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https://doi.org/10.5194/egusphere-2025-6310
© 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-2025-6310
© Author(s) 2026. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
12 Jan 2026
| 12 Jan 2026
Status: this preprint is open for discussion and under review for Atmospheric Chemistry and Physics (ACP).
Gas-particle partitioning, molecular weight, and yield of organic nitrate under different urban VOC, NOx, and oxidation conditions during SAPHIR-CHANEL campaign
Abstract. Oxidation of volatile organic compounds (VOCs) involving hydroxyl radicals (OH.), nitrogen oxides (NOx), or nitrate radicals (NO3.) forms organic nitrates that undergo gas-particle partitioning, changing the lifetime of nitrogen compounds and their deposition on ecosystems. In urban areas, VOC composition is complex, with contributions from traffic, cooking, volatile chemical products (VCPs), and biogenic emissions. Secondary organic aerosol (SOA) formation from urban VOC mixtures was investigated using chamber experiments during the SAPHIR-CHANEL campaign under realistic VOC-NOx and oxidation conditions. The yield of total organic nitrates is higher for precursor mixtures with a higher percentage of unsaturated VOCs, such as those from traffic and cooking sources (11–21 %), compared to VCPs and complex urban emission replicas (2–7 %). Enhanced particle-phase partitioning is observed under nighttime oxidation (by NO3.) versus daytime oxidation (by OH.). Particulate organic nitrates have a higher average molecular weight under nighttime conditions (331 ± 13 g mol-1) than under daytime conditions (258 ± 24 g mol-1) due to increased oligomerization. Similarly, the mass fraction of the total organic aerosol that is organic nitrate is 2.6–4.5 times higher under nighttime than daytime conditions, likely due to higher molecular weight and lower temperatures. Although gas-phase organic nitrate composition varies substantially between precursor mixtures, bulk organic nitrate volatility is generally similar to that of modeled oxidized monoterpene nitrates (10−4–10−2 m3 μg−1 at 18–40 °C). These findings improve understanding of bulk organic nitrate sources and properties in a complex urban environment, allowing better simulations of air quality and nitrate deposition.
How to cite. Nursanto, F. R., He, Q., van de Wouw, S., Zanders, A., Hohaus, T., Kroese, W. S. J., Wegener, R., Adam, M. G., Winter, B., Dubus, R., Kesper, L., Rohrer, F., Wang, Y., Matthews, E., Voliotis, A., Bannan, T. J., McFiggans, G., Coe, H., Wu, Y., Roska, M., Canagaratna, M., Alton, M., Coggon, M. M., Stockwell, C. E., Bates, K. H., Pfannerstill, E. Y., Zorn, S. R., Wang, H., Riva, M., Perrier, S., Yang, B., Liu, L., Novelli, A., Färber, M., Fuchs, H., Marcillo Lara, A. C., Grasse, A., Wesolek, C., Tillmann, R., Holzinger, R., Krol, M. C., Gkatzelis, G. I., and Fry, J. L.: Gas-particle partitioning, molecular weight, and yield of organic nitrate under different urban VOC, NOx, and oxidation conditions during SAPHIR-CHANEL campaign, EGUsphere [preprint], https://doi.org/10.5194/egusphere-2025-6310, 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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Farhan R. Nursanto
CORRESPONDING AUTHOR
Department of Environmental Sciences, Wageningen University, 6708 PB Wageningen, Netherlands
Quanfu He
Institute of Climate and Energy Systems, ICE-3: Troposphere, Forschungszentrum Jülich, Jülich, 52428, Germany
now at: Earth, Ocean and Atmospheric Sciences Thrust, Function Hub, The Hong Kong University of Science and Technology (Guangzhou), Guangzhou, 511453, China
Sophia van de Wouw
Department of Environmental Sciences, Wageningen University, 6708 PB Wageningen, Netherlands
