Accurate measurements of organic peroxy radicals (RO₂) are critical to understanding the formation of secondary pollutants, as the loss rate of RO2 radicals determines the rate and fraction of ozone (O3) and particulate matter formed. Due to their large structural variability and low concentrations in the troposphere, the measurement of RO2 radicals in ambient air is challenging, with most techniques relying on conversion to other species before detection.
In the summer of 2022, a series of experiments covering a wide range of chemical conditions were carried out in the SAPHIR atmospheric simulation chamber at Forschungszentrum Jülich. The experiments focused on the oxidation of biogenic and anthropogenic precursors at current and future nitrogen oxides levels (from a few ppb to a few ppt of nitric oxide), using different oxidants such as hydroxyl radical (OH), O3, and nitrate radicals (NO3), covering daytime and nighttime conditions. One experiment was conducted by flushing the chamber with ambient air. Three different techniques were compared: PEroxy Radical Chemical Amplification (PERCA, three research groups), Laser Induced Fluorescence (LIF, three research groups) and Chemical Ionization Mass Spectrometry (CIMS, one research group).
Overall, good agreement (within the stated accuracy of each instrument) was found for most of the conditions investigated, with deviations observed for one PERCA instruments for high temperatures and acyl peroxyl nitrates (APNs) concentrations. The results highlight the strengths and limitations of each measurement method in terms of sensitivity, accuracy, temporal resolution and potential interferences from other species.
How to cite: Novelli, A., Chen, W., Dusanter, S., Fittschen, C., Andrés Hernández, M. D., Dagmar, K., Schoemaecker, C., Whalley, L., Zhao, W., and Fuchs, H. and the ROxCOMP team: Comparison of ROx radicals measurements in the atmospheric simulation chamber SAPHIR, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17557, https://doi.org/10.5194/egusphere-egu25-17557, 2025.
Organic peroxy radicals (RO2) are key species in the troposphere as their chemistry leads to the formation of secondary organic aerosols and ozone. RO2 radicals mainly react with nitric oxide (NO) in the lower troposphere, leading to either (i) radical propagation, which sustains the atmospheric oxidation capacity, or (ii) the formation of organic nitrates (RONO2), where both RO2 and NO2 are sequestered, thus reducing radical propagation rates and the formation of secondary pollutants. The latter pathway exhibits RONO2 yields ranging from negligible up to 35%, depending on the RO2 molecular structure.
We propose a new approach to quantify RONO2 yields from RO2+NO reactions, taking advantage of the measurement principle of chemical amplifiers (CA), initially developed for measuring ambient concentrations of ROx radicals (OH, HO2 and RO2). We will show that the CA can be used as a kinetic apparatus to quantify an “integrated” RONO2 yield for chemical systems where a specific volatile organic compound (VOC) is oxidized by OH. In this presentation, we will discuss applications for the following chemical systems: ethane+OH, cyclohexane+OH and isoprene+OH, emphazing how the determinations contrast to published data. Both advantages and drawbacks will be highlighted for this new approach.
How to cite: Strunz, C., Tomas, A., Noziere, B., and Dusanter, S.: Development of a new approach to quantify organic nitrate yields from RO2+NO reactions – Application to ethane-, cyclohexane- and isoprene-derived RO2 radicals, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9743, https://doi.org/10.5194/egusphere-egu25-9743, 2025.
Organic peroxy radicals (ROO•) are critical intermediates in atmospheric chemistry, yet their interactions with solid surfaces remain poorly understood due to challenges in monitoring these reactive species. We present a new experimental flow tube setup designed to overcome these limitations, enabling direct measurement of the uptake of ROO• on solid surfaces.
In our approach, ROO• (specifically CH3OO• and 1-C3H7OO•) are generated photolytically and introduced into reaction tubes composed of, or filled with, various materials. The system is coupled with a Proton-Transfer-Reaction Time-of-Flight Mass Spectrometer (PTR-TOF-MS), allowing direct detection of ROO•. Reaction kinetics are determined by varying the residence time in the reactor tube, achieved either by adjusting the tube length or changing the gas flow rate.
