PIXE MEASUREMENTS OF AIR PARTICULATE ELEMENTAL COMPOSITION IN THE URBAN AREA OF FLORENCE, ITALY

A streak sampler has been designed to allow continuous collection of air particulates on Nuclepore PC 0.4 μm filters for a period of one week. A time resolution of one hour is achieved. For reliable quantitative determinations of concentrations, the flow rate may be stabilized with a very simple feedback mechanism acting on the pump. The preset value is typically 20 l/h and is maintained constant to better than 5% even under extreme conditions of filter loading. PIXE measurements were performed with the 3 MeV external proton beam at the Van de Graaff accelerator of the University of Florence. With currents of 4 nA and measurement times of 3 to 5 min, the counting rate was sufficiently high that statistically significant results for Na, Al, Si, S, Cl, Ca, Fe, Cu, Zn, Br and Pb were obtained to show hourly variations. Average values for S, Pb and Br during a one-week sampling period in September 1988 were 4.3, 1.2 and 0.3 μg/m3, respectively. Comparable values in January 1989 were 12.7, 2.2 and 0.45 μg/m3 for S, Pb and Br. © 1990.