Further measurements of atmospheric carbon dioxide at Mt. Cimone, Italy: 1979-1985

This paper presents atmospheric CO₂ concentration data continuously analyzed in the period March 1979-June 1985. A graphic computer selection method has been used in order to reject highly variable hourly data affected by local sources and malfunctions of the analyzer.

The increasing trend during the time interval considered is 1.7 ppm per year; the seasonal oscillation of monthly values, whose amplitude is 13 ppm, has been fitted by a linear term (trend) and two Fourier harmonic terms. Each annual set of daily mean values has been interpolated by a least square cubic spline using 1 node every 30 days. A relation between the behaviour of selected CO₂ data and prevailing winds, “SW” (180°-290°) and “NE” (0°-90°), appears quite evident; this behaviour is also demonstrated during Sahara-dust transport episodes. During winter, “NE” winds continue the high CO₂ concentrations measured on site, while “SW” winds are characterized by lower concentrations. In summer the situation is reversed. Therefore, we can assume the presence of a meridional gradient changing sign according to the season.