STUDIES ON A CHEMICAL GRADIENT OF ATMOSPHERIC DEPOSITION FROM THE PO VALLEY TO THE ALPS

Atmospheric deposition was sampled at six stations located at differen t latitudes in north western Italy; chemical analyses showed mineral a cidity and the prevalence of sulphate, nitrate, ammonium and calcium. A comparative examination of the data collected in 1985-93 at the diff erent stations showed a regular decrease of concentrations from south to north; the gradient is linear and not dependent on altitude. This p attern is clearly correlated with the meteorology, as the study area r eceives masses of air mostly from the S.E. and S.W., i.e. from the Po Plain, one of the most densely populated and industrialized areas in I taly. On the other hand, the loads of ions from the atmosphere show ma xima in a band covering the subalpine area, because of the higher amou nts of precipitation. Seasonality of values was verified for the main ions, on the basis of the ANOVA and of the Kruskall Wallis test.