Origin of trace elements and inorganic ions in PM 10 aerosols to the South of Mexico City

Abstract

Measurements of trace metals and inorganic ions were carried out on PM 10 aerosols. Sampling was made in the southern section of downtown Mexico City. Samples were collected with an Andersen PM 10 high volume sampler, on glass fiber filters. The ions SO 4 2−, NO 3 −, Cl −, and NH 4 + were analyzed by ion chromatography, Na +, K +, Ca 2+ and Mg 2+ by flame atomic absorption spectroscopy and the trace metals using an atomic absorption spectrometer with a graphite furnace attachment. The results indicated that SO 4 2− was the most abundant ion, and with respect to trace metals, Pb had the highest concentration in spite of the fact that lead tetraethyl content in gasoline is prohibited by Mexican Federal Law. Pearson's correlation, applied to all data, showed a high correlation among SO 4 2−, NO 3 − and NH 4 +, indicating a common anthropogenic origin. In addition the correlation found between Na + and K + indicated a crustal origin. No correlation among the trace metals was found. The scatter plots showed a high neutralization of SO 4 2− and NO 3 − by NH 4 +, (NH 4) 2SO 4 and NH 4NO 3 were the major species formed. Enrichment factors were calculated using K as a reference and the results reflected the possible origins of the elements: crustal or anthropogenic. In order to gain a better insight into the origin of trace metals and major inorganic ions, a Principal Component Analysis was applied to the results for 10 elements and 4 ions, for the years 2003 and 2004. Sources of anthropogenic species, such as industries and vehicles are discussed.