The authors discuss the recent increase in emissions of HCFC-141b derived from observed atmospheric mole fractions by two measurement networks. They discuss reasons of this increase, but can not find a clear source. Several  potential sources are discussed and mostly excluded. The paper is well written and scientifically sounds. Well founded measurements and inversion methods are presented and discussed with a solid uncertainty analyses. 

Specifics comments:

L11: The word “Therefore” does not following logically from the previous sentences. I suggest to rephrase the sentence or simply omit the word.

L74: Remove the first occurrence of “not” in the sentence.

L140-144: Emission release fractions are determined using a statistical approach. Can you explain how you distinguish between A5 and nonA5 countries? It says “as these measurements predate the non-negligible global consumption”. Does that mean that release fractions for nonA5 are determined mostly from the period 1990-2000 and for A5 after about 2010? Also, you assume that the release fractions are constant in time. This seems valid for the ‘regular’ use of HCFC-141b, but what if there is illegal production, use, or disposal? Please discuss this, maybe around lines L312-313..

L286-287: The hemispheric differences increases from 2018 to 2021. The low hemispheric difference is only seen for 2018, a single year (what I deduce from Fig 3). With a decrease in use and emissions you would expect the hemispheric difference to become smaller, but since it is now only seen in one year, I doubt it is a valid/strong argument. Please  say something about this.

P12: Caption Fig 4: From the caption it now seems that the left panel shows the consumption data and not emissions estimated from consumption data. I think you can solve this by writing “…, and from reported consumption data …”.

L330: The disposal could on average be 15 years after peak in consumption, but it will be a rather broad peak, I assume. I would mention this, since it may be a reason why an increase in HCFC-141b emissions started in 2018 (and not in 2026).

L338-340: I would rephrase this sentence. Something like, “A universal leakage rate of 20% in 2020, compared to 0.1% in 2017 would be needed to explain the observed global increase .in emissions …”.

L352-354 and L357-359: The emissions from eastern China, scaled down from the whole of China, from Fang et al. (2018) show an increase (Fig 5), but the emissions from the whole of China from Fang et al. (2019) show a decrease? This seems inconsistent? Is there separate information for the rest of China that shows an increase?

L357: Please give a reference for the “Act on Rational use …”.

L416-418: I suggest you mention here that the increase in Chinese CFC-11 emissions could only explain 40-60% of the global increase. This would support the idea that the extra emissions in part originate from regions not monitored. This connect to the statement in L440-442.

This paper provides a thorough investigation into the apparent global increase in HCFC-141b emissions.  The authors illustrate how the global decrease and increase in emissions track with the global increase and subsequent decrease of CFC-11 emissions, which HCFC-141b largely replaced.  They provide regional emissions analysis and highlight the need for increased monitoring, given the gaps in knowledge in regional emissions over much of the global south.  This is a timely paper that has important implications for monitoring adherence to the phaseout of HCFCs under the Montreal Protocol.  I recommend that this paper be published, however, there are some points that require further clarification that I’ve outlined below.

Different time periods are used for assessing changes in emissions (e.g. 2020 emissions relative to 2008 or 2017) which makes it difficult to compare across regions.  Is there a reason for this?

The authors note on line 352 that emissions from eastern China have increased from 3.7 to 7.7 Gg/yr between 2008 and 2020.  What fraction of the global increase in emissions since 2017 can be attributed to eastern China?  This would provide a useful comparison to the 40-60% of the global increase in CFC-11 emissions found in Rigby et al. 2019 attributed to the same region.

Equation 3 – this should be the square root of the sum of squares of uncertainties, no?

Line 283 – 284 – this increase is being driven by increases in the NH?  This does not come through in the figures.   I think it would be nice to add a third row to figure 3 showing the hemispheric differences so that this point comes through. 

Lines 291-293 – why is aggregated emissions here so much higher than the 3 Gg/yr reported in the conclusions over the same period? (Line 415)

Line 424 – This line does not convey that while emissions from China cannot explain all of the rise in the emissions, it does explain part of the increase.  

Line 394 – This conclusion regarding the increase in US emissions is not clear based on the figure since the observationally-derived emissions are over such a short time period.

Figure 3 – explain the shaded region around global values here. 

Figure 4 – is reported consumption data the same thing as bottom-up estimates?  Please be consistent throughout for clarity. 

Figure 6 – why does the US bottom-up estimate not have uncertainties but the Australian estimate does?

Minor:

Line 74 – an extra ‘not’ is included here.  Fix typo.

Line 382 – Add the S to HYSPLIT.