Please find the referee comment in the attached pdf.

This paper developed and characterized the performance of a Portable-ToF-CIMS. This new lightweight and low-power instrument has high sensitivities and acceptable mass resolving power, allowing its great use in a range of mobile or stationary platforms for characterizing ppt level of trace gases. The authors demonstrate the performance of this instrument through short-period field measurements. This paper has important implications in atmospheric chemistry and air quality studies and therefore well within the scope of AMT. It can be recommended for publication after addressing the following comments.

Specific comments:

Lines 112-115: Can the authors provide more details on how calibration was performed, e.g., the number of data points? It looks to me that six different levels of standard gases were measured (Fig. 2a) while only four data points were used to generate the calibration curve (Fig. 2b). How would the calibration curve change if all data were included?

Line 133-135: How long would it take to power on the instrument and get a stable reagent ion signal?

Line 166-167: The correlation coefficient of the fit should be given.

Line 201-202: The authors stated that “The dynamic range (<1 pptv to > 1 ppbv), ppt-level precision and low detection limits of the instrument are evident.”. However, only normalized signals were shown in Fig. 5. The mixing ratios of these key pollutants should be provided.

Line 202-205: The morning peak of HONO started increasing at around 3 am. Is this due to automobile traffic or ground elements? Is the signal in Fig. 5b in units of ncps or pptv? If it is pptv, the HONO mixing ratio at noon time is high. Is this consistent with previous studies?

Line 211-213: The maximum mixing ratio of HONO can reach 10 ppbv. It seems like a high value. What is the typical concentration of NOx in this area?

Line 224-227: Did C6H10O5 correlate with acetonitrile, another typical tracer of biomass burning? Mixing ratios should be given in Fig. 6, just like what the authors did for Fig. S1.

Line 236-238: Are there any other VOCs emitted from grilling detected, e.g., alkanals (Klein et al., 2016)?

Technical comments:

Line 16: Iodide and Benzene should be in lowercase.

Line 41: Spell out the full term of VOC and VCP. Check out the whole manuscript for similar issues.

References:

Klein, F., Platt, S.M., Farren, N.J., Detournay, A., Bruns, E.A., Bozzetti, C., Daellenbach, K.R., Kilic, D., Kumar, N.K., Pieber, S.M., Slowik, J.G., Temime-Roussel, B., Marchand, N., Hamilton, J.F., Baltensperger, U., Prévôt, A.S.H., El Haddad, I., 2016. Characterization of Gas-Phase Organics Using Proton Transfer Reaction Time-of-Flight Mass Spectrometry: Cooking Emissions. Environ. Sci. Technol. 50, 1243-1250.