Upgrading of the PIXE system at ININ (Mexico) and report on elemental composition of atmospheric aerosols from 1990 in the ZMCM

A further upgrading of the PIXE system at ININ has been accomplished once some operational problems were overcome. Among these, the electronic noise picked up on the detector signal cables should be mentioned. This was drastically reduced using a technique suggested by the detector's manufacturer and a significant improvement in the signal to noise ratio was obtained. A detailed calibration was undertaken using spectroscopically 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 elemental composition determined. The samples were collected one day of every week, from January to December 1990, on 0.4 mu m Nuclepore filters using a single filter integral type sampler unit built at ININ. The 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 presented in this paper complement a former two-year study of 1988 and 1989.