Dear Authors:

Thank you for revising the MS. I find your answers OK and can be considered
for publication.

However, although one referee is fine with your revision, the other referee
has still some concerns. Please find his comments below and revise the MS
accordingly.

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The authors have updated the MS using a recent version of IASI dataset. Although the authors have addressed most of my questions in the first-iteration review, I still have some concerns here.

I think minor revision is needed.

Major comments:
1. The first thing worries me is the number of valid observations in the 0.25o grid cell (as shown by Figure R5 in your response file). Most of your targeted region have less than 7 observations per grid cell per month. Many grid cells have even less than 4 observations per month. Given that NH3 concentration is quite sensitive to meteorology change, these small numbers of valid observations in each grid cell in each month make me doubt if they can represent the monthly NH3 concentration levels. In addition, Figure R5 show that the mean July NH3 error (d) is larger than the mean July NH3 VCDs (b) over most of your targeted region. Why not try a coarser spatial resolution? Say at 0.5o?

2. Section 3.4 Lake Victoria Basin region: While you claim that the increases of NH3 VCDs over this region are caused by the increasing cropped area around the lake, both the hot spots of NH3 VCDs (Figure S11) and the largest increase of NH3 VCDs (Figure 7 (c)) were found over the lake, not over the cropped areas to the north or to the south of the lake. In addition, Figure 7 (b) shows that the cropped area to the north of the lake and the NH3 VCDs have negative correlation. Can you explain why?

Dear Authors:

Thank you for revising the manuscript again. I find the revised version OK, and is in
accordance with the suggestions by the referees. I am happy to accept the manuscript now.

One suggestion I have is; instead of the key African region that you mention in the title,
you could use "selected" African regions, because we are not sure the "key" regions in
Africa and on what basis they are "the" key regions.

Many thanks and Kind regards
Jayan