Please see my comments  in the attached .pdf file.

The strength of this manuscript lies in its cross-laboratory comparison of the DTT assay for evaluating the oxidative potential (OP) of particulate matter. The study's objective—assessing the assay's reliability by involving a relatively large number of laboratories and identifying uncertainties—was clear and well-intentioned. However, I found the analysis of the results lacking in solid statistical foundations. Some data treatments appear arbitrary and lack justification, such as the selection of "assigned values" for bias evaluation, which raises questions about key interpretations. The manuscript can provide clearer statistical inferences, and some results, such as the COV and z-score, appear to overlap statistically, adding redundancy rather than clarity. Citations for some statements are vague, imprecise, or insufficient. While the manuscript presents common statistical values from various labs, It is unclear how these observations provide practically beneficial insights into the variation in outcomes and their underlying causes.  Some specific comments are given below. 

L99: I cannot reference the citation “WHO 2017” in the reference list. 

L 102-103: I find it difficult to precisely support the claims from the references- “Huang et al., 2022; Nicholson et al., 2022; Wilker et al.,103 2023; Zare Sakhvidi et al., 2022 “.  I did not find evidence from these studies to link PM to mortality.  I also recommend increasing the citations' precision- e.g., cite the exact reference to support the oxidative stress and inflammation in the statement. 

L 106: I don't find this reference supporting the claimed "unifying mechanism" from “Li et al., 2018”.

L 333: How do the authors determine the number of 20 here ?

L342 - 343: It is unclear to me what “values obtained for the dataset” that is suggested to jeopardize the use of the algorithm. 

L348-351:  The authors appear to arbitrarily toss the high-variance outcome.  How to justify this without compromising the statistical significance ? 

L369-373: Describing more details of the statistical method would be beneficial.