The Authors present a new colorimetric reaction to convert NH3 to a highly absorbing dye, taking advantage of the design principles of the LOPAP technique used extensively for HONO measurements. The technique is optimized for flows, reagent concentrations, other technical considerations, and then compared against an established optical technique in a field intercomparison. Generally speaking, the basics of a good paper are present in this work. Technically speaking, the attention to detail and quality of the work are far below the expectations required for publication in Atmospheric Measurement Techniques. There are numerous flaws throughout the manuscript that need to be addressed by the addition of more data and/or the conduct of further experiments. The organization of the manuscript makes it almost impossible to follow what was done and why. The methods section is missing a large number of critical details around the instrument design and experiments reported throughout the results and discussion. The results and discussion fail to place the technique in the context of the extensive literature on instrument intercomparisons for NH3 measurements, but also the general expectations from measuring NH3 in an urban atmosphere. The introduction fails entirely to convince one that the literature has been suitably surveyed to justify the creation of this new tool. Meanwhile, the resulting atmospheric observations are interesting and compare well to the established CRDS technique, although the interpretation and quality of the comparison are quite poor. Overall, this manuscript is currently completely unsuited for publication in AMT.

Major Comments

1. Introduction: Requires a complete re-write, based on the technical comments below. Most basic techniques and metrics for making atmospheric NH3 measurements are surveyed through a single reference, if at all. Prior intercomparisons between techniques are not suitably referenced. Last, the chemistry for the conversion of NH3 to a highly absorbing dye is notably missing from the introduction. Given the long standing knowledge on this reaction, the benefits and drawbacks, as well as the typical samples that it has been applied to should be presented in detail.
2. Methods: The instrument description and supporting figure are in no way acceptable for publication. It would be impossible to reproduce this instrumentation with the level of detail provided. Even the general components of the instrument are not communicated in the written section, or in the figure caption.
   
   
   
   This section should also contain all the information about the chemicals or solvents used, how the various solutions were made and at what concentration, details on the purity/suppliers, and so on.
   
   
   
   The experimental details of the various sections of the results and discussion are also missing from the methodology and should have some description here, along with the basic motivation for each variable that had to be optimized. Flows in particular are very poorly outlined, which is surprising since so much effort was put into a recursive algorithm to autocorrect for degradation of peristaltic pump tubing.
   
   
   
   Last, the details of the field measurements need to be relocated here, alongside the experiments conducted in the field for conducting blanks and positive controls (NH3 additions).
3. Results and Discussion: Many of the tables and figures can be replaced with a single sentence to communicate the findings. These are low quality and should be removed. There are a number of figures for which the Authors likely have data, to demonstrate the performance of their instrument, which are not presented. Some tables and figure panels are presented and never discussed in the text. Substantial attention and revision throughout the results and discussion are required.
4. Results and Discussion: The intercomparison is the capstone of this work and the quality of the analysis here requires a complete overhaul. The literature (and textbooks) are replete with examples of how to obtain a lot of insight into issues with one or both instruments during an intercomparison. Not only have the Authors neglected the basic presentation of the regression, slope, and intercept, but there is also no discussion around what these findings imply based off of the hundreds (if not more) of prior reports doing the exact same kind of comparison between two analytical methodologies. This is a fatal flaw and must be corrected. Further to this, attention to the fundamental basics of reporting analytical data is not made. For example, the Authors report detection limits (without any description of how they did the calculation) of 40.5 ppt in Section 3.2 and then proceed to report measured blank values below this in Table 2. The reported detection limit has more significant digits than any of the reported blank values as well, which suggests that this concept throughout is not being properly reviewed.

Technical Comments (line by line):

Lines 1-3: The title is confusing and long. It uses a named reaction, which is not really relevant to what is being presented in the manuscript. The reaction is one that is very long established, but has no bearing on the analytical approach. Basically, a highly UV-Vis absorbing dye is obtained from an analyte which itself is a poor absorber. This is then coupled with a very long pathlength optical sample cell, to minimize the amount of analyte that can be detected, through molecular absorption methods via the Beer-Lambert Law (which is conspicuously not presented). Named reactions are outdated ways of organizing methods, which are not accessible to an atmospheric science community composed of chemists, engineers, earth scientists, and physicists (amongst many others). Reference to a named organic chemistry reaction simply reduces the impact and uptake of this work. Consider revising the title to something more concise:



Colorimetric derivatization of ambient ammonia (NH3) for detection by long path absorption photometry

Line 13: SAC is not defined at first use, which is required according to the journal guidelines.

