Keywords: rainwater acidity, air pollution, forest fires, dry particle deposition, wet particle deposition, Mexico, physicochemical analysis, suspended particulate matter, wind action, air quality
Physicochemical analysis of rainwater and suspended matter from Toluca city and Salazar, state of Mexico
Physicochemical analysis of rainwater collected from two sites in the State of Mexico, Toluca city and the Instituto Nacional de Investigaciones Nucleares (ININ) in Salazar, was carried out. The pH was measured twice at the sampling site and in the laboratory within five minutes following the sample opening. The SO42- was quantified by a turbidimetric method. The concentration of neutralising ions, Ca2+, Na+, Mg2+ and K+ among others, was measured by atomic absorption spectrometry. Ca2+ was found to contribute to the greatest extent in neutralising the rainwater acidity, between April and June, the first stage of rainfall. A sharp decrease of Ca2+ concentration occurs from June to the end of the year. At the same time, a lowering of pH was detected. The particulate matter was previously separated and semi-quantitatively analysed by scanning electron microscopy. The elemental composition of suspended solids consisted of C, Si, Al, Ca, S and others. Particles, ranging in size from some nm to hundreds of mm, were of two kinds: non-porous, which could be blown from soil into the atmosphere by wind action; and porous, whose main source might be the forest fires that occurred in 1998 around the Toluca Valley.