Using this method, we successfully monitored the uptake of CH3OO• and 1-C3H7OO• on solid surfaces and identified reaction products. Results shown that the ROO• uptake is highly dependent on the surface material. Non-conductive materials such as borosilicate glass and perfluoroalkoxy alkane (PFA) showed negligible uptake, whereas metallic surfaces exhibited significant reactivity. A second study examined atmospherically relevant inorganic salts.
Our findings highlight the pivotal role of material redox properties in driving the surface reactivity of organic peroxy radicals, providing new insights into their fundamental behavior and raising new questions about their role in atmospheric environments.
How to cite: Durif, O. and Nozière, B.: A Novel Flow Tube Method for Measuring Gas-Phase Reactions Kinetics and Uptake on Solid Surfaces: Application to Organic Peroxy Radical, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11187, https://doi.org/10.5194/egusphere-egu25-11187, 2025.
Peroxy radicals (RO2) play a central role in the atmospheric degradation of volatile organic compounds (VOC) whose atmospheric lifetime and further reactions depend strongly on the prevailing conditions. In air masses influenced by anthropogenic activities the fate of a peroxy radical is typically dominated by its reaction with NO which finally results in the formation of tropospheric ozone. Once NO no longer dominates, peroxy radical chemistry becomes more complex and includes reactions with HO2, other peroxy radicals or unimolecular isomerization (H shift). The last can occur multiple times, each shift being followed by progressive addition of O2. The resultant highly oxidized peroxy radicals either decompose or undergo bimolecular reactions. This process causes rapid formation of low-volatility vapours that contribute to new particle formation.
Apart from the progress made over the last decade in understanding peroxy radical chemistry and the formation of highly oxidized species in particular, the formation mechanisms and the influence of the peroxy radical structure on the reactivity are still not well-established. The detection of highly oxygenated organic molecules (HOM) was achieved by chemical ionisation mass spectrometry which provides only information on the chemical formula. Further, oxidation experiments on biogenic VOC (terpenes etc.) result in a complex mixture of peroxy radicals impeding to gain detailed information on formation mechanisms.
To address existing analytical and experimental shortcomings in characterizing the formation and fate of peroxy radicals, three iodo-carbonyl precursors (i.e., C7H13OI) were synthesized to produce specific peroxy radicals via photolysis. The experiments were performed in the QUAREC atmospheric simulation chamber (University of Wuppertal). The model reaction systems were monitored by Fourier-Transform infrared (FTIR) spectroscopy and molecular characterization of the resulting oxidation products was retrieved using the low pressure IMS-Tof-CIMS. The experimental set-up was carefully adjusted to differentiate between autoxidation processes, permutation reactions, and the reaction of peroxy radicals with HO2. The influence of the peroxy radical structure on the reactivity will be discussed.
How to cite: Illmann, N., Zgheib, I., Fache, F., Patroescu-Klotz, I., Lopez, F., Graf, S., Gerber, S., Kamrath, M., and Riva, M.: Investigations on the fate of selected peroxy radicals using synthetized precursors and isomeric speciation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12982, https://doi.org/10.5194/egusphere-egu25-12982, 2025.
Biomass burning (BB) represents a global concern due to its impact on air pollution, health and climate change, resulting in 2.3 million premature deaths yearly. BB in the residential sector is one of the main sources of primary Particulate Matter emissions. BB emits a significant amount of black and brown carbon, Polycyclic Aromatic Hydrocarbons, and contributes to secondary formation of ozone by photochemical reaction of volatile organic compounds and nitrogen oxides. On the other side, BB is a green and renewable alternative source to fossil fuels reducing carbon dioxide emissions with lower costs, whose use is even expanded due to the last energy crisis and natural gas cost, increasing its impact on both rural and urban areas.
Significantly, BB emission factors (EFs) are affected by a wide range of uncertainties, in terms of primary and secondary air pollutants contribution and in term of health impact estimates. Comprehensive chemical characterization of primary and secondary emissions, combined with the understanding of its potential health effects, requires dedicated experiments to assess a proper offset of BB.
