the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 08 Jul 2026
First field deployment of VIA-NO3-CIMS for molecular characterization and source apportionment of particle-phase oxygenated organic molecules in eastern China
Abstract. Secondary organic aerosol (SOA) is a major component of fine particulate matter, yet its molecular-level characterization remains challenging. Here, we systematically evaluated the performance of a Volatilization Inlet for Aerosols coupled with nitrate chemical ionization mass spectrometry (VIA-NO3-CIMS), including particle transmission, volatilization behavior, quantitative response, and operational stability. Following instrument characterization, the first field deployment of VIA-NO3-CIMS was conducted at the SORPES station in Nanjing, eastern China. A high-confidence dataset containing 1,695 particle-phase oxygenated organic molecules (OOMs) was established. The summed OOM concentration correlated strongly with AMS-derived organic aerosol concentrations (r = 0.88), demonstrating the quantitative capability of VIA–NO3–CIMS. Compared with gas-phase species, particle-phase OOMs exhibited larger carbon numbers, higher unsaturation, and lower volatility, with low-volatility compounds dominating the particle phase. Positive matrix factorization resolved seven SOA factors, including three biogenic-dominated, two anthropogenic-dominated, one regional background, and one pollution-episode factor. These factors contributed approximately 36.5 %, 35.4 %, 15.6 %, and 12.1 % of the total particle-phase OOM signal, respectively. Their molecular characteristics and temporal behaviors indicate important influences from daytime photochemistry, nighttime NO3 oxidation, regional transport, and episodic pollution accumulation. Factor contributions evolved systematically with PM2.5, with freshly formed SOA dominating under clean conditions and the pollution-episode factor becoming increasingly important as pollution levels increased, eventually dominating under the most polluted conditions. These results demonstrate that VIA-NO3-CIMS enables quantitative molecular-level characterization and source apportionment of particle-phase SOA, providing new insights into the composition and evolution of urban organic aerosols.
- Preprint
(4154 KB) - Metadata XML
-
Supplement
(25382 KB) - BibTeX
- EndNote
Status: open (until 19 Aug 2026)
- RC1: 'Comment on egusphere-2026-3647', Anonymous Referee #1, 28 Jul 2026 reply
Viewed
| HTML | XML | Total | Supplement | BibTeX | EndNote | |
|---|---|---|---|---|---|---|
| 121 | 54 | 14 | 189 | 31 | 11 | 12 |
- HTML: 121
- PDF: 54
- XML: 14
- Total: 189
- Supplement: 31
- BibTeX: 11
- EndNote: 12
Viewed (geographical distribution)
| Country | # | Views | % |
|---|
| Total: | 0 |
| HTML: | 0 |
| PDF: | 0 |
| XML: | 0 |
- 1
This study couples a VIA with NO3-CIMS and presents its first deployment for continuous measurements of ambient particles at a suburban site in Nanjing. The authors investigate particle-phase OOMs from three perspectives: molecular composition, gas–particle compositional differences, and PMF-based source apportionment. The online measurement of particle-phase highly oxygenated organic molecules at high time resolution has clear methodological value. The integration of VIA-NO3-CIMS measurements with HR-ToF-AMS, VOC, meteorological, and trajectory data also gives this dataset potentially important scientific significance. The manuscript is generally well structured and contains a comprehensive set of figures. If the key methodological issues are adequately resolved, this work could become an important case study for the application of VIA-NO3-CIMS to ambient aerosol measurements.
However, the current conclusions require more robust support from instrument characterization and statistical analyses, or alternatively, more cautious wording. I would be willing to recommend this study for publication after the issues below have been addressed.
The authors derived an empirical calibration coefficient by regressing the normalized HSO4⁻ signal measured by VIA-NO3-CIMS against particulate sulfate mass concentrations measured by the AMS, and subsequently applied this single coefficient to all detected organic molecules. This approach raises several concerns, such as the conversion efficiency of particulate sulfur-containing salts into detectable H2SO4/HSO4⁻ at 300 °C, post-evaporation wall losses, and compound-dependent NO3⁻ ionization responses for different organic molecules. The response to sulfuric acid cannot automatically be assumed to represent the responses of multifunctional organic compounds, peroxides, and organic nitrates. Moreover, the contribution of OOMs to AMS-derived SOA additionally depends on both the AMS-PMF separation of SOA and the VIA calibration. I recognize that quantifying all uncertainties associated with the VIA-NO3-CIMS analytical and quantification process, as well as the AMS-PMF analysis, is challenging. Nevertheless, I suggest that the uncertainties that can be reasonably estimated should be explicitly reported in the results. Accordingly, the statements in the manuscript (including the Abstract and Conclusions) regarding "quantitative capability" and absolute concentration or contribution values should be explicitly described as “semi-quantitative” or “empirical estimates”.
The total particle-phase OA signal reached a maximum at 300 °C (Fig. S1a). Therefore, the authors selected 300 °C as the operating temperature for field measurements. However, maximizing the total signal does not necessarily mean that the original particle-phase molecules are measured most accurately. The continued increase in signal from above 200 °C to 300 °C may reflect more complete evaporation, but it may also arise from thermal decomposition of oligomers, peroxides, carboxylic acids, or organic nitrates, as well as dehydration, decarboxylation, and fragmentation or recombination processes. Have the authors compared the complete molecular spectra at different temperatures? The authors state that thermal decomposition cannot be fully excluded during the desorption process, but that this effect is generally considered limited under the current operating conditions. The authors should provide a more substantial justification or supporting evidence for this assertion.
Minor comments
Abstract, L30–31: an r value of 0.88 only indicates that the two signals co-vary over time; it does not demonstrate the accuracy of the absolute concentrations. Therefore, the statements that this calibration “demonstrates quantitative capability” (L30-31) and that the study provides “quantitative molecular-level characterization” (L44) are not sufficiently accurate.
L168–170: The main text reports an average evaporation efficiency of approximately 70%, whereas Sect. S1.5 reports a range of 70%–92%. Please reconcile these values. The description of particle-volume loss as direct volatilization of organic material should also be corrected.
L249–255: Please explain how the alternating 10 min sample and background periods were paired. Background interpolation during rapidly changing conditions may introduce either positive or negative biases. A representative measurement cycle and the stability of the zero-air/HEPA-filter background should be shown.
L334–339: An r2 value of 0.70 between PM1 and PM2.5 is insufficient on its own to demonstrate that “submicron particles dominated fine particulate mass.” The PM1/PM2.5 mass ratio and its distribution should be reported.
L357–360: The cross-reference to “Sect. 2.5.2” is incorrect and should be Sect. 2.4.2.
Supplement: Figure S26 is used twice. The second occurrence should be renumbered as Fig. S27.