Near real-time & benchtop XRF intercomparison for PM elemental analysis on quartz and teflon filters: a case study across three European cities

Abstract. This study presents an extensive intercomparison between a benchtop X-ray fluorescence (XRF) system and near real-time XRF monitors (Xact 625 and 625i) for measuring elemental concentrations in ambient aerosols. The measurements were conducted across three locations: Athens (Greece, March 2024), Nicosia (Cyprus, March 2022–January 2023), and Dublin (Ireland, December 2022–February 2023). The primary focus was on comparing the performance of these near real-time and benchtop XRF systems for determining the elemental composition of particulate matter (PM), alongside evaluating the impact of filter substrate choice on measurement consistency. The study specifically examines the elements Si, S, Cl, K, Ca, V, Ti, Mn, Fe, Cu, Ni, Zn, Sr, and Pb. The results highlight that filter type plays a crucial role in ensuring accurate measurements when utilizing the benchtop XRF system. At the Athens site, where PTFE filters were used, the agreement between the Xact 625i and the benchtop XRF system was stronger, with slopes across the evaluated elements generally remaining closer to unity compared to the quartz substrates. In contrast, quartz fiber filters at the Dublin and Nicosia sites led to systematic deviations, especially for light elements such as S, Cl, and K, even after applying correction factors. For heavier elements like Fe, Mn, and Cu, the filter effect was less pronounced, though some variation across sites remained. Zn consistently showed good agreement, while Pb exhibited weaker correlation, possibly due to differences in the calibration curves of the two systems. Overall, this study not only evaluates instrument performance across multiple environments but also highlights how filter substrate selection impacts the comparability of these techniques, emphasizing the need for substrate-specific considerations to enhance consistency in elemental aerosol measurements.