During the MIND-BB campaign primary gaseous and particulate BB emissions from domestic heating devices were sampled and measured within the outdoor EUPHORE chamber, monitoring chemical and physical properties. EUPHORE, sited at CEAM (Valencia-ES), is highly instrumentalized and adapted to introduce fumes from domestic stoves. Given its large size and thanks to its Teflon® FEP cover and to the possibility of opening and closing its sun barrier, the facility can simulate near-real conditions, under both sunlight and night situations. EUPHORE allowed the analysis as well as the aging of the primary emissions. In parallel, we exposed A549 lung epithelial cells cultured at the air-liquid-interface (ALI) to the primary and secondary emissions to evaluate their toxicological hazard mimicking human exposure conditions. Two types of stoves, fuelled with pellet or wood-logs, were tested, and the latter with two different types of wood: Pine and Oak. Measures were performed on primary emissions and aged compounds for each type of fuel (certified pellet, pine, oak), under different conditions (daylight and night) and operation phases (flaming, smouldering). Moreover, for the first time in an outdoor simulation chamber, we performed the direct ALI exposure of human lung cells to primary and aged emissions to define their toxicological hazard providing new and unavailable data.
The results of this integrated innovative methodology will produce a trans-disciplinary improvement in understanding the impacts of BB primary vs secondary emissions on air pollution and its toxicological hazard. These findings will allow to enhance the estimates of emission inventories and scenarios, and to offset the pros and cons of using woody biomass as energy source and its effects on air quality, climate change and health.
Acknowledgments:
This work is part of a project supported by the EC under the Horizon 2020–R&I FP through the ATMO-ACCESS Integrating Activity under GA N.101008004, and by the R+D project ATMOBE (PID2022-142366OB-I00), funded by MCIN/AEI/10.13039/501100011033/ and the "ERDF A way of making Europe” and EVER project CIPROM/20200/37.
We also thank Tatiana Gómez and M.Luisa Martinez for their work on the experiments
How to cite: Petralia, E., Gualtieri, M., Ródenas, M., D'Elia, I., Caiazzo, L., La Torretta, T. M. G., Pace, G., Piersanti, A., Stracquadanio, M., Bengalli, R., Marchetti, S., Motta, G., Vera, T., Soler, R., Borrás, E., Domínguez, B., and Muñoz, A.: Air quality and health hazard of domestic Biomass Burning heating appliances: the experiment at the EUPHORE Chamber, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11081, https://doi.org/10.5194/egusphere-egu25-11081, 2025.
Carbonaceous soot aerosol formed during the incomplete combustion of fossil fuels, biofuels, and biomasses is an important light-absorbing species containing both Black and Brown Carbon (BC, BrC). Despite being key climate forcers, soot and its BC and BrC components are still difficult to represent in models due to persisting uncertainties of its spectral optical properties, such as the complex refractive index, mass absorption/scattering/extinction cross-sections (MAC/MSC/MEC, in m2g–1) and the single scattering albedo (SSA). In particular, the dependence of optical properties on the variable composition, morphologies, and mixing state of the atmospheric soot remains poorly understood.
In order to advance on this topic, a set of experiments was performed using the 4.2 m3 CESAM simulation chamber on soot aerosol generated from a propane diffusion flame. Experiments were conceived to mechanistically investigate the dependence of soot spectral optical properties on 1/ combustion conditions and varying particle composition, and 2/ different aging processes. To investigate point 1/ the soot aerosols were generated under different combustion conditions covering both fuel–lean and fuel-rich conditions, resulting in particles with varying sizes and elemental/organic carbon (EC, OC) content. For investigating point 2/, the EC-richer soot was subjected to simulated atmospheric aging including exposure to humidity, radiation, and additional gaseous phases (O3, SO2), also inducing the formation of a coating by a second scattering aerosol phase produced via the photo-oxidation of SO2 or the ozonolysis of α-pinene.
The datasets retrieved from the chamber experiments permitted to analyse the dependence of the soot spectral absorption on their BC and BrC particle’s content, resulting in predictive relationships to use in models. Systematic simulation chamber experiments showed that the MAC has a variability associated with the EC/TC ratio in soot. The MAC at 550 nm increases for increasing EC/TC, with values of 1.0 m2g-1 for EC/TC=0.0 (BrC-dominated soot) and 4.6 m2g-1 for EC/TC=0.79 (BC-dominated soot). The Absorbing Angstrom Exponent (AAE) and the SSA at 550 nm decrease from 3.79 and 0.29 (EC/TC=0.0) to 1.27 and 0.10 (EC/TC=0.79). A combination of our results for propane soot with literature data for laboratory flame soot from diverse fuels supports a generalized exponential relationship between particle EC/TC and its MAC and AAE values, representing the spectral absorption of soot with varying maturity to lie in an optical continuum. From this, we extrapolate a MAC of 7.9 and 1.3 m2g-1 (550 nm) and an AAE (375–870 nm) of 1.05 and 4.02 for pure EC (BC-like) and OC (BrC-like) propane soot. The established relationship can provide a useful parameterization for models to estimate the absorption from combustion aerosols and their BC and BrC contributions. Results from this analysis are presented in the Heuser et al. paper available at https://egusphere.copernicus.org/preprints/2024/egusphere-2024-2381/.
