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https://doi.org/10.5194/egusphere-2026-4542
© Author(s) 2026. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/egusphere-2026-4542
© Author(s) 2026. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
16 Sep 2026
| 16 Sep 2026
Status: this preprint is open for discussion and under review for Atmospheric Chemistry and Physics (ACP).
Acid-base chemistry controls the thermal desorption of vapors from inorganic and organic nanoparticles
Abstract. Here, we present measurements of inorganic and organic particles using a novel instrument that simultaneously measures both acid and base compounds via temperature-programmed desorption: a Filter Inlet for Gases and AEROsols (FIGAERO) combined with a Bipolar Time-of-Flight (BTOF) mass spectrometer. We measured particles from three different sources: atomized salt solutions, aerosols formed in the CERN CLOUD chamber, and ambient aerosols from a site in New York. We find that acids and bases do not desorb at temperatures characteristic of the volatilities of their pure compounds, but rather they desorb at higher temperatures that depend on particle composition related to the entropy of the ionic condensed state, i.e. the lattice energy. For monoprotic acids, the desorption is rate-limited by a proton transfer reaction, evidenced by simultaneous desorption of the neutral acid-base pair. For ammonium sulfate ((NH4)2SO4), we observe a step-wise release of ammonia and increase of the sulfate-to-ammonia ratio: first to triammonium sulfate hydrogen sulfate ((NH4)3H(SO4)2; letovicite), and then to ammonium hydrogen sulfate ((NH4)HSO4)). We find that organic acids and alkyl organosulfates also desorb at temperatures higher than those expected for their pure compounds, indicating reactive uptake. This suggests that a large fraction of organic compounds in particles may be light, ionic species, rather than fragments of low-volatility oligomers. Our studies show that the FIGAERO-BTOF is a highly sensitive and versatile instrument for elucidating condensed-phase aerosol chemistry.
How to cite. DeVivo, J., Stinchfield, A., Bhattacharyya, N., Alton, M., Wang, M., Schobesberger, S., Hao, L., Rogers, M., Vogel, A., Zgheib, I., Burton, N., Lietzke, C., Russell, D. M., Sommer, E., Gentner, D., Heikkinen, L., Volkamer, R., Kirkby, J., Lopez-Hilfiker, F., Worsnop, D., Canagaratna, M., and Donahue, N. M.: Acid-base chemistry controls the thermal desorption of vapors from inorganic and organic nanoparticles, EGUsphere [preprint], https://doi.org/10.5194/egusphere-2026-4542, 2026.
Competing interests: At least one of the (co-)authors is a member of the editorial board of Atmospheric Chemistry and Physics.
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Latest update: 26 Oct 2026
Jenna DeVivo
Department of Chemistry, Carnegie Mellon University, Pittsburgh, PA, United States
Center for Atmospheric Particle Studies, Carnegie Mellon University, Pittsburgh, PA, United States
Alexandria Stinchfield
Center for Atmospheric Particle Studies, Carnegie Mellon University, Pittsburgh, PA, United States
Department of Chemical Engineering, Carnegie Mellon University, Pittsburgh, PA, United States
Nirvan Bhattacharyya
Center for Atmospheric Particle Studies, Carnegie Mellon University, Pittsburgh, PA, United States
Institute for Atmospheric and Environmental Sciences, Goethe University Frankfurt, Frankfurt am Main, Hesse, Germany
Mitch Alton
Center for Aerosol and Cloud Chemistry, Aerodyne Research Inc., Billerica, Massachusetts 01821, United States
Mingyi Wang
Department of the Geophysical Sciences, University of Chicago, Chicago, IL, United States
Siegfried Schobesberger
Department of Technical Physics, University of Eastern Finland, PO Box 1627, 70211 Kuopio, Finland
Department of Chemistry, University of Colorado Boulder, Boulder, CO, 80309, United States
Cooperative Institute for Research in Environmental Sciences, Boulder, CO, 80309, United States
