the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 10 Mar 2026
Measurements of NaCl in ambient air with a Capture Vaporizer-ToF-ACSM
Abstract. Sea spray aerosol is important for climate and atmospheric chemistry by influencing radiative forcing and heterogeneous reactions, but few online methods exist for quantifying sub-micron sea spray concentrations. Common chemical speciation instruments, such as aerosol mass spectrometers (AMS) and aerosol chemical speciation monitors (ACSM), are usually not used for sea salt quantification due to the incomplete evaporation of refractory sodium chloride (NaCl). This study evaluates the capability of the time-of-flight-ACSM (ToF-ACSM) equipped with a capture vaporizer (CV) to detect and quantify sea salt aerosol for the first time. Key NaCl marker ions (m/z 23 (Na), m/z 58 (Na35Cl) and m/z 60 (Na37Cl) were identified through a controlled laboratory calibration. The calibration experiments show that when the ACSM response (ions/s) is normalized by the available particle surface area, the response is independent of particle concentration and only weakly dependent on particle size for monodisperse NaCl aerosol. When considering aerosol mass concentrations without normalization for the available particle surface area, it is only possible to derive ambient sea salt mass concentrations from the ACSM signal with prior information on particle size due to the observed size dependence. Furthermore, controlled chamber experiments indicated that secondary organic aerosol (SOA) formed from α-pinene as a precursor and condensed on the NaCl particles does not produce significant amounts of fragments at the m/z values characteristic for NaCl. Field experiments at a coastal site showed that conditions with onshore winds resulted in high correlations (R2 = 0.949–0.977) between the three key NaCl marker ions. By applying the laboratory-derived calibration formula to the raw CV-ToF-ACSM m/z 23 signal, sea-salt aerosol surface concentrations could be quantitatively determined in real time. However, the slope between the fragments at m/z 23 and m/z 58 is lower in the ambient data than in the laboratory calibration, suggesting reduced Cl relative to Na due to aging reactions of the sea salt particles in the coastal environment. Overall, these results demonstrate that the CV-ToF-ACSM can provide quantitative real-time information on submicron sea salt aerosol before ageing, particularly in terms of surface area, while accurate mass concentration retrieval requires additional NaCl size distribution information. These findings highlight the potential to improve the characterization of marine aerosol sources and their role in atmospheric processes.
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Status: closed (peer review stopped)
- RC1: 'Comment on ar-2026-8', Anonymous Referee #1, 11 Apr 2026
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RC2: 'Comment on ar-2026-8', Anonymous Referee #2, 22 Apr 2026
Van den Born et al. present the first systematic calibration of a CV-ToF-ACSM for the detection and quantification of sea salt aerosol, using the typical m/z 23, 58 and 60 sea salt marker ions and demonstrating that the instrument calibration response scales with particle surface area. The study provides a useful addition to the existing literature, most substantive points have already been addressed by reviewer 1, leaving limited additional issues to raise.
In Ovadnevaite et al 2012, I understand that a scaling a factor of 51 was retained for ²³Na³⁵Cl at m/z 58 as the simplest way to estimate sea salt mass concentration in µg m⁻³ which was confirmed through offline filter comparison. The authors here have eight months of near-continuous data at the Lutjewad coastal station, if offline filter measurements or ion chromatography data are available for this period, even at coarser time resolution, a similar validation would considerably strengthen the paper and is encouraged. If no such collocated filter data exist, the authors could attempt to reproduce Figure 5 from Ovadnevaite et al. (2012). Examining whether the typical power law relationship shows up between CV-ToF-ACSM sea salt m/z tracers and wind speed during stormy marine episodes would be a nice addition in the supplementary.
Given that the CV her operates at a different temperature (~550°C) and has a longer particle residence time than the standard vaporizer (~650°C used in Ovadnevaite et al. 2012), it is conceivable that the CV produces a different fragmentation pattern, potentially generating CV-specific sea salt-related ions? The sea salt family in the HR-ToF-AMS included a rich set of ions: ²³Na, Mg, ²⁵Mg, ²⁶Mg, ³⁵Cl, H³⁵Cl, ³⁷Cl, H³⁷Cl, K, ⁴¹K, Mn, Fe, Na³⁵Cl, ²⁴Mg³⁵Cl, Na³⁷Cl, ²⁶Mg³⁵Cl, ²⁵Mg³⁷Cl, ²⁶Mg³⁷Cl, ⁴⁰Ca³⁵Cl, ⁴⁰Ca³⁷Cl, Br, Na₂³⁵Cl, Na₂³⁷Cl, and several MgCl₂ isotopologues. Could the authors include one or more representative mass spectra in the supplementary material, from the laboratory calibration or ambient sampling and briefly comment on this?