How to cite: Heuser, J., Di Biagio, C., and Doussin, J.-F. and the B2C team: Simulation chamber study of the spectral optical properties of flame soot and their link to composition, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9874, https://doi.org/10.5194/egusphere-egu25-9874, 2025.
Recent studies have shown that when iron-containing mineral dust mixes with aerosols containing chloride, iron(III)chloride salts are formed enabling the photocatalytic production of Cl2 [1-3]. Work has shown that the iron salt aerosol mechanism is the largest source of chlorine radicals over the North Atlantic. The mechanism is catalytic both in iron and chlorine. Despite clear evidence from field studies, laboratory studies and modelling [2-5], significant questions remain (effect of RH, iron activity, pH limited behavior, etc.). The goal of this study is to answer these questions through experiments performed in the European Photoreactor (EUPHORE) in Valencia, Spain. The reactor is 200 m3 and utilizes natural sunlight and is therefore ideal for simulating atmospheric behavior. Measurements were collected with long-path FTIR, CIMS, OPS, SMPS, PTR-MS, ACSM, LIF-FAGE, Picarro G2108 and G2201-i as well as monitors for O3, CO, NO, NO2, NOx and HCHO. Furthermore, flask samples were collected for analysis of [CO], δ13C-CO, [CH4], δ13C-CH4 and VOCs at Utrecht University. Two sets of experiments were carried out, one to investigate the effect of the iron and chloride in the aerosols and one to investigate the mechanism using real dust samples. In the first set of experiments, solutions of FeCl3+NaCl, NaCl or FeSO4 were aerosolized to evaluate the effect of iron and chlorine separately and together. In the second set of experiments, acidic NaCl aerosols were introduced to the reactor along with aerosolized dust injections, for more realistic simulations. We will report our results concerning the rate of Cl2 production in the dark via the Fenton mechanism and by ISA.
[1] Chen et al. (2024) Environ. Sci. Technol., 58(28), 12585-12597
[2] van Herpen et al. (2023) PNAS, 120, 31
[3] Mikkelsen et al. (2024) Aerosol Research, 2, 31-47
[4] Wittmer et al. (2015) Environmental Chemistry, 12(4), 461-475
[5] Wittmer et al (2017) Journal of Atmospheric Chemistry, 74, 187-204
How to cite: Pennacchio, L., K. Mikkelsen, M., Brashear, C., Soler, R., Woods, E., Ródenas, M., Muñoz, A., van Herpen, M., Röckmann, T., and S. Johnson, M.: Measurements of photocatalytic chloride to chlorine conversion by iron-salt aerosols at the European Photoreactor (EUPHORE), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10681, https://doi.org/10.5194/egusphere-egu25-10681, 2025.
Skatole (C9H9N) is an odour-producing member of the indole family and is known to be emitted from animal excreta. It is a common emission from animal husbandry due to the practice of spreading slurry and manure as an organic fertiliser. Little is known about the atmospheric reactivity of skatole with ozone (O3), the hydroxyl radical (OH) and the nitrate radical (NO3), or the potential impacts of the oxidation products on air quality and climate.
A series of atmospheric simulation chamber experiments were performed at the Irish Atmospheric Simulation Chamber (IASC) to study the atmospheric reactivity of the gas-phase reaction of skatole with O3, OH and NO3 to determine the kinetics, products and the potential for SOA formation. The rate coefficients were determined using the relative rate method.
