Measurements of atmospheric CO
2 were made continuously at a height of 34 m in Sapporo (lat 43.1°N, long 141.3°E), located in northern Japan, from November 2004 to December 2005. Air samples for measurements of atmospheric CO, CH
4, and CO
2 were also taken in Sapporo and Ishikari Hama (lat 43.3°N, long 141.4°E), facing the Japan Sea, at 10- to 14-day intervals during the same period. In Sapporo, the atmospheric CO
2 data showed clear diurnal and seasonal variations. During the diurnal variation, the maximum CO
2 concentration occurred in the morning and the broad minimum in the daytime. The daily mean value of atmospheric CO
2 in the daytime (11-16 JST) was at a maximum in winter to spring and a minimum in summer. From December to February, the daytime atmospheric CO
2 concentration was about 8-13 ppm higher than that in the background air at Ishikari Hama; from July to August, it was nearly equal to that of the background air. In winter, the atmospheric CO concentrations in Ishikari Hama and Sapporo showed a good correlation with atmospheric CO
2 (10 ppb CO/ppm CO
2,
r = 0.82). However, atmospheric CH
4 remained fairly constant against CO
2 change. In summer, CO
2 flux by the photosynthesis of terrestrial vegetation between 11 and 16 JST was nearly equal to that of area-averaged CO
2 emission (between Ishikari Hama and Sapporo) due to human activities, which was estimated to be 11 μmol m
-2s
-1 in the catchment area.
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