Partitioning of NH3-NH4+ in the Southeastern U.S.
Round 1
Reviewer 1 Report
Major revisions:
The study completely lacks the information about analytical methods. Which methods were used for sampling of gas and aerosol samples? Which methods were used for analysis of inorganic cations and anions? Parameters of methods, detection limits, comparison with other methods and previous studies?
The discussion should contain the comparison of results with other studies. Also the data from 2008-2016 should be compared with latest data.
Minor revisions:
- Page 1, line 39: Particulate matter can be classified as primary and secondary aerosol (not PM2.5) based on formation processes.
- Page 7-8: Every graph should contain information about temperature.
Author Response
Please see the file attached, which has our point-to-point response.
Author Response File: 
Author Response.docx
Reviewer 2 Report
The manuscript “Partitioning of NH3-NH4+ in the Southeastern U.S.” estimates the sensitivity of inorganic fine particulate matter to ammonia, sulfuric acid, and nitric acid using the ISORROPIA II model and the observations. The manuscript is overall well organized and addresses an important scientific problem. My main concern is that there are few quantitative calculations for the response of iPM2.5 to the changes in precursors, which is not common in a scientific paper. For example, the author shows that “Fig. 6 shows that the reduction of total H2SO4 was more effective to reduce the concentrations of iPM2.5; however, the reduction of total H2SO4 may lead to the increase of NO3– concentration, especially at the CTR and OLF sites (Figs. S14 and S20).” In L237-L239. Here the authors should tell us how much the iPM2.5 reduced and how much the NO3- concentration increased in response to the decrease in H2SO4. I suggest the author carefully go through the manuscript and give the quantitative calculations to support the conclusions. I recommend the manuscript be published after including the quantitative calculations.
Author Response
Please see the file attached, which has our point-to-point response.
Author Response File: Author Response.docx
Reviewer 3 Report
See attachment
Comments for author File: 
Comments.pdf
Author Response
Please see the file attached, which has our point-to-point response.
Author Response File: Author Response.docx
Reviewer 4 Report
In this study, the authors studied the response of ammonium salts formation in fine particulate matter to the reduction of total sulfate, total nitrate or total ammonium using observational data provided by SEARCH network and thermodynamic modelling. They found the obvious response of inorganic components mass loadings to the reduction of sulfate. The seasonal pattern and diurnal pattern are both discussed in various scenarios. A multi-linear regression model is also established. The study is comprehensive and provides interesting results about the possible response of emission reduction. In all, the study has practical applications but several important things need to be clarified. The manuscript at the current stage is not ready for the judgement of acceptance or not.
Here is the list of main concern:
The authors use thermodynamic modelling to predict the secondary salts formation. However, the assessment of model performance is not included. If the thermodynamic modelling cannot reproduce the ammonium salts or nitrate salts formation, the results drawn from the discussion of possible reduction will be questionable.
The discussion of GR and its response to the reduction looks questionable. Based on its definition, it is calculated from the total amount. Therefore, its response to the reduction is totally predictable based on the initial loadings only.
Figure 4-6, the authors claimed they only have 24-hour average particulate matter data in the method section, while the diurnal variations are also calculated. What’s the approach used here and how reliable that will be? And also, it’s very hard to draw information out of Figure 4-6. The authors should consider cleaning the Figures, highlighting the important trends and making them more readable.
The calculations of multi-linear regression can give some statistical evidence for the possible response, but isn’t that already reliably calculated by the thermodynamic model in the previous sections? Given the certain scenario, the response of secondary inorganic components can be modelled very efficiently and accurately (I believe that’s the main assumption for the previous sections). Unless there is some new information in this section, the purpose of this part of calculation looks redundant.
Author Response
Please see the file attached, which has our point-to-point response.
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
Major revisions:
Although authors added more required information, I still miss the comparison and discussion of measured data with other results around the world. There is lot of papers from the latest 4 years focused on NH3 and NH4+ monitoring. Only a few examples from WOS:
- 2020: Alexa, L., Mikuška, P.: Determination of ammonia/ammonium in air with cylindrical wet effluent diffusion denuder and aerosol counterflow two-jets unit. Chem. 92. 15827-15836.
- 2020: Lei, L., Conghui, X., Wang, D., He, Y., Wang, Q., Zhou, W., Hu, W., Pingquing, F., Chen, Y., Pan, X., Wang Z., Worsnop, D.R., Sun, Y.: Fine particle characterization in a coastal city in China: composition, sources, and impacts of industrial emissions. Chem. Phys. 20. 2877-2890.
- 2018: Artinano, B., Pujadas, M., Alonso-Blanco, E., Becerril-Valle, M., Coz E., Gomez-Moreno, F.J., Salvador, P., Nunez, L., Palacios, M., Diaz, E.: Real-time monitoring of atmospheric ammonia during a pollution episode in Madrid (Spain). Environ. 189. 80-88.
- 2018: Zhang, Y., Tang, A., Wang, D., Wang, Q., Benedict, K., Zhang, L., Liu, D., Li, Y., Collett Jr., J.L., Sun, Y., Liu, X.: The vertical variability of ammonia in urban Beijing, China. Chem. Phys. 18. 16385-16398.
- 2018: Elser, M., El-Haddad, I., Maasikmets, M., Bozzetti, C., Wolf, R., Ciarelli, G., Slowik, J.G., Richter, R., Teinemaa, E., Hüdling, C., Baltensperger, U., Prévot, A.S.H.: High contributions of vehicular emissions to ammonia in three European cities derived from mobile measurements. Environ. 175. 210-220.
Author Response
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Author Response File: Author Response.docx
Reviewer 2 Report
The manuscript has been improved in this version. However, I don’t think the authors' response is related to my comments. I recommend the manuscript be published on the atmosphere after including enough quantitative calculations in the manuscript.
Author Response
See the word file attached.
Author Response File: Author Response.docx
Reviewer 3 Report
Authors addressed my comments successfully in the author's response. But for some reason their responses have not been adequately reflected in the manuscript. You are not only convincing me but also readers. Before publication, I request followings:
- In the author's responses, there is no indication of corresponding revisions in the manuscript. Please indicate corresponding revisions in the author's response and revise the manuscript accordingly by making/including the revised text red (you already did for some, not all, though).
- Figure 2 through 7 in the author's response need to be included in the appropriate positions in the revised manuscript (or supplementary information).
- Include pH values for all of your thermodynamic model simulation results (Table S1). In your simulation, you should have your pH values. So, revise the text and include pH values wherever you mentioned NH3 neutralization in NH3 excess conditions in the manuscript (for example, Line 24, 68, 183, 248, and 343). Verify that whether NH3 neutralize particles fully or not by getting the pH values in NH3 excess condition and seeing if they are pH 7 or not. Are they consistent to previous works stating that the excess condition of NH3 does not necessarily means full neutralization (pH 7)?
- Include Table 1 from the author's response into Supplementary Information with the citation.
Author Response
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Author Response File: Author Response.docx
Reviewer 4 Report
The changes and response to my concern are acceptable. I recommend for the acceptance of this manuscript.
Author Response
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Author Response File: Author Response.docx