A time-of-flight chemical ionisation mass spectrometer (ToF-CIMS) was operated with benzene and iodide as the reagent ions. Benzene allows for the detection of hydrocarbons, aromatic compounds and nitrogen heterocycles, so it was used to detect skatole and the initial oxidation products formed. Iodide is more suited to detecting highly oxygenated compounds and was used to identify higher generation oxidation products formed in the latter stages of the reactions. A scanning mobility particle sizer (SMPS) was used to monitor the formation of secondary organic aerosols (SOA), which were also chemically analysed by ToF-CIMS fitted with a Filter Inlet for Gases and AEROsols (FIGAERO).
The results from this series of experiments provide new information regarding the atmospheric reactivity of skatole, providing a greater understanding of the impact of emissions from the practice of using slurry and manure as organic fertilisers on air quality and climate.
How to cite: Galloway, E., Campos-Pineda, M., Ruth, A., and Wenger, J.: Simulation chamber studies on the atmospheric oxidation of skatole, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15627, https://doi.org/10.5194/egusphere-egu25-15627, 2025.
Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous compounds in the atmosphere. These compounds cover a wide range of structures and chemical properties. Among them, nitro derivatives of PAHs (nitro-PAHs) are of particular interest. Nitro-PAHs are formed both by direct emissions, such as from diesel combustion engines, and by secondary reactions, such as nitration of parent PAHs. Furthermore, nitro-PAHs are recognized as toxic pollutants with adverse effects on human health [1], requiring detailed studies of their atmospheric behavior, transformations and effects.
This work focuses on three nitro-PAHs: 1-nitronaphthalene (1NN), 2-nitronaphthalene (2NN) (being these two the most abundant nitro-PAHs in the gas phase [2]), and 2-methyl-1-nitronaphthalene (2M1NN) (frequently detected in diesel exhaust [3]). The photolysis of these compounds was studied in order to understand their degradation pathways and to identify their main reaction products.
Experiments were carried out under sunlight conditions at the outdoor EUropean PHOtoREactor (EUPHORE) in Valencia, Spain.
A comprehensive suite of analytical techniques was employed, including chemical ionization mass spectrometry (CIMS), proton transfer-time of flight-mass spectrometry (PTR-ToF-MS), Fourier transform infrared (FTIR) spectroscopy, scanning mobility particle sizer (SMPS), among others. The main reaction products detected have been certain common acids such as nitrous, formic, acetic, nitric, or lactic acids. These methods provided detailed insights into the chemical transformations and effects of nitro-PAHs under atmospheric conditions, contributing to a better understanding of their environmental and health impacts. In addition, other compounds have been detected, albeit in smaller quantities, due to the partial decomposition of these nitronaphthalenes, such as 1- and 2-napthol, 2-carboxybenzaldehyde, or nitrobenzoic acid. This study sheds light on the nature of these nitronaphthalenes and their reaction mechanism in the atmosphere.
This work is part of a project that is supported by CAPOX RTI2018-097768-B-C21 funded by MCIN and co-funded by ERDF, by ATMOBE PID2022-142366OB-I00 funded by MCIN/AEI/10.13039/501100011033, by “ERDF A way of making Europe”, and by PROMETEO (EVER project) CIPROM/2022/37.
References:
[1] Benbrahim-Tallaa, L. et al., Lancet Oncol. 2012, 13, 663.
[2] Albinet, A. et al. Sci. Total Environ. 2007, 384, 280.
[3] Paputa-Peck, M.C. et al. Anal. Chem. 1983, 55, 1946.
How to cite: Blázquez, S., Soler, R., Ródenas, M., Vera, T., Borrás, E., Quaassdorff, C., Notario, A., and Muñoz, A.: Photodegradation of 1-nitronaphthalene, 2-nitronaphthalene, and 2-methyl-1-nitronaphthalene in the atmosphere, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17320, https://doi.org/10.5194/egusphere-egu25-17320, 2025.
Pulsed laser photolysis/laser-induced fluorescence (LP/LIF) was used to study the rate coefficients of the OH reaction with CO, NO, NO2 and of the HO2 reaction with NO2 in synthetic air at different water vapour concentrations (partial pressure up to 22 hPa) and at room temperature and at atmospheric pressure. The decay of the radicals was monitored by LIF, which allowed the calculation of the bimolecular rate coefficients. The rate coefficients for the reaction of OH with NO and NO2 agree very well with current NASA/JPL and IUPAC recommendations and have a high accuracy (< 5%). These rate coefficients were found to be independent of the presence of water vapour at 1 atm of total pressure. At high pressures and low water vapour mixing ratios, as in the experiments in this work, only a small effect of the collisional stabilisation by water molecules is expected. The measured rate constant of HO2 with NO2 was found to be significantly dependent on the water vapour concentration. The water dependence can be explained by an approximately two times higher rate coefficient of the reaction of NO2 with the HO2 complex with water.
