Comments attached as pdf

General comments:

This study introduces assimilating PM₂.₅ observations from AirNow and PurpleAir networks within JEDI for AQMv7, and analysized the assimilation benefits by conducting several experiments. The work is important and within the scope of GMD, and the manuscript is well-structured overall. However, there are still some concerns require to be addressed to further improve the quality of the manuscript before its publication.

Major comments：

(1) Data assimilation of PM_2.5 observations has been extensively studied. This study demonstrates the value of assimilating novel observations from PurpleAir for improving numerical air quality predictions. But the unique features or advantages of the PurpleAir network have not been fully demonstrated. It is suggested that the authors further strengthen the explanation of the novelty of this study.

Minor comments：

(1) The authors cited several webpages such as in Lines 58, 106, and 394 of the manuscript. It should be noted that web-based references have stability risks due to periodic or irregular maintenance of websites. If a cited page becomes inaccessible, for example the EPA webpage in L394, readers would be unable to verify the definition of "Regions 1–10", leading to confusion in subsequent region-based statistical analyses in the manuscript. Therefore, it is recommended that essential contextual information be incorporated in the manuscript to enhance completeness and readability. If the authors deem webpage citations necessary, the citation format should be revised to align with the requirement of the journal.

(2) Figure8 (middle row, right panel) shows an increase in MAE over the eastern U.S. Does it indicate limilations of the PA data or its assimilation in these region during the study period, and why.

(3) Figure8: The colorbar ranges in the top and bottom row of the left panel looks truncated. It is suggested to expand the colorbar range to fully capture the extent of MAE reduction. Meanwhile, it is recommended that each panel within multi-panel figures be labeled with letters (a, b, c, etc.) to facilitate clear referencing in the manuscript text.

(4) In Lines 88, 129, 211, 217: The "2.5" in "PM2.5" should be formatted as subscript to follow the convention and keep consistent with the others in the manuscript.

The manuscript titled “ PM2.5 Assimilation within JEDI for NOAA’s Regional Air Quality Model (AQMv7): Application to the September 2020 Western U.S. Wildfires” by Wang et al. with reference egusphere-2025-4098 is a valuable scientific contribution in operational aerosol assimilation, particularly for wildfire smoke events. Overall, it is very well written and provides a detailed investigation of the PM2.5 assimilation of AirNow and PurpleAir surface observations in AQMv7 for the US in September 2020. The spatio-temporal investigation of the influence on different forest lead times (1-24hours) provides interesting insights.

Overall, I suggest accepting the manuscript with the following mayor corrections (see document attached).