ANÁLISE TEMPORAL DA COMPOSIÇÃO QUÍMICA DAS CHUVAS EM RIO VERDE - GOIÁS

Abstract

To study the atmosphere’s chemical composition is important to comprehend and control atmospheric pollution. Wet deposition can be used as an instrument for identification and quantification of elements present in the air. This study aimed to analyze rain’s chemical composition in Rio Verde, state of Goiás. The analyzes were carried out between September 2019 and December 2020. Two sample points were installed in the city, with a distance of 5.32 km between them, one in a furthest area from the urban movement (Point 1), and another point in a residential area (Point 2). Analyzes of pH, conductivity (CE), turbidity (Tb), total dissolved solids (STD) and 13 more ions (Mg2+, Ca2+, Na+, K+, Fe2+, Cu2+, Al3+, Pb2+, F-, SO4-2, NO3-, Cl-, PO43-) were performed. At Point 1 the cation concentrations decreased in the order Mg2+ > Ca2+ > Na+ > K+ > Fe2+ > Cu2+ > Al3+ > Pb2+ while at Point 2 the order was Ca2+ > Mg2+ > Na+ > K+ > Fe2+ > Cu2+ > Al3+ > Pb2+. In relation to anions, in Point 1 and 2 they presented the same order F- > SO4-2 > NO3- > Cl- > PO43-. The pH values were predominantly basic and there was little variation in this study, presenting a volume-weighted average (MPV) of 10.4 for Point 1, and 10 for Point 2. In the EC analysis, the MPV values for the two points were 36.27 and 29.5 (µS cm-1), respectively. Among the results of STD and Tbdz, all data were below the maximum limit stipulated by the Brazilian legislation for Class 1 freshwater (CONAMA 357/2005). Temperature and precipitation data were obtained through the National Institute of Meteorology (INMET) and compared with the normal climatological data from the same study period. Statistical analysis was performed using the Pearson correlation method, where at Point 1 there was a significant relationship (p < 0.01) between Tbdz × Ca+, Tbdz × CE, Tbdz × STD, SO42- × NO3-, Al3+ × NO3- and Fe2+ × Cu2+. In Point 2 the significant relationship was between: SO42- × Cu2+, Cl- × Al3+, Cl- × NO3-, F- × Pb2+, Al3+ × NO3-, Fe2+ × Pb2+, Al3+ × Mg2+, Cu2+ × Na+, Pb2+ × Mg2+, Ca+ × Tbdz, pH × CE, pH × STD and CE × STD. With this work it can be concluded that the years 2019 and 2020 were drier years and had a higher temperature than usual for the region. In addition, it was found that the ions most present in the rainwater of Rio Verde - GO are Ca+ and Mg2+, which are the source of intense agricultural activity in the region and play an important role in raising the pH values of the region's rains.