EVALUATION OF FINE AIRBORNE PARTICULATE MATTER AT TOLUCA, ESTADO DE MEXICO, USING PIXE

Abstract

Fine airborne particulate matter (FAPM) samples were collected at an urban site (19° 17' 33.47" N, 99° 38' 50.55" W and 2670 m asl) in Toluca, the capital city of the State of Mexico. The samples, a total of 143, were collected every third day from March 2006 to April 2007 on Teflon® filters, with 24 h time resolution, using an U.S. EPA designation BGI PQ200 air sampler. The PIXE elemental analysis revealed the presence and the mass concentrations of 18 elements (S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, As, Se, Br, Rb, Sr and Pb), thirteen of which (S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, As) were consistently detected in most of the samples, and five of them (Se, Br, Rb, Sr and Pb) appeared occasionally. So, only those consistently detected were considered significant for the analysis. In order to verify whether the fine particulate concentrations complied with the FAPM Mexican Official Standard of 65 µg/m3, the filters were weighed before and after the sampling using a Cahn™ 33 microbalance with a 0.1 µg resolution, following the EPA procedures. The one year study was divided into three parts in accordance with the three climatic seasons identified in the city: dry-cold, dry-hot and rainy seasons. Results on the elemental and mass concentrations, as well as seasonal and time variations are presented. Correlations between concentrations of pairs of elements were also calculated, and the results obtained were found in good agreement with the enrichment factors determined for each season. Some pollution sources are suggested based on the analysis performed on the database and also from information obtained in a wide survey of the area. This paper presents the results of the first assessment of atmospheric pollution in this size of particle in this important city.