Annika Zanders
Institute of Climate and Energy Systems, ICE-3: Troposphere, Forschungszentrum Jülich, Jülich, 52428, Germany
Thorsten Hohaus
Institute of Climate and Energy Systems, ICE-3: Troposphere, Forschungszentrum Jülich, Jülich, 52428, Germany
Willem S. J. Kroese
Department of Physics, Institute for Marine and Atmospheric Research Utrecht, Utrecht University, Princetonplein 5, 3584CC, Utrecht, Netherlands
Robert Wegener
Institute of Climate and Energy Systems, ICE-3: Troposphere, Forschungszentrum Jülich, Jülich, 52428, Germany
Max Gerrit Adam
Institute of Climate and Energy Systems, ICE-3: Troposphere, Forschungszentrum Jülich, Jülich, 52428, Germany
Benjamin Winter
Institute of Climate and Energy Systems, ICE-3: Troposphere, Forschungszentrum Jülich, Jülich, 52428, Germany
René Dubus
Institute of Climate and Energy Systems, ICE-3: Troposphere, Forschungszentrum Jülich, Jülich, 52428, Germany
Lukas Kesper
Institute of Climate and Energy Systems, ICE-3: Troposphere, Forschungszentrum Jülich, Jülich, 52428, Germany
Franz Rohrer
Institute of Climate and Energy Systems, ICE-3: Troposphere, Forschungszentrum Jülich, Jülich, 52428, Germany
Yuwei Wang
Department of Earth and Environmental Sciences, Centre for Atmospheric Science, University of Manchester, Manchester M13 9PL, United Kingdom
Emily Matthews
Department of Earth and Environmental Sciences, Centre for Atmospheric Science, University of Manchester, Manchester M13 9PL, United Kingdom
Aristeidis Voliotis
Department of Earth and Environmental Sciences, Centre for Atmospheric Science, University of Manchester, Manchester M13 9PL, United Kingdom
National Centre for Atmospheric Science, University of Manchester, Manchester M13 9PL, United Kingdom
Thomas J. Bannan
Department of Earth and Environmental Sciences, Centre for Atmospheric Science, University of Manchester, Manchester M13 9PL, United Kingdom
Gordon McFiggans
Department of Earth and Environmental Sciences, Centre for Atmospheric Science, University of Manchester, Manchester M13 9PL, United Kingdom
Department of Earth and Environmental Sciences, Centre for Atmospheric Science, University of Manchester, Manchester M13 9PL, United Kingdom
National Centre for Atmospheric Science, University of Manchester, Manchester M13 9PL, United Kingdom
Yizhen Wu
Institute of Climate and Energy Systems, ICE-3: Troposphere, Forschungszentrum Jülich, Jülich, 52428, Germany
Milan Roska
Institute of Climate and Energy Systems, ICE-3: Troposphere, Forschungszentrum Jülich, Jülich, 52428, Germany
Manjula Canagaratna
Aerodyne Research Inc., Billerica, Massachusetts 01821, USA
Mitch Alton
Aerodyne Research Inc., Billerica, Massachusetts 01821, USA
Matthew M. Coggon
Chemical Sciences Laboratory, National Oceanic and Atmospheric Administration, Boulder, CO, 80305, USA
Chelsea E. Stockwell
Chemical Sciences Laboratory, National Oceanic and Atmospheric Administration, Boulder, CO, 80305, USA
Kelvin H. Bates
Chemical Sciences Laboratory, National Oceanic and Atmospheric Administration, Boulder, CO, 80305, USA
Department of Mechanical Engineering, University of Colorado, Boulder, CO, 80305, USA
Eva Y. Pfannerstill
Institute of Climate and Energy Systems, ICE-3: Troposphere, Forschungszentrum Jülich, Jülich, 52428, Germany
Institute of Geophysics and Meteorology, University of Cologne, Cologne, 50969, Germany
Sören R. Zorn
Institute of Climate and Energy Systems, ICE-3: Troposphere, Forschungszentrum Jülich, Jülich, 52428, Germany
Institute of Climate and Energy Systems, ICE-3: Troposphere, Forschungszentrum Jülich, Jülich, 52428, Germany
Matthieu Riva
Université Claude Bernard Lyon 1 CNRS, IRCELYON 69626, Villeurbanne, France
Sebastien Perrier
Université Claude Bernard Lyon 1 CNRS, IRCELYON 69626, Villeurbanne, France
