The manuscript “Updates and evaluation of NOAA’s online-coupled air quality model version 7 (AQMv7) within the Unified Forecast System”  provides a thorough evaluation of the updated NOAA’s air quality model version 7 (AQMv7) within the Unified Forecast System (UFS), incorporating the recent scientific improvements from the CMAQv5.4. The authors conducted two experiments in August 2023 to assess the performance of updates. The updated version (AQMv7_new) significantly improved the spatial and temporal persistent high positive biases of the ozone mixing ratios. The AQMv7_new demonstrated reduced PM2.5 in all regions of Contiguous United States (CONUS). This study indicates that the community air quality model of CMAQ could be well accommodated in the UFS-AQM framework. This manuscript is well written, and offers a valuable contribution into the evolution of NOAA’s air quality models. Therefore, it is recommended to accept this manuscript after addressing some minor revisions.

Minor Revisions:

1. Is there aerosol/chemistry feedback to the host atmospheric model in AQMv7 and AQMv7_new? 
2. The wet deposition is also very important for the aerosol and chemical processes. However, the wet deposition is not mentioned in this manuscript. What kind of wet deposition is used in AQMv7_new?
3. Lines 104-105: “while other transport terms, such as advection and diffusion, are more appropriately handed in the FV3 physics”. Please clarify whether the advection and diffusion are handled in the FV3 physics or dynamics? 
4. Line 409: replace "AQMv_new" with "AQMv7_new” for consistency. 

Overview

The paper reports on an update of the CMAQ model with respect to chemistry and dry deposition. CMAQ is used as column model as part of UFS air quality forecasting system. The model changes are described and the performance of the UFS air quality forecast with and without the CMAQ update are evaluated with surface ozone and PM2.5 concentrations over the CONUS for August 2023. The evaluation shows reduced ozone and PM2.5 concentrations with the upgrade, which means an improved performance for ozone and more mixed results for PM2.5  

General comments

The paper is clear and well written and gives a good overview of the model updates.

A considerable limitation of the the paper is the evaluation period (August 2023) of just one month in summer.  At least a winter month needs to be included to fully understand the impact of the changes for PM2.5.  After all, the UFS air quality forecasting system is an operational system that probably runs continuously over the whole year.  Also, some of the discussed changes to ozone deposition over snow can only be evaluated in a winter period. I also believe that one month is too short to derive robust statistics. So it is recommended as good scientific practise to do the evaluation evaluation for  a 3-months summer and winter period.  It is also worth considering that the chosen month was affected by wildfire emissions but none of the upgraded elements seemed to have the potential to improve the AQ forecast in a wildfire dominated situation.    

Specific comments:

L 124: Please provider more details on this aspect. Is this a deposition term or a gas-phase chemistry term ?

L 143:  Is the increase in organic aerosol and PM2.5 primarily confirmed by the evaluation with PM2.5 observations?

L 151: The impact of this change can only be demonstrated with a wintertime simulation.    

L 160: Please provide here or in table 1 information about the used land cover and vegetation data

L 216: Please provide more details on the calculation of the IOA

L 235: Including an evaluation of the meteorology is an interesting aspect and I would recommend to move some plots from the appendix to the main paper. Please confirm that the error of the meteorological fields is exactly the same for both the reference and the upgrade.  Please add more details what ozone and PM2.5 error are mostly likely to be introduced by the increased stability.  Is there a possibility that the CMAQ upgrades compensates error coming from the meteorology ?

 L 305.  Please discuss in more detail the contributions from deposition and or halogen chemistry.  I got the impression halogen chemistry is more important in coastal areas.

L 433 Please mention earlier that the fire emissions do not include an VOC, or even not other gases ?