Diurnal Variation of CO2 Flux in an Urban Area of Tokyo

From November 2012 to October 2013, we measured the eddy covariance flux of carbon dioxide (CO2) in the middle of Tokyo, Japan. The study area is characterized as having low-vegetated mid-rise residence with some arterial roads. Contribution of human activities to the measured CO2 flux was evaluated by hourly inventory analysis. The study area serves as a net source of CO2 whose annual total was +4300 gC m(-2) yr(-1). The resulting diurnal CO2 flux has one peak in the morning and one in late evening. This diurnal amplitude is larger in winter and also larger on weekday. An hourly inventory analysis for winter shows that the morning peak arises from both traffic and household gas use, whereas the evening peak arises from just the household gas. The significant difference in the morning flux between weekday and holiday should be attributed to the traffic emission.