General comments

The paper presents the sensitivity of ozone on precursor gases, anthropogenic ozone depleting gases and aerosol in the framework of a comparison of chemistry climate models. The main focus is on tropospheric ozone but results are presented only in crude integral quantities where effects often cancel out. One figure shows that the noise due to meteorology appears to be dominating in the 'time-slice' simulations (?) where correlations between ozone and temperatures even change sign arbitrarily. There is some lack of significance, especially if only the arbitrary values of the last simulation year are picked because of model dependent interannual variability like e.g. the QBO (Quasi-Biennial Oscillation) which is even not mentioned in the text.

A problem in this paper is that the figures are in a  poor quality concerning definition of the shown quantity, unclear units, ignoring conventions for axes and too many lines in a frame which cannot be distinguished  (Figs. 5 - 8). The worst of this is Fig. 2 with arbitrary z-axes (model levels?). Please use here a logarithmic pressure axis or altitude and more ticks. 

The conclusions cannot be drawn from the presented figures and should be expanded.

Specific comments

Line 18: In preindustrial atmospheres OH is not globally uniform due to seasonal variation, a latitude dependence, land sea differences, convection and land cover. This sentence is misleading and has to be improved.

Line 26: Surface temperature? Or some tropospheric average?

Line 29: Do you mean here "radiative forcing"? Or just photochemical smog reactions?

Line 30ff: What is the main result? Just noise? Please be more specific.

Line 44 or later: OH is also sensitive to absolute humidity (i.e. temperature dependent for fixed relative humidity) and CO.

Line 56ff: I miss some key references and mentioning 'NOx-limited' and 'VOC-limited'.

Table 1:  Contains 1 useless column (content can be in caption or text) but also definitions are missing (number of gridpoints, Eulerian or spectral model?). Here other important properties, e.g. chemistry module or boundary conditions (BVOC) might be included.  

Line 110 or later (line 240?): Important information concerning emissions and boundary conditions for gases like CO and CH₄ is missing, as well as a table 

containing emission inventories (references) for the used gases and aerosol particles. Some information on a subset of species is scattered over the text.

Line 186: Right wording? Do you use CO and HCHO as intermediate products of NMVOC oxidation?

Line 189: WMO, dynamical or O₃? Mention what is used, if models are different here it should be included in Table 1.

Line 194: This should also go into Table 1.

Line 215: Are these free running 'time-slice'-simulations with fixed boundary conditions for about the year 1850 without and with perturbations?

Line 221ff: It would be  good to have some list or table in an Appendix with what is included in VOC, BVOC, aer, HC and NTCF.  The assumptions in the scenarios are rather restricted, do you e.g. assume that soil and forest fire sources for NOx stay unchanged? 

Line 227: Inconsistent with line 400. Halocarbons include CFCs and HCFCs but also compounds containing bromine. CH₃Cl, CH₃Br and CCl₄ are the most important with natural emissions. What is used? I hope that for increased CFCs consistent initial conditions with upscaling are used for ClY and BrY concentrations to prevent a drift lasting decades.

Table 2: Include a row in the header with main features of the scenarios.

Line 240: Emission data here? Or in line 243? Please more details.

Line 266f: The numbers would be different for the 29^th year. Use at least a 2 year average because of QBO. This holds for all results shown later. For the greenhouse forcing the upper and mid tropospheric ozone matters more  than the surface one.

Line 276: Does this refer to troposphere or stratosphere? Austral summer? Known is the Antarctic vortex in the lower stratosphere in Austral winter as transport barrier and its relation to the present day ozone hole. Please be more precise here. This is confusing as well as the caption of Fig. 1 where the season names appear to refer to the Northern hemisphere.

Line 312ff: This cannot be seen from  Fig. 2 which is distorted for each model in a different way (see also general remarks). Here it might be useful to show  DJF and JJA seasons instead of the annual average.

