The manuscript provides a very comprehensive description of the RAQDPS023 modeling system used by Environment and Climate Change Canada to provide air quality forecasts to the public. As such, it is a rare example of a one-stop technical and scientific documentation that allows the reader to gain an understanding of the many different aspects that go into building such a system. It is also extremely well written and structured so that despite its length it is easy to follow. I commend the authors for the care they took in compiling the references that underly the scientific formulations of RAQDPS023. This extensive list of references in conjunction with the detailed descriptions of all RAQDPS023 science processes creates a rare repository of knowledge not only about RAQDPS023 but also about the tremendous amount of effort it takes to design, implement, and operationalize air quality modeling systems more generally. My specific comments listed below are minor and/or editorial in nature.

Specific Comments:

Page 3: “Schiermeir, 1978” should be “Schiermeier, 1978”. While the doi of the scanned copy available through the ACS legacy archives (https://pubs.acs.org/doi/abs/10.1021/es60142a608) indeed mis-spelled the author’s last name, the actual scanned copy available under that doi correctly shows the last name as “Schiermeier”

Page 7, line 218 and Table 1: Consider using “horizontal domain size” instead of “horizontal grid size” since the latter could potentially be misinterpreted to refer to the size (spacing) of individual grid cells which is identical between RAQDPS023 and RDPS 8.0.0.

Page 8, line 255: Maybe change “included a small number of meteorological tracers” to “included two meteorological tracers (water vapour and cloud water)”

Page 8, line 266: Insert “and” between “meteorological” and “chemical”

Page 14, lines 454 - 456: Please clarify relative to which starting point (e.g., 10 bin GEM-MACH configuration, RAQDPS022) this modification of the numerical solution was implemented.

Page 15, line 476: Consider changing “where” to “whereas”

Page 15, lines 495 – 496: This question reveals my lack of understanding of aerosol schemes, but I was still curious what “partially activated” refers to. If there is a critical particle radius above which all aerosol particles are activated as stated on line 489, and if the two bins each represent aerosols of a discrete size, how does partial activation occur? Does each discrete size bin assume an internal distribution of particle radii, allowing a determination of the fraction of particles in a bin that exceed the critical radius above which aerosols are activated?

Page 16, line 521: Would H2O (water vapour) profiles not be available from GEM?

Page 16, lines 537 – 539: Maybe comment on the implications for SOA formation when omitting emissions of organic acids and approaching the decision of which emissions to retain solely from a reactivity point of view.

Page 26, line 877: typo, change “haf already” to “had already”

Page 27, line 898: Could you elaborate on this additional information and how it was used to adjust the inventories?

Page 28, line 942: Should this be “the usual hourly anthropogenic and biogenic emissions” instead of just “the usual hourly anthropogenic emissions”?

Page 30, lines 995 – 1001: Was there any dependency of soil NO emissions on precipitation to represent the pulsing effect described in the Yienger-Levy framework?

Page 33, line 1111: Please check if “for 900 s” is needed here. With the way the end of the sentence is written (“for 900 s for three shorter 300 s time steps”), I am not sure if the only point of the sentence is to say that a single MACH chemistry execution every 900 s still took four times longer than the combined time it took to execute three GEM 300 s physics time steps, or if there is some additional information being conveyed here.

Page 36, lines 1200 – 1211: It might be good to provide a brief summary of which emission inputs (anthropogenic and natural) were used in these MOZART-4 simulations. Did the anthropogenic emissions represent 2009 conditions? Were aircraft, lightning NO, and soil NO emissions considered? Adding such information could set the stage for the updates to LBC in RAQDPS025 and future versions discussed in later sections of the manuscript.

Pages 45, lines 1493 – 1503: Given the episodic nature of processes affecting large-scale distributions of O3, CO, and PM2.5, why did the LBC updates in RAQDPS025 still adopt an approach based on climatology? Were there any differences in the types of anthropogenic and natural emissions considered in the MOZART-4 vs. CAM-chem simulations?

Page 46, lines 1520 – 1522: Does this update eliminate any dependence on the five broad phenological seasons described in the last paragraph of Section 3.9?

General comments:

This manuscript presents the operational chemical weather forecasting system of ECCC. I would like to express my applause for the authors’ many works to summarize this. This will be beneficial to trace the entire history of modeling development in ECCC, and we can learn from this broad perspective in this manuscript. Therefore, it's unavoidable that it ends up being long. I do not have any critical concerns about its current presentation quality, but I have minor requests for improving the readability.

Specific comments:

• Abstract (after line 30): Because the Part 2 manuscript presents the modeling performances not only for PM2.5 but also for gases and depositions, it would be better to provide this relevant information, such as ADOM-2 gas-phase chemistry. The current description just relies on the aerosol.
• Lines 967-968: I understand that these emissions were not considered in RAQDPS023, but is there a rationale for excluding them from the forecasting system in Canada? Regarding the aerolian dust, I could see the discussion in the final paragraph of Section 3.12; what about other sources?
• Line 3290 (Figure 1): I would like to request an improvement in this figure. For example, RAQDPS includes various sub-components, and it could be included within this figure. As the final application (post-processing), RDAQA and UMOS-AQ are described, but the purposes for each part could be briefly described in the arrow. Moreover, the colors for RDPS and RAQDPS could be unified in Figure 2 for better presentation.

Technical points:

• Lines 321, 335, 910, 916, 1150, 1380, 1528, 1531, 1604: For Moran et al. (2025), it will be better to represent this as “a companion paper by Moran et al. (2025)” (Line 52).
• Line 520: Use a subscript for the chemical species shown in this line.
• Line 577: Use subscript “NH3”.
• Line 3263: Please define “LRT”.