Seasonal and diurnal variations of d13 C and concentration of atmospheric CO2 at Parma, Italy

Abstract

The d13 C of atmospheric CO2 from discrete air samples collected at the University campus, Parma, Italy, was measured at time intervals of about five days over a period of 18 months. Some day and night samples were measured along with three daily time series to evaluate the daily variations of d13 C values and CO2 concentrations. The following patterns were revealed: (1) the least negative d13 C values show a seasonal evolution with slightly more negative values during winter and less negative values during summer. Home heating systems probably contribute to this behaviour; (2) four samples collected in downtown Parma show more negative values than those collected at the same time at the University campus, probably because of car engine pollution; (3) occasionally, quite negative d13 C values were obtained at the campus. The expansion of polluted air masses from downtown to the suburban area may be responsible for these negative events; (4) one sample showed a d13 C of -17.67. The nearby fields had been extensively manured and the contribution from organic matter fermentation may explain the exceptionally negative result; (5) the diurnal changes in d13 C are relatively low from January to May; (6) in July and September the major daily changes take place in the late evening and in the early morning and are very fast. During the night the CO2 concentration increases by no more than some 50-60%, this behaviour differing from observations by other authors in different areas; (7) the set of daily samples collected in August shows a different behaviour, clearly related to the heavy rain that lasted for several hours during the night.