Lines 13: ‘Berthelot reactions’ - Named reactions are often highly colonial and exclusionary. Suggest replacing all references to this reaction with ‘based on a selective colorimetric reaction to form a highly absorbing reaction product’ or something equivalent throughout the remainder of the manuscript. It would also be useful if the authors comment on the strength of UV-Vis absorption that NH4+ has compared to the indophenol blue. The only place the named reaction really is relevant is in the caption for the reaction scheme, where it can be pointed out that this reaction has been known for ~150 years.

Line 14: ‘run statically’ – What do the Authors mean by this? That the instrument is stationary while operating? Is this something that needs to be stated? Or do they mean something else? Revise for clarity.

Line 17: ‘under stable conditions’ – Do the Authors mean ‘under optimal conditions’? A final optimal method is never clearly stated anywhere in the results and discussion. Revise for clarity here and below.

Line 18: ‘varied from background contamination’ – What do you mean? The background (or blank) experiments were contaminated and set the lowest value you could measure? Based on what seems to be presented in the results and discussion, the Authors have evaluated simple reagent blanks to determine instrumental detection limits instead of method detection limits (i.e. those that include sampling clean air). This may be incorrect word selection, but overall this does not seem relevant here and background contamination should be corrected for through the conduct of the regular measurement of negative controls (which are another outstanding issue in the results and discussion) delivered to the sampling inlet.

Line 18: ‘in the current condition’ - What does this mean? In your ambient measurements? Or using the optimized parameters that follow? If you mean the latter, then get those details out of brackets and make this sentence clearer.

Line 20: ‘with another established system’ – Be specific and state that you are comparing to a commercial cavity ring down spectrometer here.

Line 21: ‘the two instruments had good correlation’ - Qualitative. This is the focus of the paper. Slope, intercept, and R2 are all necessary for the abstract.

Line 35: It does not react with the precursors, it reacts with the acid products. Revise for correctness.

Lines 37 and 39: Referencing is completely incorrect. The second instance is a very bad example of writing about another scientist’s work and citing poorly/repetitively. Revise for all citation issues throughout to meet journal guidelines.

Line 44: How is there no discussion on the sources and sinks of atmospheric NH3 in the gas phase, nor its environmental impacts? The Authors also fail to report the typical range of mixing ratios of NH3 found in various atmospheric environments, or basic controls on its abundance (e.g. diurnal or seasonal trends). The prior paragraph only discusses particles and even that is poorly reviewed from the literature. Revise.

Line 48: ‘low’ – Should be ‘biased. The NH3 eventually comes off the surface. It is participating in a reversible dynamic equilibrium. Revise.

Line 51: Improper reference formatting in another instance that needs to be fixed throughout.

Line 53: This motivation section is poor and needs to be re-written. There is extensive literature on these kinds of inlet effects and much of it can be found in AMT or ACP. Please conduct a better literature review and better represent the current state of scientific knowledge.

Line 59: ‘viscosity’ - Incorrect. And this sentence is repeating the metal issue from above with basically an identical sentence. This is very poor writing. Please revise for clarity.

Line 63: ‘high detection accuracy and a low detection limit’ - Vague and qualitative. Lots of other reports on the QCL out there that are not cited here. This work is not the seminal one.

Line 64: ‘of low concentration’ - If you do not report what they actually achieve (or what the atmospheric range actually is - another thing that has been missed in this introduction) then this is just an arbitrary statement. Revise.

Line 66: What is an 'NH3 species'? This terminology is incorrect. Revise.

Line 67: Again, there are many other much better CIMS reports out there. Do a more comprehensive literature review. This is a journal focused on atmospheric techniques and instrumentation. The review of those should be excellent. This is poor.

Line 67: ‘The sensor measurement’ - What sensor? Is this different from CIMS? Too vague. Revise.

Lines 70-71: Coated wet annular denuder. Again, the literature review is isolated to a single paper and has not drawn from the seminal works that established these techniques. There are many MANY out there that are coupled to either flow injection analysis (FIA) or ion chromatography (IC).

Line 73: This citation is also completely incorrect. The Author's last name is not properly presented here or in the bibliography.

Line 79: This is not ‘furthermore’. Present the actual reaction from figure 1 (as a series of numbered reactions, as per many other reports in this journal), and its historic development here. It has been used for decades for routine derivatization and colorimetric analysis of NH4+ in a wide variety of environmental samples (e.g. soils, environmental waters, etc). These should also be clearly presented here.

