Spatio-temporal variability of anions in wet precipitation of Cuiabل, Brazil

Spatio-temporal variability in the ionic chemical composition of atmospheric precipitation samples was investigated at twenty-six points in Cuiabá city, Brazil, during three rainfall events from October 2009 to February 2010. All samples were analyzed for pH, electrical conductivity and ions: chloride (Cl−), fluoride (F−), nitrate (NO3−), sulfate (SO42 −) and phosphate (PO43 −). The spatial dependence and variability of the rainwaterʹs ionic composition were evaluated through semivariograms and kriging. A large proportion of the samples were characterized as acid rain: 80.77% of samples in October, 80.77% in December, and 65.38% in February. The average concentrations of Cl−, F−, NO3−, SO42 −and PO43 − were 4.43, 0.29, 3.78, 1.00 and 0.02 μeq L− 1, respectively. A strong correlation was observed between NO3−and SO42 − indicating a common anthropogenic origin of these anions. Maps generated by geostatistical techniques indicated that the highest anion concentrations occurred at the beginning of the rainy season in the industrial district and during periods of lower rainfall in the city center, indicating the important role of local emission sources.