Abstract
The concentration of NO2 in the air above the earth's surface was observed at the western suburb of Tokyo for the period from September 1960 to August 1961, using an automatic gas sampler.
The results of determination revealed that NO2 concentration showed a marked diurnal variation in winter with two maxima respectively at about 3 hours after sunrise and at about 2 hours after sunset, and two minima respectively at sunrise and in the afternoon. The time of occurrence of the afternoon minimum varied greatly day to day, while those of the dawn minimum and of the evening maximum did not change greatly, falling on most of days within the range of plus and minus one hour from the monthly average. The morning peak was always lower than that in the evening and no morning maximum was observed often in summer as well as on windy days in other seasons. The monthly mean concentration of NO2 at night was higher than that at day and the maximum values of 78 and 54μgNO2/m3 were observed in December respectively. The diurnal variation in NO2 seems to be attributable to the combination of meteorological conditions and photochemical effect.