Finally, the authors selected three mobility diameters of 150, 200 and 250 nm for their calibration experiment. While the use of discrete DMA-selected sizes is standard practice, the authors could briefly justify why this particular size range was chosen, and whether the derived calibration relationship is expected to hold outside the 150-250 nm range. Sea salt particles are highly hygroscopic and carry multiple charges when nebulized, inversion could potentially misassign counts from larger multiply-charged particles into the size range used for surface area calculation, biasing the normalization. Could the authors confirm that multiple charging corrections artefacts were not an issue for the sea salt calibration?
Subject to the points raised by reviewer 1 and above, the manuscript is a very useful contribution to the literature.Citation: https://doi.org/10.5194/ar-2026-8-RC2
Status: closed (peer review stopped)
-
RC1: 'Comment on ar-2026-8', Anonymous Referee #1, 11 Apr 2026
This paper describes the detection and quantification of sea salt aerosol with a TOF-ACSM equipped with a capture vaporizer. The authors performed calibration experiments with size-selected NaCl particles and used the results to analyze ambient data from two field campaigns as well as chamber data with NaCl seeds. This paper is a nice contribution to the literature and should be accepted after consideration of the following comments:
Major comments:
- The calibration experiments suggest that the response at 23, 58 and 60 is more proportional to aerosol surface area than to aerosol mass. Aerosol surface area is not commonly reported. How useful is it? Do modelers use it? I think you need some explanation for why this is an important quantity to report.
- If you apply Eq 1 to the ambient measurements for the marine air, how well does the calculated surface area agree with the surface area measured by the SMPS for that site, assuming all of the aerosol is sea salt aerosol? This would be an important confirmation of your approach.
- Do you have any marine air masses at CESAR and what slopes do you get for the 23, 58 and 60 ions?
- The ions at 35, 36, 37 and 38 are also used to quantify Cl compounds. Did you look at those ions in the calibration experiments and/or the ambient measurements? It might be interesting if there were different ratios for marine (NaCl) and continental (NH4Cl) air masses. In addition, not all CVs have signal at 58 and 60, so a fingerprint at the Cl ions would be useful.
- With the standard vaporizer, calibrations for NaCl are done with a mixture of NaCl and NH4NO3 so that the NO3 is an internal standard. Did you try that calibration technique? How well did the results agree with assuming CE=1? It seems clear from your reported size dependence that the CE is not actually 1 for NaCl particles even in the capture vaporizer.
- I am not completely clear on the point of including the AIDA data. You show that the a-pinene SOA does not have organic fragments at 23, 58 and 60 but, on the other hand, you clearly do have organic interference at 58 and 60 in the continental air masses in some seasons. In addition, for chamber experiments, you should adjust the frag table to account for the NaCl seed instead of lumping the 58 in with organics. If you want to keep the AIDA data, I would put it after the calibration and ambient data which are more important.
Minor comments:
Lines 56-58: You need another sentence or two explaining what the vaporizer is.
Line 58: Be more specific about the impact of the CV on thermal decomposition. Instead of “can alter” say “increases.”
Line 60: The difference in temperature between the SV at 600 C and the CV and 550 C has very little impact on fragmentation. It is really about the structure and residence time. I would delete the end of this sentence.
Figure 1 caption: I don’t see a purple shaded area. The org signal does not go to zero at the end. Is that 58 or something else?
Lines 197-198. I don’t see how 58 can be the most dominant ion in Org after the a-pinene injection.
Figure 2. You need some kind of legend for the different concentrations. The y-axes should be labeled with mass and surface area because it is easy to miss the change in units. Scale both y-axes from 0. I don’t understand what the /sc and /mc in the legend are referring to.
