the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 06 Jan 2026
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–January 2023), and Dublin (Ireland, December 2022–February 2023). The focus was on evaluating the chemical composition of particulate matter (PM) and 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 generally closer to unity for most elements. 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 provides practical guidance for mitigating filter-related artifacts to enhance consistency in elemental aerosol measurements.
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- RC1: 'Comment on egusphere-2025-5977', Anonymous Referee #1, 13 Feb 2026 reply
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General comment
The paper reports a comparison of Xact measurements with offline detection of using laboratory XRF. This was done in three sites with short-term campaigns using Teflon and quartz substrates. The topic is interesting even if authors should try to discuss more the reliability of Xact. Moreover, the description of the methods and the discussion/interpretation of results should be revised in a number of different ways, see my specific comment, before considering the paper for publication.
Specific comments
Lines 25-26. Here it is reported only 14 elements even if in the methodology it is reported that both the benchtop XEF and the Xact were calibrated with a significantly larger number of elements. In addition, there is not even a case in which all 14 elements are compared. The choice of the elements investigated should be discussed in more details and explained the reasons for certain choices. For example, Al is never considered, not even for Teflon substrates, even if this an element measurable with XRF and one of the forces of XRF compared to ICP for example. It is not reported because not reliably measurable by the Xact?
Line 28. “for most elements”, actually it is reported only for 8 elements.
Lines 33-34. Not really clear if this can be achieved form this paper because this may be done comparing measurements on the two substrates with the same instrument and this was not really done systematically.
Lines 48-54. I would suggest a revision of these sentences mentioning that coal burning, especially in power plants, has been shown to have distinctive Al and Si content (Cesari et al., 2016. Atmospheric Research 182, 282-293) rather than Cl and Br that are often related to sea spray especially near the coasts.
Line 61. Greater than what? It does not seem that Xact have greater precision or identify a larger number of elements. Probably you are referring to the time resolution.
Lines 69-72. This is interesting but from this work it is not clear if this replacement is actually possible. A comment on this in the conclusions is needed.
Section 2.2.1. The LODs of several elements, especially when using quartz, are not actually due to the measured of a blank rather, to their variability (i.e. three times standard deviation of concentrations measured on blanks of similar). My question here is if the measurements shown are reported correcting for blanks or not. Furthermore, it is reported a LOD also for Si on quartz. Do you believe that this element can be measured on such substrate if concentrations are larger than LOD? I am not convinced at all of this and results are not reported for this element so why to report a LOD?
Lines 215-219. Yes, light elements are less easily measurable on quartz. However, some benchtop XRF can do this al least for Na, Al, and Mg like, for example, in Potì et al. (2025, Science of the Total Environment 976, 179283). In my opinion, the part should be explained better because it could be a limitation related to the specific instruments used. Even if XAct should be able to measure Al.
Table 1 and Fig.3. It should be better to show in the figure all 8 elements. In addition, if the fits are done forcing through the origin, the R2 loose its usual meaning and it could be better to report the Pearson coefficient or the square of the Pearson coefficients.
The analysis of the effects of thickness is interesting. However, no comparison with the slopes mentioned before is reported. How these values agree with your intercomp quartz-teflon?
It is mentioned that on quartz only three elements were corrected because the other slopes were similar to one. What about the slopes of the elements not checked but reported in table 2?
Lines 338. Actually not most elements but for some that have been compared.
Conclusions. Some conclusions on the reliability of XAct should be reported as a summary comment to help in understand if it can replace benchtop instruments in the future.