The article from Coggon et al., investigates the contribution of cooking emissions to the volatile organic compounds measured in the urban area of Las Vegas, NV. The interest in the subject stands from the need to improve air quality in urban areas through a better characterization of present pollution sources. To my knowledge this is the first field study focusing on volatile organic compounds emitted from cooking. The authors identified some marker compounds using robust experimental methods (PTR-TOF-MS coupled with GC), compared cooking emissions with existing inventory emissions, and apportioned the cooking source using a positive matrix factorization analysis. I find the research outcome of great value and of interest to the atmospheric chemistry research community and in scope with the journal. I definitely recommend the article to be published, and only have some minor comments to make some points more clear to the readers.

L132. How was the sampling with the mobile laboratory conducted? How were the local emissions from the mobile lab excluded from the total VOC measured in air? A few lines to describe the sampling and how the focus drives were organized would be of interest.

L213. How were fragments considered in the final quantification of the molecules reported here? Is the dominant fragment considered or a sum of all the identified fragments?

L230. The authors use PMF analysis on two specific periods of the field campaign. Is there a particular choice of these 2 periods (meteorology or other changing factor)?

L482-487. How was the adjustment done ? Could you be more specific or rephrase this comment ?

L502. Could you provide more information on how you normalized the diurnal profiles to the impact of meteorology?

L512-513. What are the main sources and activities emitting these compounds? Are they also associated with personal care products consumption?

L597 How is the population density, number of restaurants and other activities differing between the two areas?

SI:

“In all figures and tables, we correct aldehyde sensitivities using the carbon-dependent fragmentation patterns shown in Fig. S2. First, we determine PTR-ToF-MS sensitivities using measured or estimated proton transfer rate constants as described by Sekimoto et al. (2017). We then multiply this sensitivity by the fraction of total signal attributed to the proton-transfer rate constant of the aliphatic aldehyde with the same carbon number.”

Could you add formulas to help following this part?

Fig. S8: Could you add a table with the mass list for each factor from the 5 factors solution adopted? Similarly to what is done for the factor cooking in Table S1.

Table S1. What is the individual number mass fraction and total mass in the table referring to? How are the unspeciated assessed from the total mass?

This study aims to evaluate the spatial distribution and contribution of cooking emissions to VOCs. The authors measured VOCs using PTR-ToF-MS through mobile laboratory and ground site measurements in Las Vegas, Nevada, which was the main study location. Supplemental observations were also conducted in Los Angeles, California and Boulder, Colorado. The mobile laboratory observed a significant enhancement of nonanal and octanal while parked downwind of restaurants in Los Angeles and Boulder. The species were also observed in Las Vegas during mobile measurement, and their spatial distribution was established. Moreover, this study estimates the contribution of cooking emissions' impact on urban air quality through source apportionment using PMF analysis.

The topic is relevant and important to advancing our knowledge in atmospheric chemistry, particularly the role of cooking in air quality. The combined mobile and ground measurements approach is interesting and resulted in valuable insights into the spatial distribution of cooking emissions. I have a few concerns about the approaches, results, and discussion as laid out in the comments below. Additionally, there are a few technical errors and suggestions to improve the legibility of the paper.

Overall, I recommend the acceptance of this manuscript for publication in the Journal of Atmospheric Chemistry and Physics after minor corrections.

Specific comments:

1. Methods section:
   1. It's explained that seven mobile measurements were conducted (Lines 128-130). Can this be elaborated, such as how long each drive was, what day and time, did each drive cover the whole Las Vegas area, etc.? Adding this to the Methods section will provide context when discussing observation results.
   2. I am not sure what the purpose of the LGR CO instrument (Line 221) is. I don't see a discussion about CO measurements in the subsequent sections. Was CO not measured at Jerome Mack and by mobile lab? CO is a primary emission tracer. Comparing CO and VOC measurements helps identify primary VOC and secondary factors.

1. Results and Discussion section:
   1. I would expect cooking emissions, including nonanal and octanal, to be elevated when the mobile lab was sampling stationary near a restaurant (Fig. 2; Lines 255-258). What I am curious about is if there was any event when the nonanal and octanal were enhanced while the mobile lab was driven past restaurants? If the instrument could not detect nonanal and octanal because the vehicle emissions are dominating, the VOC spatial distribution in Fig. 3, would need to be adjusted for the vehicle emission background.
   2. The late-night drive at 21:30-01:00 looks similar to the midday 12:00-19:00 drive (Fig. 4; Lines 317-322). The late-night pattern may look more significant because the scale in Fig 4C differs from those in 4A and 4B. I agree that the mixing ratios can be lower during the midday drive due to a higher boundary layer during the day. If the focus is on the transient events rather than the absolute value, all panels can be in different scales to emphasize them.
   3. Restaurant plume observations were done in LA and Boulder instead of Las Vegas. Is there particular reasons why it wasn't done in Las Vegas? The text implies that downtown Las Vegas is dominated by hot dog restaurants emissions because of the high R^2 (= 0.82) with LA hot dog shops. This high correlation seems coincidental. Comparison with laboratory meat cooking (Klein et al., 2016)  is interesting as it suggests a broader/generic source group (Lines 389-392). However, there is no report of the R^2 of comparison between this study and Klein et al. Additionally, I would expect time series comparison with other measurements, such as CO (related to Comment 1b), for PMF factors characterization. Are there no standard air quality parameters monitoring at Jerome Mack station?
   4. VCP-dominated factors were adjusted for unresolved mass, while other factors were not (Lines 486-489). What kind of adjustment and how was the adjustment (or no adjustment) implemented for these factors?

Technical comments:

Line 110: "made in"?

Lines 137-138: The purple shades are scattered around Las Vegas and not only cover the Las Vegas Strip/Las Vegas Blv. The legend of Fig. 1 describes purple shades as an entertainment district. I'd suggest rephrasing/clarifying this part. 

Fig. 6: Error in the title of panel B.

Line 439: Fig. S4 doesn't show the composition of the mobile source factor. It shows the aromatic species measured at Jerome Mack.

Line 445: Explain PCBTF and other acronyms that haven't been explained.

Lines 447-449: I'd recommend adding a label for PCBTF in Fig. 8 Local Solvent factor profile. At the current state, it isn't clear in Fig. 8 how PCBTF is an important and main driver of the Local Solvent factor.

Lines 482-486: This is a very long sentence and will lose the audience mid-sentence.

Line 503: "contributes to total VOC"?