RDI sampler and XRF analysis
The RDI sampler was developed and constructed at University of California-Davis. It is a cascade impactor operated at 16.7 L/min air flow rate drawn by an external pump and coupled to a 10 μm cut-point (PM10) inlet. The 8-stage RDI sampler collects particulates continuously on 8 drums in 8 size ranges (i.e., 10-5, 5-2.5, 2.5-1.15, 1.15-0.75, 0.75-0.56, 0.56-0.34, 0.34-0.26, and 0.26-0.09 μm) with programmable time resolution of 0.4 to 48 hours (corresponding to about 0.75 to 96 weeks sampling duration), which can be preset depending on the predicted particle loading.
The RDI samples collected from the field sites are analyzed by XRF using a broad-spectrum X-ray beam generated on beamline 10.3.1 at the Advanced Light Source (ALS), Lawrence Berkeley National Laboratory. The ALS XRF system is capable of high sensitivity detection of elements ranging from sodium to uranium. The XRF analysis of the RDI samples provides quantitative elemental data for approximately 28 elements. Of the 28 elements analyzed, approximately 18 were well quantified due to their sufficiently high ambient atmospheric concentration.