General comments:

This paper introduces a new design of a thermal precipitation aerosol electrometer (TAPE) and provides helpful calibration results to evaluate the performance of this new electrometer. However, the below clarifications should be made to aid the audience in understanding the approach and to evaluate the suitable parameter ranges for the application.

1. What is the motivation for designing this new electrometer? Comparing with the TSI electrometer, why do we need this TPAE?
2. Experimental design issues
   1. The singly charged assumption limits the application of this electrometer. Therefore, the author should consider adding a CPC or another SMPS in the setup to measure the charge distribution for the testing particles. Then implement that into the calculation in equations 1-3. Or at least provide the uncertainty caused by the single charge assumption.
   2. The size effect on the performance of the TPAE covered 25-200 nm. Are those results under the singly charged assumption? If so, will the charge distribution affect the result?
   3. This study didn't characterize the real concentration range of the electrometer. At least, it should give the lowest limits for reliable concentration detection for different sizes of particles.

Specific comments:

Abstract: What are the "other physical parameters"? It might be good to mention them here to emphasize the need for TAPE development.

Line 22: Is this range based on theoretical estimation or experimental confirmation? It seemed that this was only a theoretical range. If so, please provide a practical range. In addition, it is even desirable to convert it to the aerosol concentration range. Please also specify the corresponding size range.

Line 24: The evaluation used one TSI aerosol electrometer to determine another aerosol electrometer – TAPE? Why not use CPC? How does the author determine the charging state for the testing particles?

Line 27: "The effect of particle size on the above efficiency was minor for sodium chloride particles." This is not true in general. It should depend on the size range of the testing particles.

Line 55 and 58, please spell out DiSC and TEOM.

Line 73: How does the author characterize the aerosol particles as "small" or "large"? Please specify the size range.

Introduction: It is not clear what the advantages are of developing a TPAE. Will it extend the lower detection efficiency for small-size particles? Or will it cover a wide range of aerosols?

Fig. 1: Where are the thermistors? And pre-amplifier? Please add them to the figure. Will the location affect the temperature control? If so, please explain the effects. How do you maintain the thermal gradient under different environmental conditions? Are there any feedbacks to control the cooling flow or heating plate? Will the device be used in an outdoor environment?

Fig 7. Does the fitting line indicate that the efficiency is higher than 120% at 0.2? Is it realistic? Why do we have different fitting parameters for different size aerosol particles? Such as 30 for 70 nm and 26.3 for 200 nm? It is crucial to investigate the size effect on the performance of this electrometer.

Fig 8 and Fig 9, why

Several typos in the manuscript: TDAE? Should it be TPAE?

The manuscript describes the evaluation of a novel thermal precipitation based aerosol electrometer (TPAE) that simultaneously collects particles for subsequent analyses while measuring the current stemming from the deposition of charged particles. If the charge level of the particles is known, e.g. when used downstream of a DMA, the number concentration of particles can be determined. I find the device very interesting and the evaluation has thoroughly been carried out. However, I have a several major and a few minor concerns that I believe the authors should address in a revision:

Major concerns:

• It does not become very clear, what is main field of application for the device. Is it mainly to be used downstream of a DMA? This would guarantee that particles are mostly singly charged and that the number concentration can be derived from the current measurement. But then is the main purpose to collect particles for subsequent analyses or to measure particle number concentrations and/or size distributions?
• When size distributions are measured, how much does the “smearing effect” of the particle deposition inside the device due to the residence time of the particles in teh gap space between the two plates before being deposited affect the accuracy? This effect is also likely the reason for the differences observed in the dynamic responses in Figure 4.
• It is not mentioned what size range the instrument is designed for. I assume, only for particles smaller than approximately 300 nm, for which nearly size-independent thermophoretic deposition can be expected. It is also not discussed that the assumption of size-independence only holds in the free molecular and near free-molecular regime, where the thermophoretic force (see L. Waldmann and K. H. Schmitt, Aerosol Science, edited by C. N. Davies, Academic, New York, 1966) and the opposing drag force share the same size dependence.
• When the TPAE is used downstream of a DMA, the size-independence of the deposition only holds for a fixed DMA-voltage. When the voltage is ramped during size distribution measurements, the concentration and thus the representativeness of the collected sample is dependent on the particle size due to the size dependent particle charging probability.
• Why was a radial preferred over a rectangular design? While the deposition efficiency is nearly independent of particle size (with the limitations mentioned above), the radial design introduces a spatial dependence on the particle deposition, due to the decreasing flow velocity from the center to outside. This could be overcome by a rectangular design (see e.g. Azong Wara et al., J. Nanopart. Res. 11: 1611-1624, 2009)
• Why was air-cooling preferred over the more commonly used liquid cooling?
• With such rather high temperature gradients, did you check if buoyancy may affect the deposition efficiency?
• Section 4.1.2 provides only observations. I would expect to see at least some quantitative analysis, such as the t_10-90 and t_90-10 time constants of both the TSI electrometer and the TPAE.
• While the manuscript in principle well written, it would benefit from a language check by a native speaker.

Minor comments:

• Line 51: what is meant with “early generation” of TSI model 3068B? To the best of my knowledge, this model is still commercially available.
• Line 52: it should read Faraday cup, not Faraday cage
• Line 55: This paper refers to the miniDiSC, not DiSC
• Page 3, first paragraph: The Nanomater Aerosol Sampler (TSI model 3089, Dixkens et al., Aerosol Sci. Technol. 30: 438-453, 1999) is missing in the discussion. This has been developed to electrostatically sample monodisperse particles downstream of a DMA.
• Line 77: particles move in counter-direction of a thermal gradient, not in the direction.
• Line 100: it appears that height and diameter are reversed here; it should thus read …120 and 0.5 mm in diameter and height, respectively. I would also suggest the term “gap distance” rather than height.
• Line 220-225: When I calculate the temperature gradient based on the provided values, I get 265 K/cm, not 254 K/cm. Either the temperature values or the value for the gradient seems to be incorrect.