Abstract. The results of regular observations of atmospheric CO₂ mixing ratios and its carbon isotope composition (δ¹³C, Δ¹⁴C), carried out at two continental sites located in central Europe are presented and discussed. The sites (Kasprowy Wierch, 49°14' N, 19°59' E, 1989 m a.s.l.; Krakow, 50°04' N, 19°55' E, 220 m a.s.l.), are located in two contrasting environments: (i) high-altitude mountaneous area, relatively free of anthropogenic influences, and (ii) typical urban environment with numerous local sources of carbon dioxide. Despite of relative proximity of those sites (ca. 100 km), substantial differences in both the recorded CO₂ levels and their isotopic composition were detected. The CO₂ mixing ratios measured in the urban atmosphere revealed quasi-permanent excess concentration of this gas when compared with near-by background atmosphere. The annual mean CO₂ concentration recorded in Krakow in 2004 was almost 10% higher than that recorded at high-altitude mountain site (Kasprowy Wierch). Such effect is occuring probably in all urban centers. Carbon isotopic composition of atmospheric CO₂ proved to be efficient tool for identification the surface CO₂ fluxes into the atmosphere related to fossil fuel burning and their influence on the recorded levels of this gas in the local atmosphere. The available records of Δ¹⁴C for Krakow and Kasprowy Wierch suggest gradual reduction of ¹⁴C-free CO₂ fluxes into the urban atmosphere of Krakow in the past several years.