O 2 : CO 2 exchange ratio for net turbulent flux observed in an urban area of Tokyo, Japan, and its application to an evaluation of anthropogenic CO 2 emissions

Ishidoya, Shigeyuki; Sugawara, Hirofumi; Terao, Yukio; Kaneyasu, Naoki; Aoki, Nobuyuki; Tsuboi, Kazuhiro; Kondo, Hiroaki

In order to examine inline-formulaO2 consumption and inline-formulaCO2 emission in a megacity, continuous observations of atmospheric inline-formulaO2 and inline-formulaCO2 concentrations, along with inline-formulaCO2 flux, have been carried out simultaneously since March 2016 at the Yoyogi (YYG) site located in the middle of Tokyo, Japan. An average inline-formulaO2 : CO2 exchange ratio for net turbulent inline-formulaO2 and inline-formulaCO2 fluxes (ORinline-formulaF) between the urban area and the overlaying atmosphere was obtained based on an aerodynamic method using the observed inline-formulaO2 and inline-formulaCO2 concentrations. The yearly mean ORinline-formulaF was found to be 1.62, falling within the range of the average OR values of liquid and gas fuels, and the annual average daily mean inline-formulaO2 flux at YYG was estimated to be inline-formula−16.3inline-formulaµmol minline-formula−2 sinline-formula−1 based on the ORinline-formulaF and inline-formulaCO2 flux. By using the observed ORinline-formulaF and inline-formulaCO2 flux, along with the inventory-based inline-formulaCO2 emission from human respiration, we estimated the average diurnal cycles of inline-formulaCO2 fluxes from gas and liquid fuel consumption separately for each season. Both the estimated and inventory-based inline-formulaCO2 fluxes from gas fuel consumption showed average diurnal cycles with two peaks, one in the morning and another one in the evening; however, the evening peak of the inventory-based gas consumption was much larger than that estimated from the inline-formulaCO2 flux. This can explain the discrepancy between the observed and inventory-based total inline-formulaCO2 fluxes at YYG. Therefore, simultaneous observations of ORinline-formulaF and inline-formulaCO2 flux are useful in validating inline-formulaCO2 emission inventories from statistical data.

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Ishidoya, Shigeyuki / Sugawara, Hirofumi / Terao, Yukio / et al: O2 : CO2 exchange ratio for net turbulent flux observed in an urban area of Tokyo, Japan, and its application to an evaluation of anthropogenic CO2 emissions. 2020. Copernicus Publications.

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