Studio della qualità delle precipitazioni in due siti della provincia di Bologna: tendenza dell'ultimo decennio

The purpose of this study was to evaluate the quality of atmospheric deposition (chemical composition and pH) in two periods 1997-99 and 2007-09, in the province of Bologna (Bologna, urban area and Ozzano, rural area). The results show, between the first and the second three-year period, a decrease of the acid species (sulfate, nitrate and nitrite) and an increase of the basic ones (calcium, sodium and magnesium), with consequently an increase in the pH of the rainwater, that has gone from neutral to alkaline. The annual atmospheric deposition decreased too: in the 1997-99 period in Bologna, the average annual deposition of SO4-2 and NO3- were 37.9 and 27.8 kg ha-1 year-1 and in Ozzano 31.7 and 34.9 kg ha-1 year-1. In the 2007-09 period in Bologna, they were 24.5 and 16.5 kg ha-1 year-1 and 27.8 and 31.3 kg ha-1 year-1 in Ozzano. In addition there are significant neutralization reactions: calcium, derived from calcareous soils and from Sahara desert, is the principal agent neutralizing the acid species.