Abstract:
Three x-ray fluorescence systems, i.e., WDX (JSX-60PA), EDX (XR200) and EDX with a proportional counter and a 0.74 GBq (20 mCi) Fe-55 source, were used in determining SO2 in air. Air samples were collected on filters impregnated with Na2CO3. Using the 3 systems the detection limits were found to be 2.0, 2.0 and 50.0 μg of sulfur on membrane filters and 5.0, 6.0 and 50.0 μg of sulfur on cellulose filters (Whatman No.42) respectively. The optimum concentration Na2CO3 was found to be about 5% by weight. Membrane filters were found to give better resolution for low concentrations but may be easily damaged when vacuum system was used. The 3 XRF systems yielded comparable results. But there was some discrepancies between the results yielded by the EDX method and the chemical method (pararosaniline) especially for low concentrations. Field test was carried out at 2 tobacco curing plants in Chiengmai Province. The 2 EDX systems yields comparable results for high concentrations but the XR200 systems was better for low concentrations. Average 24°-hr SO2 concentration in ambient air was found to be about 78 μg/m3 using the EDX system.