Composição química das águas de chuva em áreas tropicais continentais, Cuibá-MT: aplicação do sistema clima urbano (S.C.U.)

Avaliou-se a composição química de águas da chuva em Cuiabá-MT sob a perspectiva do Sistema Clima Urbano (S.C.U.), considerando-se as fontes emissoras, as características geográficas/topográficas da cidade, e a relação entre o homem e a natureza. O período de amostragem foi entre os dias 21/02 e 02/07 de 2006, representando o final da estação chuvosa e início da estação seca da região. No total de 38 amostras determinaram-se a acidez (medidas de pH), a condutividade elétrica e a concentração dos ânions nitrato, sulfato, cloreto, nitrito e fosfato. Também foi observada a influência do número de dias anteriores sem chuvas ao evento na variabilidade da composição química destas amostras. Os resultados mostraram que mesmo com valores de pH inferiores a 5,6, portanto, chuvas ligeiramente ácidas; as concentrações dos ânions foram baixas, indicando a existência de chuvas limpas. Para o período do estudo, pode-se considerar Cuiabá representando área continental ainda não impactada com atividades antrópicas.It is intended, in this paper, to discuss rainwater chemical composition in Cuiabá City, using the Urban Climate System (U.C.S.) perspective, considering sources emissions, topographical and geographic characteristics, and Man-Nature relationship. The samples were collected between 02/21 and 07/02/2006, which represent the end of the wet season and the beginning of the dry season. Acidity (pH measure), electric conductivity, nitrate, sulphate, chloride, nitrite and phosphate anions concentration were determined from 38 samples in which low anions concentrations were observed. These results indicate that Cuiabá City, being a continental area, has not been impacted with the acid rain phenomenon. The influence of the number of previous days without rain in the chemical composition variability was also evaluated

Correlation analyse between pH values, nitrate concentration, conductivity electric, precipitation volume and wind direction in Cuiabá City rain, Mato Grosso State, Brazil

The research about rains acidity have been done principally in industrialized regions, where observe an efect more visible of human interference result in environment that can return on society. This job intends to analyse the values of rains acidities in Cuiabá/MT - Brazil, observing correlation between pH values, nitrate concentration, conductivity electric, precipitation volume and wind direction in this city that possess a dry and wet tropical climate, with two well defined seasons, been a wet and a dry season alternate. Has been installed a rain collection equipment in Jardim Imperial area, East region of Cuiabá (LW 56\ub0 01' 33'' e LS 15\ub0 36' 40'') in open area, free of obstacle that could contaminate the samples. Initially of each rain the rain collection equipment was open, avoiding contamination by drought deposition and the pH value and conductivity electric were measure just after rain end. Right away the sample was store correctly and frozen to later chemical analysis. Were collected 43 samples between 21/09/2004 (rain initiate) to 20/01/2005. Have been measured data of pH, electric conductivity, nitrate, wind direction, precipitation volume an days without rain. The pH values varied between 4,25 to 6,45, been 25,6% were lower than 5,0, 44,2% between 5,0 to 5,59, 20,9% between 5,60 to 6,00, and 9,3% higher than 6,01. During all months the pH average (VWM) was lower 5,6 varying between 5,04 to 5,29. The rain volume varied between 0,1 to 62,0 mm, the total rain volume in this period was 586,5 mm. Predominant wind direction was WSW that has occurred in 12 events. To analyze these data, was codify wind direction using two values, where number zero was utilized when the wind direction origin could not influence results, and one when the wind direction origin could influence data results, like wind direction origin from downtown or industrial district. Nitrate concentration varied between lower 0,02 to 0,38 mg/l, and was possible to verify that a decreases monthly nitrate concentration, in October was 0,15 mg/l and in January was 0,03 mg/l. Days numbers without rain also were analyzed, so during these days the atmosphere can concentrate more pollutants, and have varied between 0 and 8 days without rain. Have been utilized 34 samples to calculate the correlation matrix, where was possible to find a negative correlation of -0,97068 between pH values and nitrate values, a significant inverse correlation. In the others correlations were not found good results. The nonexistence of researches about rains acidity in Cuiabá and the nonexistence of others data about rain composition do not allow major conclusions about these results.Pages: 131-13