Investigating Technical Solutions to Improve the Near Real Time Measurement of Low-Z Elements in Atmospheric Particulate Matter by Energy Dispersive X-Ray Fluorescence Spectroscopy

The measurement of the elemental composition of atmospheric Particulate Matter (PM) is of paramount importance in air pollution studies, providing fundamental information for identifying aerosol sources and understanding their contributions. In this context, online instruments integrating an energy-dispersive X-ray fluorescence (ED-XRF) spectrometer into an aerosol sampler offer the capability to both collect PM and perform near-real-time elemental analysis. However, these instruments face limitations, particularly in detecting low-Z elements such as Na, Mg, and Al, which are critical tracers for natural PM sources. In order to investigate potential solutions to this limitation, different technical solutions were implemented on a compact ED-XRF spectrometer that was developed for this specific purpose. The spectrometer's performance was evaluated through comparative analyses with a commercially available online metals analyzer for PM (Xact 625i) and particle induced X-ray emission (PIXE) technique. Results demonstrated greater sensitivities and lower MDLs for low-Z elements compared to a commercial online spectrometer for PM (Xact 625i) while scatterplots of measured elemental concentrations showed good correlation with both Xact 625i and PIXE. Moreover, fairly good MDLs, even if higher than those of Xact 625i, were achieved also for mid-high-Z elements. Finally, the spectrometer also demonstrated its capability to analyze PM samples collected on filters of various sizes, beyond the commonly used 47 mm diameter ones, overcoming the typical limitations of standard ED-XRF benchtop instruments.