Line 86: If you are going to build a LOPAP for NH3, perhaps you ought to describe what a LOPAP is and how it works in the introduction? Seems like a large oversight.

Lines 83-90: This section of a manuscript usually provides a clear structure for the sections/experiments conducted throughout the rest of the work. Laying out the motivations, and logic connecting each, in order here will help the Authors re-organize the entire manuscript for clarity.

Line 89: Same issue here as in the abstract. What do the Authors mean by 'statically' here? That it can be set up and left to run for long periods of time? Revise.

Line 98: Do not used names for reactions. Simply present the actual reaction and you can note that it is named in the caption for the reaction scheme, if you feel it is really important. Remember, your readers are not necessarily chemists. They could be engineers, atmospheric scientists, or established chemists who have not thought about named organic reactions in decades.

Line 104: The reactions in this ‘figure’ belong in the introduction to bolster the sections already noted. Should not be a figure. This is a reaction, so denote it as one. Each step can be presented as a separate reaction in sequence. There are plenty of examples of this throughout AMT and ACP.

Lines 106-107: Revise. Explain what the glass coil does then give it the name of stripping coil.

Why are you not operating a second channel here to correct for background issues in the reagents and/or interferences from the gas samples, like the HONO or NO2 LOPAPs do? This approach is not even discussed in the results and discussion, to contextualize the limitations of this new instrumentation. This is another glaring oversight.

Line 112: ‘higher absorption efficiency’ - The experiments determining this from standard gas flows are never presented, nor the value used. A section where those are determined (this is one of many missing and high-utility figures) and reported must be added to the manuscript.

Line 114: ‘an alkaline derivatization solution’ - Vague. Be specific with all reagents throughout. Concentrations, composition, stoichiometry, etc. There should be an entire sub-section in the methods detailing all of this.

Line 115: ‘kettle’ - Kettle is the wrong word to use here. These are typically coils of tubing wrapped around a solid material of some sort, so the reaction can proceed to completion. Sometimes also a heated compartment. A kettle is a large volume pot, which is not consistent with this or the writing that follows stating exactly this. Suggest revising to 'coil' throughout the manuscript.

Lines 119-120: ‘an LED light source, and a photoelectric detector’ – Must provide all relevant details of these so this can be reproduced. Otherwise, why are you even reporting that this instrument can be constructed if the community cannot go on to make more of them?

Line 120: ‘is filtered…’ - I do not see this filter in the Figure 2 diagram. How often does this need to be replaced? More details come below, but they belong here. The figure caption needs to do a better job of identifying this easily for readers.

Line 121: ‘contamination’ - The precipitates contain your derivatization product? If yes, then this would be contamination. If no, then this is an interference from components of the sample matrix/method reagents. Use analytical chemistry terminology appropriately.

Lines 121-122: If you made the circuit and touch panel, the details are insufficient for this manuscript. Requires its own detailed section that follows the description of the LWCC.

Line 122: ‘LWCC is 100 cm’ – Optical filter for wavelength selection? Any other critical optical components missing in this description? Based on benchtop versions of this for soil extracts, the overall description here seems to be highly limited and should be expanded so all aspects of the new instrumental innovation can be assessed.

Lines 123-124: What is this standard solution used for? Calibration of the LWCC? If yes, create a separate subsection. This section is getting very disorganized at this point.

Line 128: ‘content of the air sample’ - Give units. There are a lot of ways to report gas phase concentrations out there. Seeing as most of the figures below report mixing ratios with units of ppb, then perhaps that is what should be given here (with appropriate modifications to E1)

Line 129: ‘NH3 (g/mol)’ – If you are going to give this information, then you might as well give the actual value used too.

Line 132: ‘(a constant determined by laboratory)’ – This is never presented, either the method, nor the results and determined constant. The Authors should be reporting the best value acheived here, along with a reference to the section that describes those experiments and the results/discussion section that contextualizes them.

Line 134: The caption for Figure 2 is too simplistic. This caption should be defining all the shorthand notation above at a minimum. It could also contain information on the variables that can be controlled (e.g. flow rates of gas and liquids), as well as to depict their optimized values determined in this work. There are a lot of components that are not described anywhere (e.g. things here that I assume are peristaltic pumps, but they aren't labeled or described; or whatever the empty pink box is connected to the computer?) that should be in some kind of legend.

