## 3 Results
### Biogenic CO\({}_{2}\) Fluxes and Anthropogenic CO\({}_{2}\) Emissions in the Greater Tokyo Area
Figure 9: Diurnal variation of (**a**–**l**) hourly estimated anthropogenic CO\({}_{2}\) emission (gC m\({}^{-2}\) h\({}^{-1}\)) in the study area in July 2018. The spatial distribution of emission was based on EAGrid2000 Japan, adjusted by the annual emissions in 2018 published by the Ministry of the Environment of Japan. As meteorological conditions became more favorable for _SOC_ decomposition from winter to summer and vegetation became more active in terms of both maintenance and growing activities, hourly integrated biogenic CO2 emissions of the Greater Tokyo Area increased considerably. In July, the lowest hourly integrated biogenic CO2 emissions were at 5 a.m. and was estimated to be 0.56 \(\pm\) 0.08 \(\times\) 10\({}^{4}\) ton CO2 h\({}^{-1}\), roughly 18.76 \(\pm\) 2.80% of the hourly integrated anthropogenic CO2 emissions in the Greater Tokyo Area and 6.35 times the biogenic value in January. The strongest hourly integrated biogenic CO2 emissions were found at noon and were estimated to be 0.96 \(\pm\) 0.13 \(\times\) 10\({}^{4}\) ton CO2 h\({}^{-1}\), which was 6.39 times that of January's biogenic level, and 23.62 \(\pm\) 3.13% of the hourly integrated anthropogenic CO2 emissions, as the latter also increased after several hour. Thirdly, hourly integrated photosynthetic CO2 uptake of the Greater Tokyo Area represents the amount of absorbed carbon by forests, grassland or urban vegetation, varying both diurnally and seasonally. Because the calculation of _GPP_ in our model was under the assumption that the supply of CO2 for photosynthetic reactions in C3 plants is controlled by stomata in daytime only, the hourly integrated photosynthetic CO2 uptake at night was 0. In winter, the absolute value of hourly integrated photosynthetic CO2 uptake in both the early morning and late afternoon was low and was the lowest (0.04 \(\pm\) 0.06 \(\times\) 10\({}^{4}\) ton CO2 h\({}^{-1}\) and 1.34 \(\pm\) 2.03% of the hourly integrated anthropogenic CO2 emissions in the Greater Tokyo Area) at 5 a.m. in January. Because photosynthetic enzymes became more active at higher winter temperatures and because more photosynthetically active radiation was available around midday, the hourly integrated photosynthetic CO2 uptake was en  
Figure 10: **(a-1)** Hourly integrated anthropogenic CO2 emissions (10\({}^{4}\) ton CO2 h\({}^{-1}\)) in 2018, compared to hourly integrated biogenic CO2 emissions, photosynthetic CO2 uptake, and net biogenic CO2 flux of the Greater Tokyo Area (10\({}^{4}\) ton CO2 h\({}^{-1}\)) during the period 2010–2018. Shadows represent the variation (the minimum to the maximum) of hourly integrated biogenic CO2 emission (red), photosynthetic CO2 uptake (green), and net biogenic CO2 flux (blue). hanced. For January, the highest absolute value was obtained around 2 p.m., and that value (0.62 \(\pm\) 0.17 \(\times\) 10\({}^{4}\) ton CO\({}_{2}\) h\({}^{-1}\)) was 14.08 \(\pm\) 3.89% of the hourly integrated anthropogenic CO\({}_{2}\) emissions. As the seasons changed, hourly integrated photosynthetic CO\({}_{2}\) uptake of the Greater Tokyo Area reached the highest level in July, with an absolute value of 3.22 \(\pm\) 0.50 \(\times\) 10\({}^{4}\) ton CO\({}_{2}\) h\({}^{-1}\) at noon and 5.42 times the January value. This amount was 79.04 \(\pm\) 12.31% of the hourly integrated anthropogenic CO\({}_{2}\) emissions. Finally, the hourly integrated net biogenic CO\({}_{2}\) flux of the Greater Tokyo Area represents the amount of CO\({}_{2}\) flow from ecosystems to the atmosphere. At night, such flow was one-way, from forests, grasslands, and urban vegetated areas into the air.