This paper is analyzing hourly variation of NH₃ concentrations and quantifying surface NH3 concentrations and NH₃ emissions in China, using observations from GIIRS and IASI. A three parameter Gaussian function is used to fit NH₃ vertical profiles from GEOS-Chem and get information of NH₃ concentration at different heights. Surface NH3 concentrations and total NH₃ emissions are estimated based on the mass balance method and ratio from GEOS-Chem.

It was found that diurnal NH₃ concentrations are larger than nightly NH₃ concentrations. A good agreement is obtained between the ground measurements and the estimated. The NH₃ emissions range from 12.99 to 17.77 Tg N yr^-1 between 2008 and 2019 in China. The paper also discussed the uncertainties and capabilities of the method. The topics of paper fits the scope of ACP and the scientific idea is new. The article is generally well written and easy to follow. I have the following comments of the paper but I am supportive of publications if these aspects can be addressed.

Major concerns:

Please indicate the basis for the satellite data quality screening and the number of valid pixels after eliminating invalid pixels. If the proportion of remaining valid pixels is low, the study results will be misleading and appropriate data supplementation should be performed.

In the paper, two kinds of satellite observations are using to estimate surface NH₃ concentration. Figure. 3 and Figure. 7 show the differences in spatial distribution and numerical magnitude between them. Although there are problems of scale conversion, the comparison of the estimation results is of great necessity, especially at similar satellite overpass time.

Figure. 8 shows an abrupt change of surface NH₃ emissions in China during 2014-2015. The value of surface NH₃ emission is estimated around 17 Tg in 2019, which may be overestimated compared to previous findings. Its accuracy is questionable, and I suggest extending uncertainty analysis.

The quality of the figures in the paper needs to be improved, and there are errors and inconsistencies in the graphic descriptions, which should be carefully corrected.

Minor comments:

Page 2, line 32: Change "To provide a scientific basis of…" to "To provide a scientific basis for…".

Page 3, line 43: Change "Some studies have carried out…" to "Some studies have carried out conducted…".

Page 3, line 52: "China’s 53 cultivated land area accounts for only 8% of the world, but it consumes about 30% of the world’s nitrogen 54 (N) fertilizer". Please add article references.

Page 5, line 103: Change "are" to "is".

Page 7, line 126: There is a misuse of symbols in units (molec·cm^-2).

Page 8, line 151: Describe the information of sites in tabular form.

Page 9, line 168: Change "is" to "are".

Page 9, line 175: Check the following formula format.

Page 14, line 242: Description in 3.2 is not fitting to Figure. 5.

Page 15, line 248: There are any errors in Figure. 5, suggest reconstruction.

Page 20, line 304: Why is the time series of the Fengyun geostationary satellite data so short? Can you give an explanation?

Page 20, line 305: Change "are" to "is".

In this manuscript, the authors report on a study aimed at analyzing the changes of hourly NH₃ concentrations and estimating surface NH₃ concentrations and NH₃ emissions in China with top-down method. The manuscript fits into the scope of ACP and the results presented are very interesting to their readers. Overall the paper is clearly structured and generally well written. I have the following comments of the paper that should be addressed.

General comments:

1. Although the sources of uncertainty in the experiments covered are described in the limitations and outlook section, a quantitative analysis is lacking and should be added. How did you solve the problem of missing GIIRS data in the Yangtze River Basin mentioned in the constraints ?
2. I am confused about the treatment of the feedback ratio of surface NH₃ concentrations and emissions mentioned in the methodology. Is it the calculation done on an annual scale or on a monthly scale? Is it a variable value over time or a constant value? The feedback ratio should also be included as an element in the uncertainty and limitation analysis.

Minor comments:

line 247: check and modify the content in the Figure 5

line 292: The data of Figure. 8 doesn’t match the data described in the article

line 13: replace "China has largest NH₃ emissions in the world…" by "China has the largest NH₃ emissions globally…"

line 89: replace "method by using" with "method using"

line 103: Correct "are" to be " is"

line 115: replace "at high frequency" with "at high frequencies"

line 121: change "The average value of HRI is 0 with the standard deviation as 1" to be "The average value of HRI is 0 with a standard deviation of 1"

line 124: replace "from November in 2019 to October in 2020" to be "from November 2019 to October 2020"

line 139: change "product of" to be "product of the"

line 168: Correct "which is" with "which are"

line 208: replace "while for other time…." with "while NH₃ concentration … at other times"

line 208: replace "changes of"  to be "changes in"

line 214: replace "which may be also related with" by "which may also be related to"

line 215: replace "except" by "except for" and replace "have" by "has"

line 216: Correct "patterns" by "patterns are"

line 253: delete "during 2010-2015"

line 267: replace "have" by "had"

line 276: replace "change of" to be "change in"

line 305: Correct "are" to  be "is"

line 315: change "estimated" to be "estimate"

line 318: change "in" to be "from"

line 320: change "low" to be "the low"

line 325: change "occurred" to be "occur"

The study estimated the changes of hourly NH₃ concentrations, surface NH₃ concentrations and NH₃ emissions in China using the polar-orbiting satellite (IASI) and Fengyun-4 geostationary satellite. The results show NH₃ concentration in daytime was generally higher than that at night. Satellite-based NH₃ emissions ranged from 12.99-17.77 Tg N yr^-1 during 2008-2019. The manuscript is overall well organized and written. The analyses are neatly conducted and fit the scope of ACP. Before recommending publish the study, I have the following comments that I think the authors shall address to improve the manuscript.

Throughout the paper, there are issues with the use of plural vs singular and or verb tense, especially in the use of 3rd person, plural or singular. There is also extensive mixed use of past tense and present tense instead. I strongly recommend using unified tense instead, throughout the paper.

The feedback between surface NH₃ concentration and emissions was calculated by GEOS-Chem. Please describe the simulation process in detail and driven data in SI.

L56, Please further check if the value is 40%, if so, annual farmland NH₃ emission were estimated as 2.4 Tg N yr^-1 by the IPCC tier 1 guidelines?

L29, 57, what’s SO2, NOx, NH4+, and IPCC, etc.

L113, correct word ‘is’ to ‘are’, please check similar mistake throughout the manuscript.

L201, in Figure 1, check NH₃ concentrations (kg N ha^-1) or NH₃ concentrations (ppb).

L201, in Figure 1, he figure shows the 2019-2020 average or sum, please check similar mistake throughout the manuscript.

L282-283, need the data link or reference.