Lines 136-140: This does not belong here. It should be part of the methods section. None of this is shown in the reaction scheme, so its relevance is VERY unclear. How is this so important that it is the first thing that needs to be mentioned? Where is the Fe coming from? One of your reagents? I do not see any description of chemicals used, suppliers, purity, concentration, solvents, etc. provided in the methods section. These all need to be added.

Do these precipitates have little effect because they can be washed out of the system? If yes, can't you simply automate an occasional washing step in this instrument?

Lines 147-148: ‘based on the former scholar’ – These reagents are used to derivatize NH4+ in numerous standard procedures in monitoring labs. If the Authors want to cite some seminal works, that is fine, but they do not need to write that this knowledge originates from scholars.

Lines 148-149: ‘and the state… initial reaction condition’ - Why is this relevant here? It does not relate to the subject of this sentence, which is describing what the stripping coil contained. Revise and make this its own sentence with a clear subject.

Line 150: ‘particulate matter filter’ - Not clearly labeled in Figure 2. Requires further description. Please add.

Lines 151-152: ‘but a large deviation … experiment’ - Maybe, but this needs to be shown factually. Adding regular assessment of the system drift through use of online sampling of zero air (or pure N2, or by turning off the gas sampling flow and analyzing the reagents only) would give a mechanism to assess this. This is fairly common in benchtop versions of this instrument, as well as in the HONO LOPAP via the second stripping coil.

Line 152: ‘the solution concentation’ - What solution concentration? From your scrubbed gas sample? I cannot tell. Please clarify.

Line 154: ‘as shown in Figure 3’ - Is this figure showing absorbance that results from the formation of precipitate? I do not think it is; based on how this is evolving. This seems to be a plot for absorbance resulting from the analysis of a calibration standard in the system, for which the flow rates and concentrations of all the reagents are also critical to report.

It is also confusing why the Authors are reporting absorbance and the raw values of I and Io. What are these actually showing that enhances the discussion?

Overall, this figure could be removed from the manuscript and simply replaced with this sentence: 'The maximum absorbance of an XX mM NH4+ standard solution was obtained at 18.75 mM OH-'.

Line 159: ‘C6H4(OH)(COOH)’ - Use the name of the reagent, not the chemical formula. All of these details belong in the methods section. The result of obtaining maximum absorbance of the target NH4+ at a minimum amount of OH- is pretty trivial optimization. It is also not convincing that the amount of NH4+ reacted in these experiments is relevant to the upper limit of what could be expected in a real atmospheric sample, which is important to demonstrate, as all values below this would also then be expected to react to completion.

Lines 163-164: Are percentage values appropriate here? Why not give the factor? That is: XX times lower.

Lines 165-168: If you are not actually measuring this, you cannot write as if you know this is true. The amount of iron-containing precipitate 'should' be minimized based  on the known chemistry of this solution system. The mechanism by which this exerts an effect on the baseline also needs to be clearly communicated (i.e. it increases absorbance by scattering or absorbing light, resulting in measurement bias).

It is also very strange that the Authors have not implemented a routine acid cleaning procedure for the system to remove these precipitates. It would interrupt the sampling for a few minutes and also give a really large benefit to the baseline maintenance. This is so commonly used as to be part of SOPs for benchtop analyses of soil extracts of NH4+, for example.

Line 172: None of the relevant details in Figure 4 are discussed. What is the source and concentration of the NH3 being sampled? Or what does high and low concentration refer to? Is this [OH-]? And why are the scales not the same on both axes? The current depiction seems to be skewing the observations. The Authors should normalize both traces so the relative drift from the initial conditions is presented, along with sufficient detail to communicate what is actually being presented in the figure. Last, they must discuss this appropriately in this section. Why is there no comparison to any literature in this section as part of the discussion?

Lines 174-176: The description here is again very hard to follow. The Authors need to make a substantial effort to define the different components of their system that require optimization, then apply that very specific terminology throughout, with the order communicated at: i) the end of the introduction, ii) in the methods, and iii) in the results and discussion. The conclusions can then synthesize the overall outcomes in the context of the literature.

Here, for example, 'content of components in the solution' could mean just about anything. Is this the target analyte, NH3? Is it specifically the [OH-] from the prior section? Is it the large reduction in all the derivatization reagent solution concentrations from the prior section?

Also, the authors need to decouple the measurement value (absorbance) from the chemical reaction details (i.e. extent of completion in converting NH3 to the final dye).

