## 3 Results
### Biogenic CO\({}_{2}\) Fluxes and Anthropogenic CO\({}_{2}\) Emissions in the Greater Tokyo Area
The nighttime vegetated land of the Greater Tokyo Area was a natural carbon source, collectively emitting 0.08 \(\pm\) 0.01 \(\times\) 10\({}^{4}\) to 0.09 \(\pm\) 0.01 \(\times\) 10\({}^{4}\) ton CO\({}_{2}\) h\({}^{-1}\) in January and 0.56 \(\pm\) 0.09 \(\times\) 10\({}^{4}\) to 0.60 \(\pm\) 0.10 \(\times\) 10\({}^{4}\) ton CO\({}_{2}\) h\({}^{-1}\) in July, which were 3.07 \(\pm\) 0.51% to 2.34 \(\pm\) 0.41% and 21.97 \(\pm\) 3.38% to 17.80 \(\pm\) 2.97% of the hourly integrated anthropogenic CO\({}_{2}\) emissions for January and July, respectively. Depending on whether the photosynthetic CO\({}_{2}\) uptake would completely compensate for the biogenic CO\({}_{2}\) emission in each grid cell or not, the daytime net biogenic CO\({}_{2}\) flux from ecosystems to the atmosphere was either negative or positive. Here, negative net biogenic CO\({}_{2}\) flux values mean that the direction of carbon flow is reversed (from atmosphere to the ecosystem): a natural carbon sink. The maximal negative hourly integrated net biogenic CO\({}_{2}\) flux of the Greater Tokyo Area often occurred around 12 a.m. to 2 p.m. in all seasons, \(-\)0.46 \(\pm\) 0.14 \(\times\) 10\({}^{4}\) ton CO\({}_{2}\) h\({}^{-1}\) in January in winter to \(-\)2.26 \(\pm\) 0.42 \(\times\) 10\({}^{4}\) ton CO\({}_{2}\) h\({}^{-1}\) in July in summer, would potentially offset 10.52 \(\pm\) 3.17% to 55.42 \(\pm\) 10.39% of the hourly anthropogenic emissions. Overall, the sub-daily patterns of hourly integrated biogenic CO\({}_{2}\) emissions, photosynthetic CO\({}_{2}\) uptake, and net biogenic CO\({}_{2}\) flux of the Greater Tokyo Area were bell-shaped, whereas the ranges of hourly integrated values increased from winter to spring and from spring to summer, subsequently dropping in autumn. The intraday peaks almost always occurred around midday, but the highest hourly integrated biogenic CO\({}_{2}\) emissions often appeared several hours later than the photosynthetic CO\({}_{2}\) uptake. In each month, the variation of hourly integrated photosynthetic CO\({}_{2}\) uptake of the Greater Tokyo Area was much greater than that of biogenic CO\({}_{2}\) emissions. As a result, the integrated net biogenic CO\({}_{2}\) flux fluctuated between positive and negative figures within a day. Figure 11 presents the integrated anthropogenic CO\({}_{2}\) emissions, biogenic CO\({}_{2}\) emissions, photosynthetic CO\({}_{2}\) uptake, and net biogenic CO\({}_{2}\) flux of the Greater Tokyo Area at the monthly scale. In winter to early spring (December to March), the integrated biogenic CO\({}_{2}\) flux was lower than the anthropogenic one by more than one order of magnitude (the ratio of integrated biogenic CO\({}_{2}\) flux to anthropogenic emission was only 3.34 \(\pm\) 0.54% in February). From April to November, both photosynthesis and biogenic respiration became more active, up to 34.29 \(\pm\) 5.92% and 20.46 \(\pm\) 1.96% of the integrated anthropogenic CO\({}_{2}\) emissions. Consequently, the integrated biogenic CO\({}_{2}\) flux was up to 17.06 \(\pm\) 5.44% of the anthropogenic one in June.