# Urban CO2 Budget: Spatial and Seasonal Variability of CO2 Emissions in Krakow, Poland
## 4 Conclusions  
The CO\({}_{2}\) flux from soils in Krakow is an important component of the city's carbon budget. It is characterized by strong seasonal variability, with maximum values occurring in early summer and minimum during winter. The soil CO\({}_{2}\) flux depends primarily on temperature [11] and humidity [12], but also on the soil type: at the site representing undisturbed natural soil, the highest values of soil CO\({}_{2}\) flux were measured. Small but positive soil CO\({}_{2}\) fluxes measured in winter confirm that soil respiration is active also during this season, despite of temperatures approaching 0 \({}^{\circ}\)C or being negative.  
Emissions of CO\({}_{2}\) from water courses reflect mainly the flow regime of water. Water damming has large effect on the observed emissions. The relatively small area covered by water courses within Krakow administrative borders means that the contribution of water sources to the total CO\({}_{2}\) budget of the city is minor, accounting for only 0.1% of the total CO\({}_{2}\) emissions annually (Table 4). However, with the flux density comparable to soil emissions, it should not be neglected in urban CO\({}_{2}\) budgets, especially in cities with larger water bodies.  
Krakow is a net source of CO\({}_{2}\), with approximately 7.3 \(\pm\) 0.8 Mt CO\({}_{2}\) being emitted annually from the administrative area of the city. Although, under favorable conditions, the local vegetation can assimilate enough CO\({}_{2}\) to generate negative net CO\({}_{2}\) fluxes to the local atmosphere during summer, on the annual time-scale, it is a source of CO\({}_{2}\), being responsible for 9% of the total emissions. Fossil fuel combustion is responsible for 88% of the total CO\({}_{2}\) emissions in the city while the respiration of inhabitants accounts for ca. 3%. Although the CO\({}_{2}\) budget of an urban area with a relatively high green fraction can be negative [45], for cities with strong industrial sources of CO\({}_{2}\), achieving carbon-neutrality can be very difficult.  
Conceptualization, A.J.-K., M.Z., and K.R.; methodology, A.J.-K., M.Z., and P.W.; investigation, A.J.-K., M.Z., and P.W.; writing--original draft preparation, A.J.-K.; writing--review and editing, M.Z., K.R., and P.W. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This work was partially supported by the Ministry of Science and Higher Education, project No. 817/N-COST/2010/0, and project No. 16.16.220.842 B02; and European Science Foundation TTorch exchange grant No. 4705.  
**Acknowledgments:** Authors would like to express gratitude towards [PERSON] and [PERSON] from Institute for Atmospheric and Earth System Research, University of Helsinki, for essential support in REA data handling, and [PERSON] from Meteorology Department, Poznan University of Life Sciences, for helping with system design and construction. We would also like to appreciate our colleagues from AGH University of Science and Technology for tremendous help with field measurement campaigns.  
**Conflicts of Interest:** The authors declare no conflict of interest.