Assessing surface fluxes of CO2 and CH4 in urban environment: a reconnaissance study in Krakow, Southern Poland

Regular observations of atmospheric mixing ratios of CO₂ and CH₄, combined with sodar measurements of the mixing layer height in the lower troposphere were used to assess night-time surface fluxes of these gases in the urban environment (Krakow, southern Poland). The measurements performed over the 4-yr period (May 2005–May 2009) revealed a distinct seasonality of surface night-time fluxes of CO₂, with the minimum of ca. 2 mmol m^-2 h^-1 during winter months and the maximum of ca. 20 mmol m^-2 h^-1 observed during summer months. The observed seasonality was induced by the biospheric component (soil respiration) which dominates the measured surface CO₂ fluxes during summer months. The surface fluxes of CH₄ scatter between ca. 50 and 200 ¼mol m.2 h.1, without clear seasonal trend. Significant flux of CH₄ into the atmosphere (mean value over the whole observation period equal to ca. 97 ¼mol m^-2 h^-1), indicates a presence of relatively strong methane source on the investigated area. This source is linked to methane leakages from the city gas distribution network.