In this work, Tiszenkel et al. reported measurements of NH3 and C1-C6 amines using an EtOH-CIMS equipped with a quadrupole mass filter (QMS) (Benson et al., 2010) at an urban site in Houston, TX. The ion chemistry and the methodology were well established. The calibration procedure and background checks were OK. However, only one major issue needs to be addressed before this manuscript can be accepted for publication. Previous work has shown that amides can also be detected by the EtOH-CIMS equipped with an HR-ToF-MS (Yao et al., 2016). It required at least a mass resolution of ~2500 to separate amines from amides. Amines are very photochemically active and can be oxidized swiftly into amides. It is reasonable to suspect significant amounts of amides were present in Houston, too. It is essential to assess the potential interferences from amides when measuring amines with a QMS-based EtOH-CIMS.

References:

Benson, D. R., Markovich, A., Al-Refai, M., and Lee, S. H.: A Chemical Ionization Mass Spectrometer for ambient measurements of Ammonia, Atmos. Meas. Tech., 3, 1075-1087, 10.5194/amt-3-1075-2010, 2010.

Yao, L., Wang, M. Y., Wang, X. K., Liu, Y. J., Chen, H. F., Zheng, J., Nie, W., Ding, A. J., Geng, F. H., Wang, D. F., Chen, J. M., Worsnop, D. R., and Wang, L.: Detection of atmospheric gaseous amines and amides by a high-resolution time-of-flight chemical ionization mass spectrometer with protonated ethanol reagent ions, Atmos. Chem. Phys., 16, 14527-14543, 10.5194/acp-16-14527-2016, 2016.

The manuscript  “Measurement Report : Urban  Ammonia and Amines in Houston, Texas” reports observations of ammonia and c1-c6 amines in Houston, TX made with a quadrupole mass spectrometer utilizing a protonated ethanol detection scheme, i.e. EtOH Quad-CIMS technique.   The observations were correlated with carbon dioxide which the authors interpret as indication of the ammonia and amines being emitted from pollution sources.  As both ammonia and amines showed higher levels in the afternoon, the authors claim this indicates ‘dominant gas-to-particle conversion processes taking place with the changing ambient temperatures’.  They also claim that from these observations globe models should use scaled down ammonia concentrations as a proxy for urban dimethylamine concentrations to simulate urban new particle formation processes in global models.  These are significant claims not well supported by the data or analysis presented here.  There is no particle information to substantiate that gas-to-particle conversion is occurring and the changes with ambient temperature are not due to emission changes, deposition changes, or inlet effects.  Extrapolating the correlation between ammonia and dimethylamine from these measurements from one site at 5 m for 19 days in downtown Houston to be representative of the whole Houston urban area is unsupported, let alone further extrapolating to global models. 

The EtOH Quad-CIMS technique is established in the literature, however, the details specific and relevant to this set of measurements are lacking.  The limit of detection is given but not adequately defined.  How is it estimated from a 1-minute integration time?  Is it the standard deviation of the signal? Or 2 times the standard deviation?  The sensitivity is determined from calibrations using permeation tubes.  What is the uncertainty of the permeation rate?  How is it determined?  How are they diluted and what is the uncertainty in the dilution step or steps? Why is the total estimated uncertainty not provided for any of the measurements reported here, including the carbon dioxide and nitrogen oxide measurements?  If the text reports a 1 minute 2 e-folding time as the time response, why does Fig. S2 report a 1 e-folding time of 28 seconds?

It is, also, curious that in the introduction of previous measurements made, this manuscript does not cite Nowak et al. 2010 which presents airborne observations of ammonia over Houston and the effect of ammonia plumes on new particle formation, especially given that Nowak et al. 2010 uses the same EtOH Quad-CIMS technique.  Even though Nowak et al. 2010 does not report amines it is highly relevant to the ammonia observations and the discussions presented here.

Nowak, J. B., J. A. Neuman, R. Bahreini, C. A. Brock, A. M. Middlebrook, A. G. Wollny, J. S. Holloway, J. Peischl, T. B. Ryerson, and F. C. Fehsenfeld (2010), Airborne observations of ammonia and ammonium nitrate formation over Houston, Texas, J. Geophys. Res., 115, D22304, doi:10.1029/2010JD014195

The correlations between the various observed species and temperature are difficult to ascertain from Fig. 4.  The text states (line 205) ‘Amines generally showed linear relationships with temperature, with C3 and C4 amines displaying the strongest relationships’, but the variability in the ammonia and amine observations make this difficult to see, even if one ignores the vertical bars.  Though the authors present an empirical parametrization of ammonia as a function of temperature, it is not on the figure to be evaluated visually.

The discussion from lines 211 to 219 is very difficult to follow.  It starts by stating ‘elevated temperatures generally result in heightened emissions of ammonia and amines.’ and continues to state ‘The clear temperature dependence of ammonia and amines indicates dominant gas-to-particle conversion processes’.  Emissions and gas-to-particle conversion are two very different processes.  The manuscript does not make it clear how to differentiate between those two without particle data.  It then goes on to state a previous study ‘showed an anticorrelation of these base compounds between gas and aerosol phases’.   However, there is no information on base compounds in the aerosol phase  provided here. It seems that the authors are saying that since a previous study was able to show that elevated temperatures affect gas-to-particle conversion then elevated temperatures here show the same even though this manuscript does not have the supporting data the previous study had.  This ambiguity in the argument does not support the claim in the abstract that the observations indicate dominant gas-to-particle conversion processes are taking place with changing ambient temperatures during the study.

The manuscript claims that the observed ratio of dimethylamine to ammonia should be used to parameterize urban dimethylamine concentrations in global models to simulate urban new particle formation.  This ratio comes from the fit of ammonia to C2-amines in Figure 7.  What exactly is plotted in Figure 7?  The manuscript says the measurements have a 1-minute time resolution, but Figure 7 is not plotting the 1-minute ammonia observations versus 1-minute amine observations.  It appears that the ammonia is binned by the ammine mixing ratio and then the ammonia average for each bin plotted.  Why is that and what is the rationale?  Why are the 1-minute observations not plotted against each other?  There are no horizontal bars included on the amine observations.  If the data has been binned, then the bin width should be shown.  It is assumed, though not stated that the ratio comes from the slope of the fit.  What fit is used and has there been any weighting applied, if so to which variables? 

Furthermore, lines 81-83 state ‘However, isomers of amines were still not resolved in the detection; for example, the measured C2-amines still contained dimethylamine and ethylamine. Thus, a major disadvantage of a mass spectrometer (regardless of mass resolution) is the inability to resolve/identify isomers.’  Thus, it is reasonable to conclude that the C2-amines in Fig. 7 could include ethylamine meaning the recommended parametrization is at best urban dimethylamine/ethylamine as 0.1% of ammonia.  Any recommendation to a modeling community needs to be clarified and stated clearly.

The manuscript reports observations of species not regularly measured.  However, the analysis is weak and does not support the conclusions the manuscript attempts to make.  Therefore, it should be rejected, and the analysis reconsidered and redone.