# Urban CO2 Budget: Spatial and Seasonal Variability of CO2 Emissions in Krakow, Poland
## 2 Methods  
### Study Site  
Krakow is located in the southern part of the region called Lesser Poland, in a temperate climate of central Europe. The daily mean temperature is equal to 8.2 \({}^{\circ}\)C, with a variation between a minimum of -5.3 \({}^{\circ}\)C in January and a maximum of 24.6 \({}^{\circ}\)C in July. Precipitation occurs throughout the year with yearly mean amount of 678 mm, with the driest season being winter, with around 30 mm of precipitation per month; the most rain occurs from May to August, with around 80 mm per month on average (calculated for the period 1981-2010; Figure 1). During the study, the monthly mean temperature remained close to the values expected from the city climatology, while warm season precipitation varied significantly over subsequent years (Figure 1). The city is located in Vistula river valley surrounded by hills. This is the reason of significant wind speed reduction and frequent air temperature inversions. Such conditions stimulate accumulation of CO\({}_{2}\) within boundary layer, and result in a high amplitude of the diurnal CO\({}_{2}\) concentration cycle (up to 100 ppm), observed especially during winter season [16]. Krakow represents a typical urban environment, with a number of anthropogenic and natural CO\({}_{2}\) sources and sinks, like low emission sources, industry, transport, water reservoirs and city biosphere, including citizens and pets. The Vistula flows through Krakow latitudinally. The watercourse length of the Vistula within administrative borders of Krakow is 34 km, compared to the city span of about 26 km. The river is regulated within the city limits, including three navigation dams. Before entering Krakow, the Vistula drains densely populated areas, where agriculture and heavy industry is located. More detailed description of the Vistula river in Krakow reach is available in [17]. In order to measure CO\({}_{2}\) flux from soil, four sites with different type of land cover have been selected across the city (Figure 2). Site S1 was located on a lawn separating two lines of one of the main city traffic arteries. Due to increased emissions from traffic, the local biosphere is exposed to elevated CO\({}_{2}\) levels, even 20-40 ppm higher than at other locations in the city. Site S2 was located on the outskirts of a large urban meadow of 48 hectares, which is also a recreational area, and borders low and moderate traffic routes. According to historical records this area has never undergone drastic changes nor an urbanization processes, so the soil at this site has remained undisturbed for at least two hundred years. The measurement sites S1 and S2 have been described in detail in [18]. Site S3 was set up in a park adjacent to the meadow where the S2 site was located. The park was created in the nineteenth century and, since then, has been repeatedly transformed. The measurement site was located on one of the lawns in the least transformed portion of the park, in the vicinity of elm and oak  
Figure 1: Monthly mean air temperature and precipitation in Krakow (WMO station index: 12566) during the period of the study (2009–2014). The 30-year averages of air temperature and precipitation (1981–2010) are also shown. Horizontal axis depicts first letters of subsequent months; solid lines in the upper part of the figure depict mean monthly temperature, with an area between daily mean minimum and maximum temperatures shaded; bars and diamond markers indicate monthly precipitation. Each year of the study period is presented separately in different shades of blue, and the mean value for the study period is marked in red. Data source: Institute of Meteorology and Water Management. trees. A reference site, S4, was located on a suburban backyard lawn, outside the city administrative boundaries, and far away from busy traffic routes. Soil carbon content at each site has been analyzed with a CNS LECO 2000 elemental analyzer and pH was determined with the potentiometric method.