Liqing Hao
Department of Technical Physics, University of Eastern Finland, PO Box 1627, 70211 Kuopio, Finland
Mitchell Rogers
Department of Chemical and Environmental Engineering, Yale University, New Haven, CT, United States
Alexander Vogel
Institute for Atmospheric and Environmental Sciences, Goethe University Frankfurt, Frankfurt am Main, Hesse, Germany
Imad Zgheib
Tofwerk AG, 3645 Thun, Switzerland
Natalie Burton
Center for Atmospheric Particle Studies, Carnegie Mellon University, Pittsburgh, PA, United States
Department of Chemical Engineering, Carnegie Mellon University, Pittsburgh, PA, United States
Clara Lietzke
Department of Chemistry, University of Colorado Boulder, Boulder, CO, 80309, United States
Cooperative Institute for Research in Environmental Sciences, Boulder, CO, 80309, United States
Douglas M. Russell
Institute for Atmospheric and Environmental Sciences, Goethe University Frankfurt, Frankfurt am Main, Hesse, Germany
Eva Sommer
CERN, European Organization for Nuclear Research, 1211 Geneva, Switzerland
Faculty of Physics, University of Vienna, Strudlhofgasse 4, 1090 Vienna, Austria
Drew Gentner
Department of Chemical and Environmental Engineering, Yale University, New Haven, CT, United States
Liine Heikkinen
Department of Environmental Science and Bolin Centre for Climate Research, Stockholm University, Stockholm, Sweden
Rainer Volkamer
Department of Chemistry, University of Colorado Boulder, Boulder, CO, 80309, United States
Cooperative Institute for Research in Environmental Sciences, Boulder, CO, 80309, United States
Jasper Kirkby
Institute for Atmospheric and Environmental Sciences, Goethe University Frankfurt, Frankfurt am Main, Hesse, Germany
CERN, European Organization for Nuclear Research, 1211 Geneva, Switzerland
Felipe Lopez-Hilfiker
Tofwerk AG, 3645 Thun, Switzerland
Department of Atmospheric and Climate Science, University of Washington, Seattle, 98195 WA, United States
Douglas Worsnop
Center for Aerosol and Cloud Chemistry, Aerodyne Research Inc., Billerica, Massachusetts 01821, United States
Institute for Atmospheric and Earth System Research/Physics, University of Helsinki, Helsinki, Finland
Manjula Canagaratna
Center for Aerosol and Cloud Chemistry, Aerodyne Research Inc., Billerica, Massachusetts 01821, United States
Department of Chemistry, Carnegie Mellon University, Pittsburgh, PA, United States
Center for Atmospheric Particle Studies, Carnegie Mellon University, Pittsburgh, PA, United States
Department of Chemical Engineering, Carnegie Mellon University, Pittsburgh, PA, United States
Short summary
The vapors driving atmospheric new particle formation are uncertain, in part because of instrumental limitations at small particle sizes. This study presents a novel coupling of a temperature-programmed desorption inlet with a bipolar mass spectrometer that has multiple types of chemical ionization used to study acid-base reactions controlling particulate evaporation.This method measures more components in atmospheric aerosol and separates reactive pathways contributing to early particle growth.
The vapors driving atmospheric new particle formation are uncertain, in part because of...
Jenna de Vivo and co-authors have used temperature-programmed desorption, combined with a bipolar mass spectrometer, to study the composition of a variety of aerosol particles in both field and laboratory conditions. The main novelty of the study is the bipolar charging, which allows the simultaneous characterisation of both acidic and basic aerosol constituents. The data presented in the manuscript are hugely interesting and valuable, and the manuscript is in general fairly well written and easy to follow. I’m thus happy to recommend publication subject to some relatively minor revisions, mainly related to some phrasing, notation, and what appears (with all due respect) to be insufficient proofreading by the numerous chemists in the author list. See below for a detailed list of minor issues I found.