How to cite: Fuchs, H., Rolletter, M., Hofzumahaus, A., and Novelli, A.: Kinetics of the termolecular reaction of OH with NO, NO2, and of HO2 with NO2 in 1 atm air at 298K and tropospheric water vapour concentrations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4738, https://doi.org/10.5194/egusphere-egu25-4738, 2025.
Deposition ice nucleation (DIN) occurs when water insoluble particles (that are not immersed in water or aqueous solution droplets) initiate the growth of ice crystals in water vapor supersaturated with respect to ice. The classical view (Fletcher, 1959) of DIN is similar to that of the heterogeneous nucleation of liquid droplets: a sufficient number of water molecules originating from the vapor phase come together at a surface within a sufficiently short period of time, forming a critical cluster that is large enough so that it does not decay but starts collecting more vapor molecules and growing. In addition to being large enough, the ice cluster must also organize into a crystalline configuration, which obviously drastically decreases the probability of a nucleation event. It therefore seems likely that an intermediate liquid phase (Ostwald, 1897) is involved in the DIN process. During the past decade, the pore condensation and freezing mechanism (Marcolli, 2014), in which liquid water condenses in the pores of insoluble aerosols and subsequently freezes, has been considered a candidate for the mechanism of atmospheric DIN events. However, it is known from laboratory studies that DIN can also occur on nonporous aerosols. In this work, we have developed a theoretical framework for describing DIN as homogeneous freezing in multilayer adsorbed water. We compare the predictions of the theory to laboratory data of critical supersaturations for DIN on nonporous silica particles at temperatures down to 208 K and find very good agreement.
Fletcher, N. H. (1959). On ice-crystal production by aerosol particles, J. Atmos. Sci., 16, 173–180.
Marcolli, C. (2014) Deposition nucleation viewed as homogeneous or immersion freezing in pores and cavities, Atmos. Chem. Phys., 14, 2071–2104,
Ostwald, W. (1897). Studien über die Bildung und Umwandlung fester Körper. 1. Abhandlung: Übersättigung und Überkaltung. Z. Phys. Chem., 22, 289-330.
How to cite: Laaksonen, A., Roudsari, G., Piedehierro, A., and Welti, A.: Deposition ice nucleation via homogeneous freezing of adsorbed water, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7329, https://doi.org/10.5194/egusphere-egu25-7329, 2025.
K-feldspar mineral dust particles have been observed to nucleate ice heterogeneously at higher supercooling compared to other atmospheric minerals. There is experimental and computational evidence pointing to the importance of high energy (100) crystallographic planes, mostly exposed in surface cracks, but the exact atomistic ice nucleation mechanism remains unknown (Kiselev et al., 2017). Recent atomistic molecular dynamics simulations did not exhibit spontaneous ice nucleation on flat (100) K-feldspar microcline surfaces (Soni and Patey, 2019). This could have been caused by inaccurate force fields, insufficient sampling time, or considering too simple surfaces that do not present active sites for ice nucleation. We try to shed new light on the phenomenon by combining molecular dynamic simulations with machine learning models. To validate the force field used in our simulations, we compare the calculated hydration layer structures with recent 3D AFM experiments at the feldspar-water interface and find good agreement between the two (Dickbreder et al., 2024). Using non-equilibrium molecular dynamics, we determine the onset freezing temperature on a large sample of K-feldspar (100) surfaces with different termination and topographical features, such as step edges, defects, and strained lattices, by looking for a potential energy jump as the simulation temperature is decreased. Machine learning models are then trained on this data set to predict the onset freezing temperature based on the characteristics of the surface, and by using feature analysis we will determine which surface characteristics enable higher onset freezing temperatures (Fitzner et al., 2020).
