|The authors have addressed most of my major concerns, and I list below additional suggestions for the authors to strengthen the paper a bit more before publication. |
The abstract and conclusions could better convey the main findings from the paper. For example, I was surprised that the findings from Figures 10 and 11 aren’t discussed.
L47 not clear what the sensitivities are to (Asian emissions?)
L58-60 is confusing as these events aren’t occurring at the same times in the eastern US as in the western US. How much did stratospheric and transported EAS pollution influence US ozone during these events?
L498-500 Can you say anything about what this finding implies regarding problems with the model simulations?
L598-601 is confusing as Mexico is usually considered part of North America. From Figure 1 it’s clear that it is separate, but this might be worth pointing out here.
L626 stronger-than-normal-transport from where to where? And compared to what time period (i.e., what is normal?) ?
L643-644. Given the comparison with observations, is this estimate expected to be too high or better than the other models?
L659. Why is nonlinear O3 chemistry stronger outside of summer?
L697-698, also repeated L741-742 and 915-916. How exactly will the new satellite help capture high O3 and LRT events? Does it have better sensitivity of ozone near the surface?
L734 Are the PBL depths higher during the LRT episodes? This would help to convince the reader of this interpretation.
L744-749. It seems the important message here is that EAS typically isn’t contributing to the highest days, yet this doesn’t come out til 2 paragraphs later and didn’t seem to be highlighted in the abstract or conclusions. The exception of the few sites in the southwestern U.S. in L768-772 is also important to note, and it’d be even better if these impacts are quantified in the abstract/conclusions. Are these sites at higher elevation? It might be worth to report separately high elevation sites from the rest of the western sites.
L794-799. Were these captured in the Lin et al. 2012ab studies? Wondering if this applies to all global models or just the ones used here.
L808. Unless the stratospheric contribution was diagnosed in the model, this attribution to stratospheric is speculative and should be clarified as such or deleted. Is the assimilation only assimilating stratospheric ozone or total ozone? Is it somehow tracking stratospheric ozone?
L822 should be clearer that it influenced mid-tropospheric ozone over the Northeast.
L828-831. Are the mixing depths shallower here and thus don’t entrain as much free tropospheric ozone into the surface layer?
L863-868 Why not discuss the contribution to events here?
L871 How many global models?
L874-875. It’s not clear if this bottom up NOx inventory discussion applies globally or to certain regions
L885-886. Is this the forward model GEOS-Chem or the adjoint sensitivities?
L922 and elsewhere – use of “free-running”. Does this mean the models are generating their own weather and thus not expected to match specific observations? I think the authors mean simply that they aren’t doing chemical data assimilation, but I’m not sure if this is the accepted use of this term.