-The authors frame their discussion of the acid(gas) + base(gas) <=> salt(condensed phase) condensation/evaporation reactions in terms of “reactive” uptake (and its reverse). This is of course technically correct - proton transfer IS a chemical reaction. However, in contrast to most other chemical reactions (e.g. condensed-phase accretion reactions, or the reverse fragmentation reactions), acid-base reactions are typically kinetically very fast, i.e. they usually do not have substantial transition states (and even when they do, the protons often just tunnel through these). Or in other words, acids and bases are usually in equilibrium with their corresponding salts. Given this, the authors’ repeated use of the phrase “out of equilibrium” (and other similar phrases, including "rate-limiting") seems surprising and odd (see for example the second-last sentence of the whole manuscript). We can write the whole reaction sequence as HA(gas) + B(gas) <=> A(particle) + B(particle) <=> A-(particle) + HB+(particle), which covers both solid and liquid particles. When the authors state that organics are “out of equilibrium with the gas phase”, they presumably mean that the total particle-phase concentration of the acid HA (i.e. [HA(particle)] + [A-(particle)]) compared to [HA(gas)] is much larger than what we would predict if we only used the equilibrium constant (partitioning coefficient / Henry’s law coefficient / equilibrium coefficient) of the first reaction. This is true… but is it really appropriate to refer to this as a non-equilibrium or out-of-equilibrium effect - isn't it rather jjust a reflection of the fact that the equilibrium is affected by more than one reaction? (This is fully analogous to e.g. the gas-water equilibrium partitioning of an acid gas like CO2 - the deprotonation shifts the equilibrium further toward the liquid phase, in suitable pH conditions quite substantially, but it does not cease to be an equilibrium just because there are multiple reactions involved). The distinction is not just semantic - a genuine “non-equilibrium” situation implies there are some kinetic (time-dependent) aspects involved - which would probably call into question the methods used here, as the temperature ramps are taken on a timescale of tens to hundreds of seconds. A variant of this criticism applies to calling various steps "rate-limiting". While not technically wrong (if the first step in a sequence A => B => C has an equilibrium very strongly on the side of A, it may indeed be the rate-limiting step of the A => C conversion), this also implies a time-dependent kinetic framework which is not really what is going on here. Please rephrase the discussion accordingly.
-The novelty of the results concerning the inorganic acids (at least, or in particular, H2SO4) is overstated. It is very well known that sulfuric acid is a key driver of both nucleation and particle growth not (or not just) because of its low volatility, but because of its strong acidity. Indeed, the crucial role of the acidity of H2SO4 for particle formation has been known for over a century, and arguably suspected for over two centuries - see for example the excellent historical review by Malila (https://b.tellusjournals.se/articles/10.1080/16000889.2018.1471913). Even the saturation vapour pressure results from 1997 quoted in this very manuscript clearly demonstrate that pure H2SO4 does not have a particularly low volatility - so why do the authors claim (e.g. at the start of section 3, around line 143) that this is somehow “often assumed”, or that acid-base salt formation or clustering (involving at least strong inorganic acids) in an aerosol context is somehow a novel or surprising result? I would recommend going through the manuscript carefully, and toning down some of the claims concerning novelty or surprise. (Note: in contrast to the H2SO4-related results, where the authors basically just confirm what we already knew, but with a new instrument, the results on especially the smaller ORGANIC acids are new and also rather surprising, so I’m not trying to downplay the overall novelty of the results - just arguing that the authors should focus their arguments a bit better).
-As a small caveat to my point above, the comparison between ammonium nitrate and dimethylaminium nitrate is interesting. Cluster stability calculations (e.g. https://pubs.rsc.org/em/article/26/11/2036/849385 and https://acp.copernicus.org/articles/21/11637/2021/) indicate that HNO3-DMA clusters should be stabler than HNO3-NH3 clusters (at least up to a size of four acids & four bases), albeit with a much smaller difference than between H2SO4-DMA and H2SO4-NH3. Could the seeming discrepancy between this prediction and the observed thermal desorption be caused by size effects (i.e. the stability order reverses for some larger cluster size), or by humidity (which the former linked study indicates should stabilise the HNO3-NH3 clusters more)? (The authors don’t necessarily need to add speculation on this if they feel it’s outside the scope of the manuscript, I just wanted to bring the issue to their attention since it intrigued me.)
