Supplement of Responses of surface ozone air quality to anthropogenic nitrogen deposition in the Northern Hemisphere

Section S1 The section describes modifications we implemented to the CLM v4.5 model for better simulating the soil NOx emissions and also reducing the model LAI overestimation. These include addition of soil NOx emission and NH3 volatilization 10 processes, and an improved parameterization of nitrogen uptake by plants. We evaluate the CLM simulated results with satellite LAI observations and soil NOx emissions calculated by GEOS-Chem.

anthropogenic nitrogen deposition are comparable to predicted impacts resulting from land use change alone.
In my opinion, this manuscript is novel, logically presented, and mostly well-written. By asynchronously coupling the Community Land Model with the GEOS-Chem chemical transport model, the authors present an enlightening approach to isolating specific land-system processes on atmospheric chemistry. The results suggest that a more refined consideration of biosphere-atmosphere coupling can have appreciable impacts on atmospheric chemistry. Like any "exploratory" modeling study, it is difficult to evaluate the implications directly with observations, but I believe this manuscript points the research community in a constructive direction. This work will surely be of interest to the Atmospheric Chemistry and Physics audience. I have only minor concerns and technical corrections to suggest.
One concern I have is that the approach seems like it would be very difficult for others to reproduce, given the variety of simulations, the dependence on land and atmospheric data products, and the asynchronous coupling. The authors appear to try and address this challenge, offering to provide the measurements and model simulations upon request. I might encourage the authors to provide separately the N-deposition fields, soil-NOx emission fields, and land cover inputs in order to facilitate potential intercomparison studies with other models.
It is also regrettable to me that the changes to the CLM relating to soil NOx emissions, NH3 volatilization, and N uptake, are relegated to the Supplementary Information. I believe these modifications could be of great interest (and debate?) to both model communities, and might stimulate constructive discussions about model development. However, given that the present manuscript already presents a substantial amount of material (and given that model development is somewhat outside the scope of ACP), I understand the authors' motivations for doing so. Is it possible there is room for an Appendix to the article instead (and the figures could be retained in the Supplemental Information)? I leave this to the authors' discretion.

Interactive comment
Printer-friendly version Discussion paper Technical Corrections: line 66: remove "been" line 91: replace "relatively" with "relative" Section 2.3: It wasn't explicitly clear to me until later in the manuscript (actually, the second last sentence) that prescribed land cover/vegetation PFT/soil types in the CLM simulations with-and without anthropogenic N deposition are constant (not dynamically changing over time or between simulations). I believe this should be clarified here, since the impacts of land use change are addressed in a separate investigation. Also, what is the source of the prescribed land/vegetation cover? What time period does it represent? line 463: replace "difference" with "different". Table 1: There is a superscript "2" under Run_soilnox, but no footnote associated with it. Furthermore, I think it could be clarified further (in the footnote or in the heading) that the GEOS-Chem simulations that address the N-deposition impact on O3 are run with present-day anthropogenic emissions. (I.e. There are essentially two families of final simulations: GEOS-Chem + anthro emissions + plant cover driven by natural N deposition _VS._ GEOS-Chem + anthro emissions + plant cover driven by natural and anthropogenic N deposition.)