General comment:

In this measurement report, “Measurement report: Atmospheric new particle formation in a coastal agricultural site explained with binPMF analysis of nitrate CI-APi-TOF spectra” Olin et al. performed nitrate-CIMS measurement at a coastal site. BinPMF was applied to the CIMS data, reporting two factors- F7 and F8, with high mass-to-charge ratios factor, which explained the NPF events well. It is an interesting study, and the results appear to support the conclusion. I have some minor comments the authors may want to consider before publication. My biggest concern is the uncertainties of the measurement as it can lead to some problems when comparing the intensities of different factors.

Specifics:

Abstract. You may want to associate F7 or F8 with a more physically meaningful name, as it is hard to comprehend what is the chemistry behind F7/F8.

Line 73. Provide more details about how the instrument works in principle. E.g., how the agent ion was produced, and at what rate? What is the flow rate being sampled into the CIMS?

Line 79. Any specific reason for averaging to 600 s? Is the code open-sourced, available at what site?

Line 80. What are the errors for the m/z calibration?

Line 85-90. I assume the C value is obtained by your calibration, while P is from the literature? Just wondering if the C and P values would vary a lot over different times and with different instruments.

Line 90. I am not familiar with nitrate CIMS calibration, can you explicitly explain what “penetration efficiency” is?

Line 105. Elaborate on the uncertainties for the determination of H2SO4, HIO3, and CH4SO3.

Line 108, “Ions smaller than 169 Th were omitted because there are many organic compounds that are unlikely the key compounds in NPF and have relatively high signals possibly causing issues in the binPMF analysis” It is not clear why many organic compounds are unlikely the key compounds in NPF.

Line 121. It is not clear why X needs to be normalized and how it is normalized? Is the signal used to calculate H2SO4 concentrations normalized?

Line 125. I am slightly confused as it seems Sij is associated with moving median, but in equation (4) no median values were used. Is the a value of 1.35 a reference value from literature? Or determined by what method specifically.

Line 137. Define “substantially”. A low Q/Qexp is not necessarily the best PMF solution.

Line 145. Again, what is the uncertainty for the assumptions of similar calibration coefficient and penetration efficiency?

Line 155. Define “strong” and “weaker”. Do you mean particle number concentration?

Line 157. How was CS determined? Maybe explain it in the Method section.

Line 175. It is hard to comprehend this sentence. Define “smallest particles” and rephrase “simultaneously not elevated”

Line 193. Any data to support the statement of “(3 factor profiles having organic patterns with p = 6 or p = 7)”.

Line 280. Has NetRad been mentioned before?

Line 353. F8 and F7 may have different sensitivity in CIMS. You may need to discuss the uncertainties when comparing their intensities.

Line 354. I don’t see why it confirms the transformation from F8 to F7 as F8 decreases while F7 increases. There are other possibilities e.g., transport of pollutants with different intensities, and changes in air masses.

Line 379. “…temperature to disfavoring them…” do you specifically mean high or low temperatures?

Conclusion. You may want to make the conclusion section short, highlighting the new findings in this study.

Figure 1. What is the red ban between Dp 3-8 nm?

Figure7. The label/legends in this figure are small, you may want to make it visible at a font size of at least 8.

General comments:

In this paper, the authors investigated the new particle formation (NPF) events in a coastal agricultural site in Southwestern Finland by using a combination of a nitrate ion-based chemical-ionization mass spectrometer, and gas analyzers as well as aerosol samplers. The binned positive matrix factorization method (binPMF) was applied to the measured mass spectra, showing that eight factors could describe the time series of ambient gas and cluster composition during the NPF events. Before publication, I think there are several comments that the authors may need to consider.

1. There are several uncertainties in this study that may lead to some problems or make this study not really convincing. First, the mass errors ranged from -10 ppm to 50 ppm (Line 211), so the identification of compounds with a high molecular weight maybe not be correct. How did the authors determine the confidence levels of the identifications in Table 1? Second, the authors said that “it cannot be certainly proved that a variable is actually forming new particles or growing them by examining the correlations. There is always a possibility that a variable is only observed simultaneously with NPF events due to the similarity of its source and the source of the precursor really causing the NPF events.” I agree with the authors about this point, but does it also mean the results of this study are also based on this uncertainty? 
2. Where do the F8 compounds come from? I also think the authors need to give a map showing the sampling site and the meteorological information such as the wind speed and direction is also required to illustrate the sources of measured aerosols and gases.
3. The time profiles of F7 compounds did not correlate with F8 compounds (Figure 7), I do not understand why the F7 formed from the F8?
4. Did the authors detect halogenated organics due to the proximity of the measurement site to the sea?

Specific comments:

1. Line 9: “Values of f_F7 higher than 0.5 were typically observed during the NPF events”. However, Figure 7c showed this value is lower than 0.5 during the NPF events on May 8-11 and 17.
2. Line 75: What is the mass resolution of CIMS during the field observation?
3. Line 108: “Ions smaller than 169 Th were omitted because there are many organic compounds that are unlikely the key compounds in NPF”. However, methanesulfonic acid can also efficiently initiate NPF in the presence of small alkylamines and water (Chen et al., 2016; Dawson et al., 2012).

References:

Chen, H., Varner, M. E., Gerber, R. B. and Finlayson-Pitts, B. J.: Reactions of Methanesulfonic Acid with Amines and Ammonia as a Source of New Particles in Air, J. Phys. Chem. B, 120(8), 1526–1536, doi:10.1021/acs.jpcb.5b07433, 2016.

Dawson, M. L., Varner, M. E., Perraud, V., Ezell, M. J., Gerber, R. B. and Finlayson-Pitts, B. J.: Simplified mechanism for new particle formation from methanesulfonic acid, amines, and water via experiments and ab initio calculations, Proc. Natl. Acad. Sci. U. S. A., 109(46), 18719–18724, doi:10.1073/pnas.1211878109, 2012.