Abstract
We have developed an XRF method for the determination of trace elements in suspended particulate matter. A total of 11 elements (Al, Si, S, Cl, K, Ca, Mn, Fe, Cu, Zn, Pb) were successfully detected from the SPM on an air filter after 6 h of sampling (air volume, 6 m3) by applying secondary targets of Ti, Ge and Mo for the primary X-rays from a Gd X-ray tube. Reference filter samples were prepared by dropping the mixed element standard solutions of known chemical concentrations onto a polycarbonate filter. The obtained calibration curves were linear with square values of the correlation coefficients, R2, of 0.9491 - 0.9999 for S, K, Ca, Cr, Mn, Fe, Cu, Zn, Pb. A good matching was observed between the calibration curves and those prepared from standard reference materials of SPM (NIST SRM 2783). The minimum detection limits for S, Zn and Pb were found to be 3.6, 1.0, 3.5 ng cm−2, respectively, indicating that highly sensitive analyses were possible for these elements by the present method. This analytical method was applied to air monitoring samples measured at Tsuruhashi, Osaka city (Japan). They were conducted four times by the mission of FECOA during 2006 and 2007. The trace-element levels for PM2.5 samples collected every 6 h by an air sampler onto filters for 5 days were determined by the present method. As a result, the diurnal variations of the concentrations (ng m−3) of S, K, Ca, Fe, Cu, Zn, Pb in the samples were successfully monitored. Especially, a strong positive correlation was observed between the concentration of S in PM2.5 and SO2 in air, and an increase in the concentration of sulfur during a west wind was observed. The results suggest that a possible source of sulfur for a PM2.5 sample seemed to exist to the west of the sampling point.
