UPGRADING OF THE PIXE SYSTEM AT ININ (MEXICO) AND REPORT ON ELEMENTALCOMPOSITION OF ATMOSPHERIC AEROSOLS FROM 1990 IN THE ZMCM

A further upgrading of the PIXE system at ININ has been accomplished o nce some operational problems were overcome. Among these, the electron ic noise picked up on the detector signal cables should be mentioned. This was drastically reduced using a technique suggested by the detect or's manufacturer and a significant improvement in the signal to noise ratio was obtained. A detailed calibration was undertaken using spect roscopically pure thin foils of known areal density and a considerable improvement in the sensitivity of the system was achieved. Operating the upgraded system, aerosol samples were analyzed by PIXE and their e lemental composition determined. The samples were collected one day of every week, from January to December 1990, on 0.4 mu m Nuclepore filt ers using a single filter integral type sampler unit built at ININ. Th e sampling site is located in the west central part of the urban area of Mexico City (ZMCM). Temporal variations in elemental concentrations were obtained for elements ranging from sulphur to lead. Results pres ented in this paper complement a former two-year study of 1988 and 198 9.