Line 179: ‘stability and detection range’ - What does this mean? Why are measurements with respect to metrics for these two terms not presented?

Line 180-181: ‘to detect low concentrations of ammonia gas’ - This is an arbitrary statement. Was a determination of the LOD made? Seems unlikely since the collection fraction has not been ascertained.

Line 184: ‘measurement range was background contamination up to…’ - This does not make sense. Another example of careless writing. Revise for correctness, using appropriate analytical chemistry and instrumentation terminology.

Line 186: First time these flows are shown without any justification/optimization shown. When/how was the collected fraction of NH3 determined? The Authors stated this was done in the lab, but it hasn't been shown yet.

This is also an inappropriate way to first present instrument detection limits. All that has been assessed, is the reaction system and LWCC detection limits and the approach is not clearly communicated. What measurement was used? How was the average signal determined? How was the noise determined? What value of signal to noise was then calculated to represent the LOD? How many replicate observations were used, at what time resolution, and did this LOD stay constant over time (in particular, was this calculated before and after the field observations, to identify bias)?

Line 189: ‘reducing the temperature’ - Temperature of what?

Line 194: There are two points outside of the linear fit in panel b. No discussion about why these are outside the limit of linearity for the instrument. Is this poor performance of the detector? Incomplete reaction of NH4+ to the dye product? Something else?

Line 195: Same issue with this figure as with Figure 3. There is no utility in presenting the measured I and I0 voltages.

The concentration of NH4+ sampled, and how it was delivered to the system, is not described/justified.

The caption does not provide sufficient detail to understand what is being presented. For example, 'concentration' in panel b could be for anything. Is this supposed to be for NH4+?

Line 196: This section should be presented before 3.2.

Line 198: What is 'chrominance'? Do you mean molecular absorption spectrophotometry?

Line 198: ‘residence time’ - Why is there no presentation of the reaction rates that underpin the required residence time in the reaction coil? No stoichiometry or flow rate optimization is presented. Even if this is directly copied from an established standard operating procedure, this should be noted, along with the concentrations and flows of all the reagents.

Line 202: ‘new type of photoelectric detection to bubbly flow’ - Why is this not presented in more detail? The writing here can also be substantially clarified.

Line 205: ‘the bump up of’ - Should be 'increase'.

Line 209: ‘chromogenic’ – Just call it a derivatization reaction to produce the colored reaction product.

Line 217: ‘consecutive measurements’ - This is an inappropriate assessment of stability. How long did these four replicates require for collection? Shouldn't these be done across at least 4 days of constant instrument operation? Or maybe even 4 weeks? If it is going to be applied to real atmospheric sampling, it is not convincing that the performance is going to be as good as these values.

Line 219: ‘showing good stability’ - No information on how the solutions were made, frequency of replacement, or sealed from absorbing ambient NH3. The details of the blank test also need to be presented. Was the inlet of the scrubbing coil overflown with clean N2 or zero air? Or was the gas sampling stopped, and a reagent blank measurement conducted?

Line 220: ‘was approximately 140 s’ - This is actually an important observation to present the measurements from. Is this response time independent of NH4+ concentration?

Line 221: ‘by Bianchi’ - Inappropriate way to do this citation. Revise.

Line 223: In Figure 6, why is a legend for each replicate appropriate, as opposed to the equation and regression coefficient for each calibration? Why is the y-axis label ‘concentration’ instead of ‘[NH4+]’? How long was each point measured for? Are there error bars that can be placed on each calibration point? Are these take into account in the regression? The lines on this figure also seem to be connecting the data points instead of representing the linear regressions, which is not useful. Revise.

Line 224: This table is not even discussed in the preceding section. Why bother presenting it? These  ‘number’ values should be converted to values for the duration in time during continuous sampling.... If this is all within a few minutes to hours, it is not particularly appropriate. Overall, the scientific quality of this table is very poor.

Lines 226-241: This all belongs in the methods section, just like any other of the hundreds of instrument intercomparisons that have been published previously. Lots of details are missing:

What was the total combined sampling flow pulled through the inlet? And what was the resulting residence time of a gas sample in this inlet? Was the field container climate controlled? To what average values (and variability)?

Line 227: Coordinates not specific enough. Please revise. Should also be located after China at the end of the sentence.