Fig.3: I suppose you mean density weighted vertical average with variable tropopause and stratopause? Please specify in caption.  Better use fixed levels like 100 and 1hPa because of the radiative heating characteristics. Surfacetro? This is not a common meteorological word. Do you mean temperature of the surface layer? For scientific interpretation this figure is of rather limited value, due to compensating effects in different altitude levels from chemistry and radiation. 

Fig. 4:  Looks like noise due to meteorological variation in different altitudes. It is known from textbooks and the IPCC reports that the correlation of O₃  in different altitudes  with surface temperature  can change sign.  Please redesign or skip this figure.

Table 3: Please provide this for the stratosphere or better the lower stratosphere (below 10hPa). The total average numbers are almost useless because of compensating effects. For surface climate only the lower stratosphere matters. Here also some sentences on the Antarctic and Arctic ozone hole  formation and model differences in the HC-scenario would useful. Provide proper definition of what is shown in the caption (or refer at least to figure captions or an expanded Table 2).

Table 4: Expand caption as above.

Line 401: Isn't it PiClim-N₂O?

Line 422: Why? Wrong initialization?

Figure 5: Split into more panels, 20 curves in one panel cannot be distinguished.

Figure 6: Please use the same vertical axis for every model (log p).  The unit appears to be wrong or is a time integral meant? A tendency is always per time unit (s, day, year).

Figure 7: Please use the same vertical axis for every model.

Figure 8: Please use the same vertical axis for every model.   Rearrange the factor with power of 10 in the label of the y-axis of panel c. 

Figure 6-8: Better split into more panels.

Conclusions: You should clearly distinguish between troposphere and (lower) stratosphere. O₃ precursor gases like NOx and VOCs almost don't affect the stratosphere, except via aerosol formation which is not discussed. The uncertainty due to the lightning NOx parameterizations is a well known phenomena since decades. You might also mention that the models reproduce stratospheric ozone depletion by CFCs and N₂O.

Technical corrections

Line 226:  ' ' missing.

Line 227: Case typo?

Line 239: 'ta' listed 2 times.

Line 268: Isn't it WMO?

General comment:

The article “Global Sensitivity of Tropospheric Ozone to Precursor Emissions in Clean and Present-Day Atmospheres: Insights from AerChemMIP Simulations” by Wang and Gao presents the sensitivity of ozone using four different simulation global models with specific parameters and specifications. The paper's main concern is the difficulties that appear from the figures' understanding. The conclusions derived from these figures should be expanded and figures should not just be explained in the text with minimal discussions. The comparisons between the models are somehow affected by the figure’s clarity.

Specific comments:

Line 15: “secondary organic aerosol”, please use “organic” in the text since the ozone is affecting mostly organic species.

Line 28: What is tropospheric O3 forcing? Please explain.

Line 77: “hydroxyl radicals (HOₓ)”, please avoid confusion

Table 1. Please build up the table in Word and not import it as a picture as it appears. Difficult to read in the tables ….. all tables. What do you mean by “sophistication of gas-phase chemistry”? please use “lat x long”. Please use units of pressure for vertical levels for the UKESM model too.

Line 275: please be more precise and consistent with spring, summer, fall vs autumn, and winter when referring to the Arctic and Antarctic for one specific year.

Figure 4 needs improvements for a better understanding. The explanations in the article body decipher figure 4, but actually, the figure itself should be explanatory for the data.

Line 400: HCFCS probably is HCFCs.

Table 3 and 4 are hard to read.

Figures 6, 7, and 8 are difficult to read and to interpret.

Please introduce in the text Figure 6a representing ozone production.

The GISS model observed a notably high concentration of NOx at around 500 hPa altitude. Could the authors link this variation with other compounds whose concentration is induced by NOx (i.e. HONO)? Has been observed these insides of elevated NOx correlated with other chemicals?

Technical:

Line 226: concentrations.HC

Line: 256: (Shindell et al. (2006)