Line 221 and line 234. I don’t think these slopes are useful to report since you are not using them to calculate anything and you would need the intercepts, too. You say there’s a factor of two change for mass concentration. State what the relative change is for surface area.
Line 228. “it is impossible” seems a bit strong. The size dependence does introduce some uncertainty but one could still report concentration.
Line 235 “confirming the absence” is also a bit strong. There is a size dependence when normalized by surface area. It is just less pronounced.
Line 261 and Figure 3 legends. Do you really think you have three significant digits in R2?
Lines 296-299. This is an interesting observation. Do you see enough SO4 or NO3 to confirm? Do you see different slopes at Cabauw?
Line 343. The background signal also changes with time, even for a given instrument.
Line 347 and line 364. I don’t understand this comment about NaCl before aging. Do you think aging changes the surface area? How is what you report related to the actual aerosol?
Line 355. This claim of minimal interference is contradicted later in the paragraph. Do you mean for marine air masses?
SI line 3. “inclusion in the analysis” rather than “data acquisition”
Figure S1. Can you use different symbols for the different sizes? Those colors are very hard to tell apart. Also, “analyzed” rather than “collected” in the caption.
Figure S2. I don’t see a purple shaded area. Do you know why the organic is rising before you inject a-pinene?
Typographical/grammatical errors:
Line 74: “in” rather than “at” the samples.
Line 98: Define AIDA.
Line 122: Define CAINA.
Lines 139-141: Repeats information in lines 141-143. Delete this sentence.
Line 158: Maybe “instrument” or “sampling” rather than “sample container.”
Line 163: Insert “at” before coordinates.
Line 226: Remove the “±”
Lines 247-251. This is a long, somewhat confusing sentence. I would put a period after “Germany.” Then start the next sentence “This allowed investigation of truly marine air, although…” and get rid of the parentheses.
Line 258. List the m/z’s as y vs x and in the order shown in Fig. 3, meaning 23, 58,23, 60, 60, 58. Same thing on line286.
Line 274. I think you mean offshore (continental) rather than onshore.
Line 361. Say “lack of” rather than “missing” correlation.
SI Section 2. “held” rather than “remained”
Citation: https://doi.org/10.5194/ar-2026-8-RC1 -
RC2: 'Comment on ar-2026-8', Anonymous Referee #2, 22 Apr 2026
Van den Born et al. present the first systematic calibration of a CV-ToF-ACSM for the detection and quantification of sea salt aerosol, using the typical m/z 23, 58 and 60 sea salt marker ions and demonstrating that the instrument calibration response scales with particle surface area. The study provides a useful addition to the existing literature, most substantive points have already been addressed by reviewer 1, leaving limited additional issues to raise.
In Ovadnevaite et al 2012, I understand that a scaling a factor of 51 was retained for ²³Na³⁵Cl at m/z 58 as the simplest way to estimate sea salt mass concentration in µg m⁻³ which was confirmed through offline filter comparison. The authors here have eight months of near-continuous data at the Lutjewad coastal station, if offline filter measurements or ion chromatography data are available for this period, even at coarser time resolution, a similar validation would considerably strengthen the paper and is encouraged. If no such collocated filter data exist, the authors could attempt to reproduce Figure 5 from Ovadnevaite et al. (2012). Examining whether the typical power law relationship shows up between CV-ToF-ACSM sea salt m/z tracers and wind speed during stormy marine episodes would be a nice addition in the supplementary.
Given that the CV her operates at a different temperature (~550°C) and has a longer particle residence time than the standard vaporizer (~650°C used in Ovadnevaite et al. 2012), it is conceivable that the CV produces a different fragmentation pattern, potentially generating CV-specific sea salt-related ions? The sea salt family in the HR-ToF-AMS included a rich set of ions: ²³Na, Mg, ²⁵Mg, ²⁶Mg, ³⁵Cl, H³⁵Cl, ³⁷Cl, H³⁷Cl, K, ⁴¹K, Mn, Fe, Na³⁵Cl, ²⁴Mg³⁵Cl, Na³⁷Cl, ²⁶Mg³⁵Cl, ²⁵Mg³⁷Cl, ²⁶Mg³⁷Cl, ⁴⁰Ca³⁵Cl, ⁴⁰Ca³⁷Cl, Br, Na₂³⁵Cl, Na₂³⁷Cl, and several MgCl₂ isotopologues. Could the authors include one or more representative mass spectra in the supplementary material, from the laboratory calibration or ambient sampling and briefly comment on this?