Line 230: ‘could be used to calibrate and validate other instruments’ - The data presented in Table 2 disagrees with this statement and it is not discussed. Sloppy statement, derived from a complete lack of interpretation of the intercomparison data.

Line 233: Incorrect notation for inches. Suggest using ‘in.’ or ‘ “ ‘. Also, Teflon is a trademarked name. The polymer used in most tubing is perfluoro alkoxy (PFA). Revise.

Line 234: ‘with thermo-isolation materials’ - What does this mean? Was it temperature controlled? Revise.

Line 234: ‘Teflon’ – and these are usually made of PTFE. What is the pore size? Diameter of the filter? What kind of filter holder was it put in to?

Line 238: ‘averaged to 5 min’ - Why? Shouldn't this be done at the shortest timescale possible (i.e. 30 s)? Please provide a justification.

Line 239: ‘zero point’ – This should be done at the start and end of the campaign as well. Was it? Details of how this was done are missing/insufficient. Please provide flows, gas composition, etc.

Line 239: ‘the standard gas’ - Vague and inappropriate level of detail for publication. Revise. What is the certified value? Is this NH3 in a cylinder or from a permeation device or something else? How was the certified value of the standard ascertained? How was the composition controlled/delivered? Standard addition to ambient air sample? Or provided in clean gas?

Lines 240-241: ‘so that they… ensured quality control’ - This does not make sense. How does measuring 'zero gas' maintain stability? Do you need to flush the entire sampling inlet for 40 minutes with this to get a reasonable measurement of zero? If yes, does this mean that these observations are subject to substantial inlet effects? Please provide a plot showing these time responses using the field campaign inlet at the highest time resolution possible for both instruments. This should be compared and discussed in context of the extensive literature on NH3 inlet effects and their mitigation.

Line 247: ‘which might be… both instruments’ - Blank measurements should be used to correct the observational dataset PRIOR to comparison. Why is the regression analysis not shown? Did the regression take into account the uncertainty in the measurements from each instrument (or at least the variability from averaging each from their smallest time interval to 5 minutes)? There will be a substantial y-intercept here and the slope between the two measurements is also critical to report. Revise and make sure to properly discuss those results in the context of the substantial number of other NH3 measurement intercomparisons that have been conducted previously. No context provided here at all. Not even a discussion on the range making sense, diurnal patterns, etc.

Line 249: ‘concentration at the five-minute resolution’ – It would be better to see this at the 30 s timescale, as it would provide a more appropriate assessment of instrument response time capabilities.

Line 251: ‘study could measure… accurately’ - I disagree. Should you not be delivering calibration gas to both instruments at multiple concentrations to show that they compare well? No slope and no interpretation of the intercept from the regression analysis makes this conclusion fatally flawed because it is an arbitrary declaration. This needs to be substantiated through a careful analysis of this dataset.

Line 252: ‘STD’ - What is this? Standard deviation? Is this within any single sampling of zero gas? Or has the calculation been performed across all of the replicates? How much drift was there in the SAC over time? No discussion on this, despite all the prior sections saying that the tuned parameters are necessary to prevent drift.

Line 253: ‘RSD of the standard gas within 0.76% (Table 2)’ - Table 2 can be replaced with a single sentence for each of the experiments reported. One for the blank comparisons (no discussion of the difference in values between the two instruments is a big issue here). The second sentence would describe the conditions of the calibrations.

Last, doing the calibrations at 40 ppb of NH3 is not a fair assessment of 'agreement'. This should have been done at 5, 10, 20, and 40 ppb. Instead the Authors choose the highest observation from the ambient dataset, which is a concentration where agreement between the techniques would be most easy to obtain. Lower ambient values (100 pptv to 1 ppbv) are widely reported throughout the literature to present more of an issue, but this is neither presented, nor discussed. Major revision with respect to this is required.

Line 257: These are mixing ratios, not concentrations. The point of presenting panels b and c is not clear. They are not discussed at all. Overall, these three panels are insufficient analyses of the intercompared data for publication in a peer-reviewed article. Review the literature and revise by building on prior reports. Place this work into context of those prior studies as well.

There are five blank and calibration tests noted, but I only see two gaps in the reported dataset. Add markers to the full timeseries to indicate where each of these were performed. If they were not spaced out by actual ambient observations, then there is no value in some of these replicates.

Line 260: Revise the conclusions section in its entirety based on all other changes required throughout the manuscript. This basically needs to be completely re-written since the contents of the manuscript are currently totally unacceptable for publication.

See attachment.