Abstract This paper describes results of chemical and isotopic analysis of inorganic carbon species in the atmosphere and precipitation for the calendar year 2008 in Wrocław (SW Poland). Atmospheric air samples (collected weekly) and rainwater samples (collected after rain episodes) were analysed for CO 2 and dissolved inorganic carbon (DIC) concentrations and for δ 13C composition. The values obtained varied in the ranges: atmospheric CO 2: 337–448 ppm; δ 13C CO2 from −14.4 to −8.4‰; DIC in precipitation: 0.6–5.5 mg dm −3; δ 13C DIC from −22.2 to +0.2‰. No statistical correlation was observed between the concentration and δ 13C value of atmospheric CO 2 and DIC in precipitation. These observations contradict the commonly held assumption that atmospheric CO 2 controls the DIC in precipitation. We infer that DIC is generated in ambient air temperatures, but from other sources than the measured atmospheric CO 2. The calculated isotopic composition of a hypothetical CO 2 source for DIC forming ranges from −31.4 to −11.0‰, showing significant seasonal variations accordingly to changing anthropogenic impact and atmospheric mixing processes.