The design and characterization of a High-Performance Single-Particle Aerosol Mass Spectrometer (HP-SPAMS)
Abstract. This study describes a high-performance single-particle mass spectrometry (HP-SPAMS) design in detail. The comprehensive improvements of the injection system, optical sizing system, mass spectrometry, and data acquisition system have improved particle detection efficiency and chemical analysis. The combination of an aerodynamic particle concentrator (APC) system and a wide range of aerodynamic lenses (ADLs) enables the concentration of particles in the 100–5000 nm range by a factor of 3–5 times. The ion delayed exaction technology of bipolar time-of-flight mass spectrometry improves the mass resolution by 2~3 times, allowing the differentiation of multiple homogeneous masses of different substances. Moreover, the 4-channel data acquisition technology greatly enhances the dynamic range of mass spectrometry. The as-improved HP-SPAMS enhances the overall capability of the instrument in terms of particle detection number and detection efficiency. Moreover, it improves accuracy and sensitivity for component identification of individual particles.
The experimental performance of HP-SPAMS shows that the sizing detection efficiency of polystyrene latex microspheres is almost 70 %–100 % in the range of 300–3000 nm. Compared to the previous SPAMS, HP-SPAMS has a larger inlet flow rate, detection efficiency, and higher laser frequency, which makes HP-SPAMS increase the effective number of particles detected in the air by 47.8 times and improve the temporal resolution of detection. For the analysis of individual particles, the HP-SPAMS's improved resolution helps distinguish between most organic fragment ions and metal ions and facilitates the analysis of complex aerosol particles. For the analysis of individual particles, the increased resolution of the HP-SPAMS contributes to the differentiation of most organic fragment ions and metal ions and facilitates the evaluation of complex aerosol particles. In the case of atmospheric lead-containing particles, for example, HP-SPAMS can completely differentiate the isotopes of lead elements and the number of lead-containing particles is 145 times higher than that detected by SPAMS. The outstanding detection efficiency and chemical analysis capability of HP-SPAMS will be of great importance for low concentration aerosol detection and complex aerosol component analysis.
Xubing Du et al.
Status: final response (author comments only)
RC1: 'Comment on egusphere-2022-872', Anonymous Referee #2, 13 Nov 2022
- AC1: 'Reply on RC1', Lei Li, 04 Jan 2023
RC2: 'Review of the manuscript egusphere-2022-872 with the title: 'The design and characterization of a High-Performance Single-Particle Aerosol Mass Spectrometer (HP-SPAMS)' by Du et al.', Anonymous Referee #1, 22 Nov 2022
- AC2: 'Reply on RC2', Lei Li, 04 Jan 2023
Xubing Du et al.
Xubing Du et al.
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Review of Du et al., The design and characterization of a high-performance single-particle aerosol mass spectrometer (HP-SPAMS)
This manuscript is, as the title implies, a technical description of a single particle mass spectrometer. This is a commercial instrument, but the description is primarily technical and does not feel too much like an advertisement. It falls reasonably into the type of paper that describes the performance of a commercial instrument.
The technical specifications are in some respects quite impressive. This instrument is, for example, significantly better than the ATOFMS sold some years ago in the US by TSI, Inc. The writing is good and the references are balanced. The manuscript should be publishable with minor revisions.
One general change that would benefit the manuscript is to do fewer comparisons to the previous SPAMS instrument developed by the same group and emphasize absolute performance more. The authors are justifiably proud of their improvements, but the eventual paper should be presented for a general audience of all users of single particle mass spectrometers, not just those who own an older instrument developed/sold by the same authors. An example of something to de-emphasize or delete: “the number of lead-containing particles is 145 times higher than that detected by SPAMS” (abstract). An example of something to emphasize more: the comparison in Figure 4 of the detection efficiency of various kinds of particles, presumable due to spherical or non-spherical shapes. This is a very useful comparison between types of particles. These are just examples: there are probably dozens of places in the manuscript where the comparisons to the older SPAMS could be reduced. A few are OK, but only a few.
One important technical detail that is missing is a list of the spot sizes of the detection and ionization lasers. One cannot interpret the performance of the aerodynamic lens without knowing how big of a target is provided by the detection lasers beams. And one needs the ionization laser spot size to know the fluence available to ionize particles.
I found the discussion of the aerodynamic concentrator incorporated into the aerodynamic focusing inlet to be confusing. Maybe because it is incorporated into the inlet, it was never clear to me what the baseline was for its performance. In the abstract it says that it “enables concentration… but a factor of 3-5 times”. Compared to what? And then in section 3.1 I was not clear in the discussion of detection efficiency what the maximum detection efficiency should be. Should it be 100%? Or perhaps the maximum should be 300 to 500%, because the best possible performance would be 100%, but the concentrator would then multiply that by 3 to 5? I think a clear definition of how the baseline is defined would solve these. By the way, incorporating the aerosol concentrator into the inlet instead of having a separate concentrator upstream looks like a clever idea with several advantages.
It would be interesting to see a few spectra on a logarithmic scale, perhaps in supplemental material, to see the dynamic range from the high range/low range digitization and whether or not that induces any artifacts.
Near line 104, the pressure would be helpful as well as the orifice diameters. I think the symbol/line labels in Figure 5 may be incorrect.