Boxing Yang
PSI Center for Energy and Environmental Sciences, Paul Scherrer Institute, Villigen, Switzerland
PSI Center for Energy and Environmental Sciences, Paul Scherrer Institute, Villigen, Switzerland
Anna Novelli
Institute of Climate and Energy Systems, ICE-3: Troposphere, Forschungszentrum Jülich, Jülich, 52428, Germany
Michelle Färber
Institute of Climate and Energy Systems, ICE-3: Troposphere, Forschungszentrum Jülich, Jülich, 52428, Germany
Hendrik Fuchs
Institute of Climate and Energy Systems, ICE-3: Troposphere, Forschungszentrum Jülich, Jülich, 52428, Germany
Department of Physics, University of Cologne, Cologne, 50923, Germany
Andrea Carolina Marcillo Lara
Institute of Climate and Energy Systems, ICE-3: Troposphere, Forschungszentrum Jülich, Jülich, 52428, Germany
Achim Grasse
Institute of Climate and Energy Systems, ICE-3: Troposphere, Forschungszentrum Jülich, Jülich, 52428, Germany
Christian Wesolek
Institute of Climate and Energy Systems, ICE-3: Troposphere, Forschungszentrum Jülich, Jülich, 52428, Germany
Ralf Tillmann
Institute of Climate and Energy Systems, ICE-3: Troposphere, Forschungszentrum Jülich, Jülich, 52428, Germany
Rupert Holzinger
Department of Physics, Institute for Marine and Atmospheric Research Utrecht, Utrecht University, Princetonplein 5, 3584CC, Utrecht, Netherlands
Maarten C. Krol
Department of Environmental Sciences, Wageningen University, 6708 PB Wageningen, Netherlands
Department of Physics, Institute for Marine and Atmospheric Research Utrecht, Utrecht University, Princetonplein 5, 3584CC, Utrecht, Netherlands
Georgios I. Gkatzelis
Institute of Climate and Energy Systems, ICE-3: Troposphere, Forschungszentrum Jülich, Jülich, 52428, Germany
Department of Environmental Sciences, Wageningen University, 6708 PB Wageningen, Netherlands
Short summary
Urban air contains reactive gases that can form organic nitrate particles and carry nitrogen oxides pollution far from cities. We recreated urban emissions in a large atmospheric chamber and observed their reactions under day and night conditions. We found that these emissions form organic nitrate particles similar to those from natural sources, with higher amounts and heavier particles at night, making nitrogen pollution longer lived and likely to travel further before depositing on ecosystems.
Urban air contains reactive gases that can form organic nitrate particles and carry nitrogen...
This manuscript reports a set of SAPHIR-CHANEL chamber experiments and investigated the bulk organic nitrate formation, molar yield, and partitioning. A range of biogenic and urban VOC-NOx mixtures under daytime and nighttime conditions were investigated. The day-night differences was interpreted using a combination of online mass spectrometers. Overall, this study is well designed and the paper provided comprehensive analysis to support their conclusion. However, there are still some places I feel the authors can improve and need some additional clarifications. Therefore, I suggest a minor revision.
Major comments:
1. The day-night interpretation considered both temperature/RH difference and chemical composition change. The impact from two major causes were not separated.
The discussion mentioned that lower temperature and higher RH in nighttime experiments enhanced partitioning, thus increasing Cp/Cg. At the same time, more dimers were identified at nighttime samples, implying composition changes. While these two could both be true, it would be better if the impact from temperature/RH could be separated with that from chemical composition/oxidation regime. More discussion about the differences in chemical composition between daytime and nighttime experiments with comparable temperature condition would be helpful.
