Chemical composition of rainwater in Córdoba City, Central Argentina

GARCIA, M.G; DEPETRIS PEDRO J.

Mar del Plata

Congreso; V Congreso Iberoamericano de Física y Química Ambiental; 2008

CNEA - UNSAM

In order to determine the possible sources of solutes and variability of the chemical composition, thirty one samples of individual rain events were collected at a site located at the city of Córdoba (Argentina, 31º24´S, 64º 11´W; ca 1.3 million inhabitants) between October 2005 and June 2007. Electrical conductivity, pH, alkalinity, major ions, and trace metals were measured in the soluble fraction after filtrating with 0.22 µ pore-size cellulose filters. According with their major ion composition, most samples are of the Ca2+-HCO3- type, but some collected during the rainy season (austral summer) are of the Na+-Cl- type. Mean pH is 6.52, almost one unit higher than the pH that results from the equilibrium of rain with atmospheric CO2 (5.6), but it varies along the year, showing a decreasing trend as rainfall increases. Similarly, the concentration of all measured parameters in rainwater shows an inverse correlation with the monthly precipitation. This characteristic seems related to the frequency of rain episodes: the longer is the period without precipitation, the higher is the amount of dust accumulated in the atmosphere and also, the concentration of soluble ions. The main source of solutes in the rainwater of Córdoba appears to be associated with the leaching of atmospheric dust. The significant correlation between Ca2+ and SO42- (r2 = 0.62; p<0.05), and between Cl- and (Na+ + K+) ions (r2 = 0.71; p<0.05) suggests the important contribution from gypsum and halite dissolution. Besides, dissolved REE patterns are similar to those obtained for wind-transported dust in nearby regions (1). Anthropogenic sources are probably responsible for the levels of some trace elements measured in rain samples. The concentrations of Pb, Cd, and Ni are in the range of values determined in the rainwater from the heavily polluted city of Mexico (2), while the concentrations of Al, Mn, and Cr are significantly higher.         (1) García, M.G., Lecomte K. L., Pasquini A. I., Formica S. M., Depetris P. J. in press. Sources and mobility of dissolved REE in mountainous streams draining granitic terrains, Sierras Pampeanas de Córdoba, Argentina. Geochimica et Cosmochimica Acta, DOI: 10.1016/j.gca.2007.09.017.   (2) Báez, A., Belmont, R., García, R., Padilla, H., Torres, M.C. 2007. Chemical composition of rainwater collected at a Southwest site of Mexico City, Mexico.