# Urban CO2 Budget: Spatial and Seasonal Variability of CO2 Emissions in Krakow, Poland
## 3 Results and Discussion
### CO\({}_{2}\) Budget for Krakow Agglomeration  
According to the municipal land-use data green areas cover more than a half of the total administrative city area (Table 4; [36]). The total soil emissions of CO\({}_{2}\) from green areas located within the city limits are equal 1.378 \(\mathrm{M}\mathrm{C}\mathrm{O}_{2}\) yr\({}^{-1}\). Along with CO\({}_{2}\) emissions from water courses in Krakow, they account for 1.389 \(\mathrm{M}\mathrm{C}\mathrm{O}_{2}\) that is emitted annually to the local atmosphere (Table 4). The above estimate was obtained based on direct measurements of surface CO\({}_{2}\) fluxes. Therefore, it does not take into account above-ground plant emissions, as well as the CO\({}_{2}\) photosynthetic uptake. The assessment of local-scale CO\({}_{2}\) budget within the REA-AGH source area resulted in photosynthetic uptake flux of 3.27 \(\mathrm{\SIUnitSymbolMicro m}^{-2}\) s\({}^{-1}\). Green areas occupy 53% of the surface within the administrative borders of the city, corresponding to area of 174 \(\mathrm{km}^{2}\) (Table 4) therefore, in total, the city biosphere absorbs approximately 0.79 \(\mathrm{M}\mathrm{t}\mathrm{C}\mathrm{O}_{2}\) annually. As for other cities where the carbon budget was estimated, Krakow has been found to be a net source of CO\({}_{2}\). The CO\({}_{2}\) budget entire administrative area of the city is presented below (cf. Equation (3)):  
\[ \begin{array}{l}\mathrm{F}_{\mathrm{tot}}=\mathrm{C}_{\mathrm{tra}}+\mathrm{ C}_{\mathrm{res}}+\mathrm{C}_{\mathrm{ind}}+\mathrm{R}_{\mathrm{soil}}+\mathrm{R}_{\mathrm{riv}}+ \mathrm{R}_{\mathrm{hum}}-\mathrm{G}\mathrm{P}\mathrm{P}_{\mathrm{U}}\\ =0.37+1.10+4.97+1.378+0.011+0.23-0.79=7.27\ \mathrm{M}\mathrm{t}\mathrm{C} \mathrm{O}_{2}\mathrm{yr}^{-1}.\end{array}  \tag{5}\]  
Several components of the net CO\({}_{2}\) flux vary seasonally, so some variation of F\({}_{\mathrm{tot}}\) should be expected. Soil CO\({}_{2}\) emissions strongly depend on the season, with temperature being the main driver: CO\({}_{2}\) flux measured in different seasons at the same location could differ by more than one order of magnitude, with the maximum values observed in spring and summer and the minimum in winter. CO\({}_{2}\) uptake from the local atmosphere vary seasonally as well, with the maximum occurring during spring and summer. On an annual scale, the vegetation in Krakow assimilates more than a half of biogenic CO\({}_{2}\) (Equation (5)). In a temperate climate, the seasonal variability of energy and heat demand is pronounced as well, with both coal and natural gas consumption amplitude reaching 60% of annual average [5]. Relatively low emissions from fossil fuel burning, combined with maximum of photosynthetic uptake of CO\({}_{2}\) in the warm season, result in a distinct minimum of the net CO\({}_{2}\) emissions from the city. This effect has previously been shown for the CO\({}_{2}\) concentration in the atmosphere of Krakow [3; 5; 44]. The Krakow municipal area produces around 7.3 \(\mathrm{M}\mathrm{t}\mathrm{C}\mathrm{O}_{2}\) annually, which corresponds to a flux density of 22.3 kg CO\({}_{2}\) m\({}^{-2}\) yr\({}^{-1}\), or 6.1 kg C m\({}^{-2}\) yr\({}^{-1}\). Similar results have been obtained for other European cities (Table 5). They are also in agreement with the prediction of a model based on satellite land cover data which estimates around 7 kg C m\({}^{-2}\) annually for Krakow [45]. Industry is the most important source of CO\({}_{2}\) in Krakow, accounting for 68% of the total annual emissions. Local biosphere net exchange accounts for 9% of the total emissions, with more than a half of the emitted CO\({}_{2}\) being assimilated by the vegetation trough photosynthetic uptake. Traffic and residential sources account for 5% and 15% of the total emission, respectively. Human respiration