Chemical composition of rainwater in the Sinos River Basin, Southern Brazil: a source apportionment study

This study aimed to assess the chemical composition of the rainwater in three areas of different environmental impact gradients in Southern Brazil using the receptor model EPA Positive Matrix Factorization (EPA PMF 5.0). The samples were collected in a bulk sampler, from October 2012 to August 2014, in three sampling sites along with the Sinos River Basin: Caraá, Taquara, and Campo Bom. The major ions NH₄⁺, Na⁺, K⁺, Ca²⁺, Mg²⁺, F^-, Cl^-, NO₃^-, SO₄^2-, and pH were analyzed, as well as identify the main emission sources. The most abundant cations and anions were Ca²⁺, Na⁺, Cl^-, and SO₄^2-, respectively. The mean pH value in the Sinos River Basin during the study period was 6.07 ± 0.49 (5.13-7.05), which suggests inputs of alkaline species into the atmosphere. The most important neutralizing agents of sulfuric and nitric acids in the Sinos River Basin are Ca²⁺ (NF = 1.36) and NH₄⁺ (NF = 0.57). The source apportionment provided by the EPA PMF 5.0 resulted in four factors, which demonstrate the influence of anthropogenic and natural sources, in the form of (a) industry/combustion of fossil fuels (F^- and SO₄^2-), (b) marine contribution (Na⁺ and Cl^-), (c) crustal contribution (K⁺, Ca²⁺, and NO₃^-), and (d) agriculture/livestock (NH₄⁺). Therefore, this study allows a more appropriate understanding of factors that contribute to rainwater chemical composition and also to possible changes in air quality.