Diurnal and seasonal variations in atmospheric CO2 in Sapporo, Japan: Anthropogenic sources and biogenic sinks

Abstract

Measurements of atmospheric CO2 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, CH4, and CO2 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 CO2 data showed clear diurnal and seasonal variations. During the diurnal variation, the maximum CO2 concentration occurred in the morning and the broad minimum in the daytime. The daily mean value of atmospheric CO2 in the daytime (11-16 IST) was at a maximum in winter to spring and a minimum in summer. From December to February, the daytime atmospheric CO2 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 CO2 (10 ppb CO/PPM CO2, r = 0. 82). However, atmospheric CH4 remained fairly constant against CO2 change. In summer, CO2 flux by the photosynthesis of terrestrial vegetation between 11 and 16 JST was nearly equal to that of area-averaged CO2 emission (between Ishikari Hama and Sapporo) due to human activities, which was estimated to be 11 μmol m-2s-1 in the catchment area. Copyright © 2007 by The Geochemical Society of Japan.