Finally, the authors selected three mobility diameters of 150, 200 and 250 nm for their calibration experiment. While the use of discrete DMA-selected sizes is standard practice, the authors could briefly justify why this particular size range was chosen, and whether the derived calibration relationship is expected to hold outside the 150-250 nm range. Sea salt particles are highly hygroscopic and carry multiple charges when nebulized, inversion could potentially misassign counts from larger multiply-charged particles into the size range used for surface area calculation, biasing the normalization. Could the authors confirm that multiple charging corrections artefacts were not an issue for the sea salt calibration?
Subject to the points raised by reviewer 1 and above, the manuscript is a very useful contribution to the literature.Citation: https://doi.org/10.5194/ar-2026-8-RC2
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- 1
This paper describes the detection and quantification of sea salt aerosol with a TOF-ACSM equipped with a capture vaporizer. The authors performed calibration experiments with size-selected NaCl particles and used the results to analyze ambient data from two field campaigns as well as chamber data with NaCl seeds. This paper is a nice contribution to the literature and should be accepted after consideration of the following comments:
Major comments:
Minor comments:
Lines 56-58: You need another sentence or two explaining what the vaporizer is.
Line 58: Be more specific about the impact of the CV on thermal decomposition. Instead of “can alter” say “increases.”
Line 60: The difference in temperature between the SV at 600 C and the CV and 550 C has very little impact on fragmentation. It is really about the structure and residence time. I would delete the end of this sentence.
Figure 1 caption: I don’t see a purple shaded area. The org signal does not go to zero at the end. Is that 58 or something else?
Lines 197-198. I don’t see how 58 can be the most dominant ion in Org after the a-pinene injection.
Figure 2. You need some kind of legend for the different concentrations. The y-axes should be labeled with mass and surface area because it is easy to miss the change in units. Scale both y-axes from 0. I don’t understand what the /sc and /mc in the legend are referring to.
Line 221 and line 234. I don’t think these slopes are useful to report since you are not using them to calculate anything and you would need the intercepts, too. You say there’s a factor of two change for mass concentration. State what the relative change is for surface area.
Line 228. “it is impossible” seems a bit strong. The size dependence does introduce some uncertainty but one could still report concentration.
Line 235 “confirming the absence” is also a bit strong. There is a size dependence when normalized by surface area. It is just less pronounced.
Line 261 and Figure 3 legends. Do you really think you have three significant digits in R2?
Lines 296-299. This is an interesting observation. Do you see enough SO4 or NO3 to confirm? Do you see different slopes at Cabauw?
Line 343. The background signal also changes with time, even for a given instrument.
Line 347 and line 364. I don’t understand this comment about NaCl before aging. Do you think aging changes the surface area? How is what you report related to the actual aerosol?
Line 355. This claim of minimal interference is contradicted later in the paragraph. Do you mean for marine air masses?
SI line 3. “inclusion in the analysis” rather than “data acquisition”
Figure S1. Can you use different symbols for the different sizes? Those colors are very hard to tell apart. Also, “analyzed” rather than “collected” in the caption.
Figure S2. I don’t see a purple shaded area. Do you know why the organic is rising before you inject a-pinene?
Typographical/grammatical errors:
Line 74: “in” rather than “at” the samples.
Line 98: Define AIDA.
Line 122: Define CAINA.
Lines 139-141: Repeats information in lines 141-143. Delete this sentence.
Line 158: Maybe “instrument” or “sampling” rather than “sample container.”
Line 163: Insert “at” before coordinates.
Line 226: Remove the “±”
Lines 247-251. This is a long, somewhat confusing sentence. I would put a period after “Germany.” Then start the next sentence “This allowed investigation of truly marine air, although…” and get rid of the parentheses.
Line 258. List the m/z’s as y vs x and in the order shown in Fig. 3, meaning 23, 58,23, 60, 60, 58. Same thing on line286.
Line 274. I think you mean offshore (continental) rather than onshore.
Line 361. Say “lack of” rather than “missing” correlation.
SI Section 2. “held” rather than “remained”