Estudo da deposição atmosférica úmida no campus da Universidade Federal do Amazonas

Abstract

Atmospheric deposition (DA) is the process of transport and accumulation of pollutants on the surface. One of the main mechanisms of deposition occurs through rain, which has a slight natural acidity, pH 5.6 due to the presence of carbonic acid and traces of other acids such as HNO3. The objective of this work was to evaluate the rainwater in the Campus Senador Arthur Virgílio Filho – UFAM (CAVF) in terms of acidity, ionic composition and dissolved organic carbon, besides calculating the deposition rate of the evaluated parameters. The CAVF, located in the eastern zone of the city of Manaus, was installed in a forest fragment that is part of the Environmental Protection Area (APA) Manaós. Its neighborhood contains the industrial district and several avenues with an intense flow of light and heavy vehicles. Rain collections took place from September/2019 to February/2020 in a properly cleaned polyethylene bottle with an adapted funnel, in an area without vegetation cover. The samples were filtered with a PTFE membrane (0.45μm) and stored in a refrigerator even chemical analyses. pH and conductivity were measured by potentiometric methods. Soluble ions NO3 - , Cl- , SO4 2- , F- , PO4 3- were determined by ion chromatography and dissolved organic carbon (DOC) through the protocol for collection, preparation and analysis of samples of water and aqueous solutions provided by the National Institute for Space Research (INPE). Metals and cations were determined by the technique of inductively coupled plasma atomic emission spectrometry (ICP-AES). The rain presented a weighted average by volume (MPV) of pH of 4.95, indicating the influence of other acids in its composition, besides carbonic acid. The NO3- ion was the majority, followed by Cl-, composing a decreasing sequence of concentration in the composition of the rain: NO3 ->Cl->SO4 2->F->Na+>Ca2+>K+>Mg2+ based on the calculation of potential free acidity that checks the contribution of ions in the rain. All concentration values in this work showed great variation, showing the variability of pollutant levels in the samples. COD levels were high compared to previous work carried out in primary forest in central Amazonia, and are mainly due to biomass burning. The highest deposition rates were for COD, especially in the driest period. Among the anions, NO3

- had the highest rate of DU, constituting the main indicator of atmospheric pollution and warning of possible impacts on the flora and fauna of the CAVF. In relation to metals, the following order of concentration was obtained in the rain samples: P>Cu>Fe>Zn>Ni>Pb>Ba>Al>Cd>Li>V, being a phosphor of natural origin.