-While I accept and appreciate the overall argument presented in section 4.2, it is a bit difficult to follow in detail. What exactly are the data points whose correlation (or not) is being discussed here? If my interpretation is correct, the authors basically have three Tmax values (ammonium nitrate, ammonium hydrogen sulfate & ammonium sulfate), and then they look for a correlation between these and the corresponding enthalpy, entropy or pKa values (and find none). This is then contrasted with the generally good correlation between Tmax and vaporisation enthalpy for a larger range of (mainly organic, neither strongly acidic nor basic) substances (e.g. PEGs). Are three data points really sufficient to meaningfully discuss “correlation”? I understand the idea that if Tmax followed solely from delta-H (or pKa), then the ordering of ammonium nitrate and ammonium hydrogen sulfate Tmax values should be the opposite - and this is a valid argument - I’m just questioning whether the statistical concept of “correlation” is meaningfully applicable here.
-Please use consistent chemical terminology, and avoid using multiple different names for the same species. In particular, HSO4- should be called either “hydrogen sulfate” or “bisulfate”, not a mixture of the two terms (IUPAC recommends the former, and indeed this is the more frequently used term in the manuscript.) Right now the two different names for the same species are used even in consecutive sentences, as on lines 130-132, where the phrasing actually strongly implies that “ammonium hydrogen sulfate” and “ammonium bisulfate” would be different things (they are NOT, as I’m sure the authors actually do know). “Sulfate acid” on line 132 should similarly be just “sulfuric acid”. Also later on, “bisulfite” should probably be called “hydrogen sulfite” to comply with IUPAC recommendations.
-Table 1 and the associated discussion also has several notation issues. First, the “Acid formula” label for the 2nd column in the table is simply incorrect: the formulas given are those of the conjugate BASE anions (I note that the charge is also missing from the formula). Either add the missing H so that the formula actually matches that of the acid, or change the column name to “conjugate base formula” and add the minus. Also, in the discussion below Table 1, the connection between the chemical names in table 1 (the sodium salts), and the corresponding acids, is not very clear: e.g. the “hydroxymethanesulfonic acid” is the conjugate acid of the “formaldehyde bisulfite” anion in the first row of Table 1, but this connection is not spelled out in any way. Please make sure that the discussion connects to the table (and overall please do a “chemistry proofreading” of the manuscript - it’s annoying to have an otherwise excellent presentation marred by minor notation issues like this).
-The claim on line 24 that partitioning theory and frameworks such as the VBSare suitable for predicting how U/ELVOCs drive nucleation seems a bit exaggerated and/or premature, and possibly even in contradiction with the results in this very manuscript (which show that for many key species, the pure-compound vapour pressure has very little to do with the effective volatility). While low volatility certainly seems to be a necessary requirement for pure organic nucleation, it may be far from sufficient (especially given that we don’t actually really know the true volatilities of the most complex multifunctional species). Partitioning & VBS are on much more solid ground when it comes to (even initial) particle growth, as evidenced by observed condensation behaviour, so perhaps focus on this aspect in the argument, and leave out nucleation (or acknowledge the substantial caveats surrounding the topic).
-On line 532, “stable electrostatic network of hydrogen bonds” doesn’t really mean anything - please also note that the central claims of the cited Zhang et al study 2026 have been strongly disputed (see https://egusphere.copernicus.org/preprints/2026/egusphere-2026-3785/ and the corresponding online discussion, where all reviewers and community commenters apart from Zhang himself strongly support the presented criticism). In any case, please rephrase this sentence. (Also, I would note that the results presented here might possibly help explain the discrepancy between Zhang et al’s observations - which likely originate from larger particles, at least around 10 nm - and the well-established instability of small nanometer-sized clusters of small organics including mono- and even dicarboxylics. Might it be that the larger particles have sufficient NH3 to cause the small organic acids to deprotonate?)