The authors present new emission factors for Methane and NOx emissions from natural gas cooking stoves in Chile and Colombia. These results can be directly used in emission inventories in Latin America and possibly elsewhere. As such this is a good and useful measurement report which should be published after some minor corrections  and addressing one major shortcoming which would increase the use of the results.   

one main shortcoming: 

The article misses an integrated emission factor for 24 hrs from a home with a gas cookstove.  From the survey it should be possible to indicate the time and amount gas combustion while cooking. This leads to a cooking-related emission factor per day. During the remainder of the time there is the constant leakage. Combined this should lead to an emission factor (cooking+leakage) for each home with a gas stove per 24 hours and standard deviation. This will be necessary to calculate annual total emissions by country and will increase the use of the results published.

General comments

• The emission factors should be mentioned in the abstract
• The authors do mention that the sampled residences were select to “represent a wide variety of socio-economic status and locations etc.” + the questionnaire, but since the sample size is so small, it would be nice to have a bit more information about how it is representative (socioeconomically, type of homes, types of stoves etc.)
• The authors mention outliers that skew the data. I know it’s not always possible to explain why outliers are there, but perhaps an indication as to what it could be: is it a sampling issue, or related to the stove itself, or unclear.
• Line 31 and 52, statements suggest using natural gas is not a good choice for cooking due to CH4 and NOx pollution. While minimizing these emission is important, it is necessary to stress that cooking on solid fuels is, with regard to human health, far worse. See for example WHO, 2024.  https://www.who.int/news-room/fact-sheets/detail/household-air-pollution-and-health#:~:text=Around%202.1%20billion%20people%20worldwide,fuels%20and%20technologies%20in%20homes  This does not reduce the need for good emission factors for cooking on natural gas. But it should also not give the impression that people might as well keep cooking on wood, as gas cooking leads to CH4 emission.

Detailed / technical comments

• Line 75 replace methane by total GHG; otherwise the sentence does not make sense.
• Check on using the hyphen consistently: Steady-state or steady steady state
• There is some repetition in the introduction – e.g. the third paragraph (line 77 etc) and paragraph (line 87 etc.) can be integrated and shortened. (Is the fourth paragraph necessary? It seems the intro reads as well without)
• Fig 1 increase the size of the text on all axises; change the Spanish into English (Top of figure)
• Both Discussion and Conclusion section are labeled 4.(Conclusions should be 5.)
• Last paragraph of 4. Discussion belongs in conclusions and can be integrated in the first conclusions paragraph.
• In the zenodo file please explain the abbreviation EC as in (EC_co2 (mg/min)           EC_co (mg/min)        EC_nox (mg/min)            EC_ch4 (mg/min))

This manuscript quantifies methane and NOx emission rates from residential natural gas stoves in Chile and Colombia during three operating stages: steady-state off, steady-state on, and the ignition (pulse) phase using direct measurements. The paper’s topic is well aligned with Atmospheric Chemistry and Physics. However, I have some concerns regarding the methodology and the instrument calibration procedures that could be addressed with careful editing

Major comments:

The manuscript provides a very limited description of how the instruments  were characterized and calibrated. This is particularly important when sampling trace gases under conditions involving high temperatures and large humidity variations (for example, water vapor can increase substantially in a closed-box environment during boiling experiments). Laser-based spectrometers are sensitive to changes in water vapor when reporting dry mole fractions, which can affect measurement accuracy. The authors should provide more detailed information on the calibration procedures applied for each instrument to ensure the validity and reliability of the reported data.

The composition of natural gas varies substantially on a daily/monthly basis and across regions within the distribution network. Using city-scale composition estimates from 10 to 15 years ago is unlikely to be representative of the natural gas being sampled in 2024. Given that the measurements include 1 Hz observations of methane and ethane, which are the major components of natural gas, the authors could use the observed ethane/methane ratios to better constrain the molar composition and corresponding NG flow calculations. These measurements could also help quantify the uncertainty associated with variability in natural gas composition when calculating the relevant emission factors.

The integrated emission rates of methane, CO2, and NOx per residential natural gas stove should be calculated and applied to emission inventories and future bottom-up estimates. It would also be useful to assess combustion efficiency using the measured concentrations of CO, CO2, CH​4, and C2H6. In particular, examining how combustion efficiency relates to methane emissions under steady-state operating conditions would provide valuable additional insight.

Note that the paper talked about the CO emission rate in the conclusion, but showed no data/analysis at all in the results/discussion. Please add this to the main paper. 

Minor Comments:

Abstract 35 to 40:

“We found that methane emissions from residential stoves in Bogotá and Santiago are over six times higher than the Tier 1 IPCC emission factors currently used in national inventories.”

The authors are conflating methane emissions with emission factors, which are distinct quantities. It would be helpful to clarify which specific quantity you are talking about here. Additionally, corresponding values (with associated uncertainties) should be included here.

In Abstract 40:

“Notably, continuous leaks and ignition-related emissions, which are excluded from official estimates, contribute significantly to total methane emissions.”

This sentence can be strengthened by using more precise terminology than “official estimates.” For example, “current national/local inventory estimates” would better convey that results from this study can have a broad impact on closing the emission gap. And again, relative contribution/emission rate, and associated uncertainties should be included here in the abstract.

Introduction:

The current ordering of concepts in the introduction reads disjointed. For example, around Line 60, it would be helpful to provide a brief description of natural gas composition here, rather than in the following paragraph (the first three paragraphs could potentially be combined to form a more concise and clear introduction). First, note that natural gas consists primarily of methane with smaller fractions of other hydrocarbons, and natural gas combustion produces additional greenhouse gases CO2 and other air pollutants. This would create a clearer logical flow into the later discussion of their respective climate and health impacts.

Additionally, it reads awkwardly to discuss the climate impacts of greenhouse gases without first stating how they are linked to natural gas use. The subsequent transition to “In addition, natural gas combustion generates carbon monoxide (CO), an air toxic…” therefore feels abrupt and not well connected logically.

In line 70:

If you are stating that “many” studies exist, it would be helpful to include additional citations, as only one reference is currently provided.

In line 80:

“While some studies have reported emission factors for specific countries and fuel sources (Smith et al., 1993. Lebel et al. 2022), these datasets remain limited, creating uncertainties in global emission inventories.”

The statement “these datasets remain limited” would benefit from additional clarification. It is not clear what the limitation refers to. Is it the limited number of appliances sampled, large uncertainties in the reported emission rates, restricted geographic coverage, or any other factor, like too few studies being published? Clarifying these limitations would strengthen the argument and more clearly motivate how the present study helps address the resulting uncertainties in global emission inventories.

In line 90:

It is unclear whether this statement refers only to methane emissions or whether it also applies to combustion byproducts. Seems like you are only talking about methane, but please clarify which species are being discussed to avoid ambiguity.

In line 95:

17% and 15% do not appear particularly large on their own. If the intention is to emphasize a substantial expansion, it would be helpful to provide supporting data on how rapidly these shares have changed over time, rather than citing only the current percentages.

In line 100:

When people refer to a “cleaner” fuel, they are often considering a broader range of pollutants beyond NOx, such as  PMs, CO, SO2, etc. This sentence gives the false impression that natural gas is not necessarily cleaner than oil or wood.

In line 208: missing a period:”…and are likely a lower bound estimate of the true value Our results show that…”

Additionally, what is “true value” referred to here?

In line 205: What are the causes of the two outliers, and is it a reasonable judgment to exclude them?

In conclusion: Need to add some description of the analysis/value for CO emission since the authors are discussing them here.