2. Temperature effects should be quantified (e.g. Clausius-Clapeyron equation), while currently temperature is used as a post-hoc explanation rather than a tested hypothesis.
Given that Kp is temperature dependent and Fig. 6 explicitly plot Kp,ON versus T, a straightforward expectation is to apply a Clausius-Clapeyron correction/sensitivity analysis to test whether the observed day-night offsets are consistent with thermodynamics alone.
3. The impact of RH is mentioned together with temperature, but no mechanistic explanation is provided (i.e. water uptake, aqueous chemistry)
More discussion about how does RH impact partitioning would be helpful. Either through higher aerosol liquid water increases absorptive capacity or potential aqueous phase/heterogeneous chemistry leads to dimer formation.
4. Photochemical condition (i.e. solar flux, J-values) are not provided. Day-night conditions differ majorly in chemical reaction pathway, especially the radical production pathway. It would be helpful for this manuscript to provide photolysis metrics (e.g. solar flux), as it is an important experimental parameter when interpreting daytime oxidation.
5. The manuscript attributes the higher nighttime limonene Kp,ON to enhanced dimer formation. However, the SIMPOL-based comparison in fig.6 did not include any monoterpene dimer candidates, and the nighttime limonene SOA fall into the range of limonene monomer. Representative monoterpene dimer candidates should be included in fig.6. In addition, a structure-independent volatility estimation for the assigned molecular formulas (e.g., formula-based C*/2D VBS mapping) could provide more information of whether the nighttime experiments formed lower volatile compounds.
6. A major limitation of current analysis is that several critical metrics are not quantifiable. While the manuscript presented a rich dataset, most measurements used to infer VOC consumption, ON yield, and average molecular weight are signal based proxy without species-dependent sensitivity, fragmentation, and matrix effect. It would be helpful is the authors provide what standards were the CIMS calibrated. If any of the VOC precursors were used as calibrants, it would be helpful to better quantify the VOC consumption. Otherwise, including the uncertainty propagation from delta VOC and average molecular weight would be helpful.
Minor comments:
1. Method section: how was the chamber conditioned/cleaned between experiments?
2. line108: what are the results for background experiments and how did they help with the experiments with VOC injection?
3. line 249-251: as the author noted, other organic nitrogen compounds might be included, I wonder if other parameter can help exclude non-ON species? Such as N:O, DBE, etc.
4. line 297: what activity coefficient (or assumptions) is used in the calculation?
5. line303: what is the criteria used to determine the “SOA concentration remains stable”? Please provide more statistical information (e.g., slope threshold, standard deviation).
6. figure3: considering include RH information together with temperature, and include uncertainty/error bars for temperature and RH. For the legend, there is a overbar for carbon number = 10 and 20, please clarify what these denote.
7. line 371-372: “this could also be caused by …… in complex urban mixtures” this sentence does not seem to explain the previous conclusions, where more ON were formed for nighttime experiments, as both daytime and nighttime experiments have different VOC precursors. Please revise for clarity and logical connection.
8. line 401: what does “larger” here mean? Higher MW or higher yield? Please specify.
9. line 443-456: here the author separate all experiments into two categories, where the first one include limonene, VCP, city mixed with biogenic emission, and the second mainly include traffic and cooking emissions. The first category tends to form more dimers under nighttime conditions, while the second category tends to form high-volatility compounds. In line 461, the author draw the conclusion that BVOCs have a large impact on ON species. However, the VCP and LA anthropogenic emissions do not include BVOCs. Please refine this section.
10. line 470-471: “similarly to the trend of …… chemical species to the particle phase”. This sentence is grammatically incomplete with no main clause. Please revise for clarity.
11. figure S1: consider including time series for all the experiments and including RH for them.