highest temperature was greater than 35°C. The lowest values among the maximum daily O3 and PM2.5 concentrations increased with increase in the highest temperature beyond 35°C.