An uncrewed aerial system (UAS) that developed for observations of aerosol and cloud properties in the marine atmosphere was introduced in this study. Compared to the regular UAS designed for observation of vertical aerosol and cloud properties, the new UAS (Fixed Wing VTOL Rotator or FVR-55), reported to have the advantage of much longer endurance (~4 hours), much higher height ceiling (~3 km), with the ability of carrying heavier payloads (~6 kg). As the Payload equipped with commercialized instruments, the technological advances could be refer to the FVR-55 and its sampling system connected to the Payload, however, details of which was not provided clearly. In addition, the observation data was not well analyzed and weakened its credibility. Thus, before its publication, the following issues should be properly revised and improved.

Specific and technical comments:

Line 85, by using the piston engine and liquid fuel to supply power for fixed wing flight, the engine exhaust do affect the sample air in flight, especially for the cycles flight pattern. Had the authors evaluated such influence? In addition, why the   “pusher engine”could be minimize the contamination of sample air from engine exhaust?

Line 97-101, It is unclear how the sample air passed through the nose cone of the FVR-55 then bring into the payload? Figure that showing the internal structure of the nose cone and the sample lines is needed here, which is important to evaluated the particle loss in the sample lines.

Line 124-125, did the perma pure drier used here need the sheath air to take away the wet purge gas?

Line 159-162, is the multi-channel filter sampler share the same sampling line with the other instruments? If so it would compete the air mass with the MCPC and POPS which has much lower flow rate. Please explain it. In addition, what kinds of filter was used and what about the background concentration of the mentioned elements? Considering the relative low sampling flow and limited sampling time (few hours) in flight, the collected particle mass in the filter would be insufficient for the analysis of chemical species like the water soluble ions.

Line 212-213, please provided the information on how the liquid water content was retrieved here.

Line 246-247, the RH in the sample air on the bench top measurement (~60%) is different from that those in the Clear Sky payload and the Cloudy Sky payload for comparison, which could be an important factor for the difference in measurements. Please add discussion about the influence of RH in the sample air.

Line 268-269, Line 281, the author suggested the systemic difference in particle number concentration measurement likely due to the particle losses in sampling lines, could the author provide some quantitative analysis results about the particle losses?

Line 387, Table 5, During the TUTR fights, How does the author determine if the FVR-55 is inside a cloud, or under a cloud?

Line 411-415, the relationship between particle number concentration and cloud drop size showed in Figure 9 is interesting. More in-depth analysis is suggested here, at least, discussion about the different correlations under different cloudy liquid water content is needed.   

General comments:

This paper provides an overview of the engineering effort to operate a UAS for atmospheric observation from a ship and the Tillamook UAS test range. The capability development is very exciting and shows great potential for using a UAS to support the Marine atmosphere study. The paper is well written. There are excessive efforts involved with the UAS program development. However, the scientific aspect of this paper can be strengthened with major revision. The main concerns are listed below:

1. The manuscript didn't provide enough detail about the isokinetic inlet system. This inlet is the most critical component to ensure representative aerosol collection.
2. Experimental design issues
   1. It is unclear how to sample the aerosol during a cloud flight. Is there a CVI inlet? How do you prevent the small droplet from getting into the inlet and ensure only the aerosol, not small droplets passes through?
   2. How does the aerosol sampling behave during the spiral flight pattern? Does the isok inlet work properly? Usually, the isokinetic inlet works well during a leveled flight leg only.
   3. When the aircraft circling at one altitude, how do you prevent sampling the aircraft exhaust?

Specific comments:

Abstract: this UAS capability development is essential to ensure the success of the scientific study. The abstract doesn't emphasize its importance. Although the data and results are limited, there are many lessons learned that should be shared.

Section 2.2, How was the isokinetic inlet controlled? Passive or active? Please provide the characteristics of the performance and operation ranges.

Section 2.2.1, what is the sample rate for this payload? 1 Hz?

Line 159-172, what is the detection limit for the chemical analysis? How long will the flight last to provide reasonable chemical composition data?

Section 2.2.2, How does the mSEMS sample the ambient aerosol? RH range? What is the mSEMS operating condition? Such as flowrates, sampling rate, and scanning cycle?

Line 234, how do you determine the uncertainties in the bench and UAS measurements for this study? From literature?

Line 256 -258, What are the density and chemical composition values used with this study? From the in situ measurements or literature from 2002?

Line 264-266, please double-check the precision in the percentage. Can you really get +-0.86% variance?

Line 271, what size range is used for the Cloudy Sky integrated number concentration? How does it compare with the Magic CPC?

Line 278, again, what is the size range used for the DMPS/APS compared to the Cloudy Sky POPS?

Fig 2, why not include a similar 1:1 plot as Fig. 3b?

Fig 3, Does this plot compare PSAP and STAP or PSAP with miniSASP? Some errors with the labels and legend.