# Urban CO2 Budget: Spatial and Seasonal Variability of CO2 Emissions in Krakow, Poland
## 3 Results and Discussion
### Urban CO\({}_{2}\) Budget on a Local Scale  
The local-scale CO\({}_{2}\) budget (Equation (4)) was used to calculate the photosynthetic uptake from the atmosphere in a source area of the REA-AGH site (GPP\({}_{\rm U}\)). In this equation, F\({}_{\rm net}\) denotes the total net CO\({}_{2}\) flux density measured by REA with the median of 5.71 umol m\({}^{-2}\) s\({}^{-1}\). Anthropogenic emissions in Krakow as of 2010, according to the EDGAR inventory [34], are listed in Table 3. The estimated annual CO\({}_{2}\) flux from transportation and built-up areas within the REA-AGH source area is equal to 1.37 umol m\({}^{-2}\) s\({}^{-1}\) and 4.72 umol m\({}^{-2}\) s\({}^{-1}\), respectively.  
According to the city records [21], at the time of the study 2357 inhabitants lived within the source area of the REA-AGH site. Hence, the input to the local CO\({}_{2}\) budget from human respiration is estimated as 1.1 umol m\({}^{-2}\) s\({}^{-1}\). Two of the soil flux measurement sites were located within a short distance from the source area: S1 and S3 (Figure 2). Utilizing the data collected at those two sites, the mean soil CO\({}_{2}\) flux density at the source area was calculated to 3.47 \(\pm\) 0.28 umol m\({}^{-2}\) s\({}^{-1}\). In the REA-AGH source area, the green surface fraction is 52%, so this number should be scaled-down to 1.8 umol m\({}^{-2}\) s\({}^{-1}\). The GPP\({}_{\rm U}\) calculated using Equation (4) and the estimated components is equal to 3.27 umol m\({}^{-2}\) s\({}^{-1}\).  
The calculation of the local photosynthetic uptake flux was performed with the assumption that local vegetation is the only source of CO\({}_{2}\) flux recorded from the green sector of REA-AGH site source area. This assumption is not entirely met--in the green sector, greenery is dominant but not the only land-use type. There are also traffic lanes and a few institutional buildings located there (Figure 3). Therefore, a part of the recorded CO\({}_{2}\) flux from this direction originates from sources other than vegetation. This may lead to underestimation of the calculated GPP\({}_{\rm U}\), as has been observed in previous studies of CO\({}_{2}\) net flux from highly heterogeneous areas [43].  
\begin{table}
\begin{tabular}{l c} \hline \hline
**Emission Category 1** & **CO\({}_{2}\) Emission [MtCO\({}_{2}\) yr\({}^{-1}\)]** \\ \hline Energy and industry & \\ (1A1a, 1A2, 2A, 2B, 2C1a, 2C1c, 2C1e, 2C1f, 2C2, 2G, 3) & 4.967 \\ Transportation (1A3a, 1A3b, 1A3c, 1A3d, 1A3e) & 0.369 \\ Commercial/residential buildings and waste (1A4, 1A5, 6C) & 1.102 \\ \hline \hline \end{tabular}
\end{table}
Table 3: CO\({}_{2}\) anthropogenic emissions inventory in Krakow as of 2010, according to 2019 edition of the Emission Database for Global Atmospheric Research (EDGAR) [34].  
Figure 6: Box-and-whisker plot of seasonal variability of net CO\({}_{2}\) flux density originating from different land-use sectors. Shown is median, 5–95% bars, and 25–75% boxes. Letters at the bottom of the figure denote seasons with first letters of the month (see text for details).