Dickbreder, T., Sabath, F., Reischl, B., Nilsson, R. V. E., Foster, A. S., Bechstein, R., and Kühnle, A.: Atomic structure and water arrangement on K-feldspar microcline (001), Nanoscale, 16, 3462-3473, 2024.
Fitzner, M., Pedevilla, P., and Michaelides, A.: Predicting heterogeneous ice nucleation with a data-driven approach, Nat. Commun., 1-9, 2020.
Kiselev, A., Bachmann, F., Pedevilla, P., Cox, S. J., Michaelides, A., Gerthsen, D., and Leisner, T.: Active sites in heterogeneous ice nucleation-the example of K-rich feldspars, Science, 355, 367-371, 2017.
Soni, A. and Patey, G. N.: Simulations of water structure and the possibility of ice nucleation on selected crystal planes of K-feldspar, J. Chem. Phys., 150, 214501, 2019.
How to cite: Nilsson, R., Rinke, P., Vehkamäki, H., and Reischl, B.: Hydration layer structure and ice nucleation ability of K-feldspar surfaces investigated using molecular dynamics and machine learning, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9607, https://doi.org/10.5194/egusphere-egu25-9607, 2025.
Although aqueous microdroplets have been shown to exhibit enhanced chemical reactivity compared to bulk solutions, mechanisms for these enhancements are not completely understood. Pyruvic acid (PA) is an abundant α-keto acid in aerosols, fogs, and clouds in the atmosphere, and its conjugate base, pyruvate, is an important intermediate in several metabolic pathways. Utilizing in situ micro-Raman spectroscopy as a probe, we investigated the chemistry of PA within aqueous microdroplets in a relative humidity (RH)- and temperature-controlled environmental cell. We found that PA undergoes a condensation reaction to yield mostly zymonic acid (ZA). Interestingly, the reaction follows a size-, RH- and temperature-dependent sigmoidal kinetic profile. We developed a diffusion–reaction–partitioning model to simulate the complex kinetics observed in the microdroplets. Combined experimental measurements and kinetic modeling showed that the condensation reaction of PA in microdroplets is driven by coupled surface reactions and gas-phase partitioning. Importantly, the kinetic model best fits the data when an autocatalytic step is included in the mechanism, i.e. a reaction step where the product, ZA, catalyzes the interfacial condensation reaction. Overall, the dynamic nature of aqueous microdroplet chemistry and the coupling of interfacial chemistry with gas-phase partitioning are demonstrated. Furthermore, autocatalysis of small organic molecules at the air–water interface for aqueous microdroplets, shown here for the first time, has implications for several fields including prebiotic chemistry, atmospheric chemistry and chemical synthesis.
How to cite: Li, M., Yang, S., Kumar, S., Dutcher, C., Continetti, R., and Grassian, V.: Size-Dependent Sigmoidal Reaction Kinetics for Pyruvic Acid Condensation in Single Aqueous Microdroplets, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3922, https://doi.org/10.5194/egusphere-egu25-3922, 2025.
References:
Nakao, S. et al. (2011) Secondary organic aerosol formation from phenolic compounds in the absence of NOx. Atmos. Chem. Phys. 11, 10649–10660.
Iyer, S. et al. (2023) Molecular rearrangement of bicyclic peroxy radicals is a key route to aerosol from aromatics. Nat Commun 14, 4984.
Borrás, E. Et al. (2012) L. A. Secondary organic aerosol formation from the photo-oxidation of benzene. Atmos. Environ. 47, 154–163.
How to cite: Ojala, A. and Iyer, S.: Role of the geminal diol pathway in organic aerosol formation from multigenerational aromatic oxidation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16753, https://doi.org/10.5194/egusphere-egu25-16753, 2025.
We present the development and characterization of a novel chemical ionization source useful for sensitive detection and analysis of atmospherically-relevant species in real time. The source can be used for proton-transfer-reaction mass spectrometry (PTR-MS) as well as other chemical ionization schemes generating both positive and negative analyte ions. It features fast reagent ion switching on the timescale of seconds or better, and can be operated in a broad range of ion-molecule reactor pressures (0.1 - 10 mbar) and sample flows. We couple the novel source with the high-resolution time-of-flight mass spectrometer and demonstrate sub pptv detection limits (<<1 pptv) along with a high dynamic range. We also present two weeks of ambient measurements in Thun, Switzerland using the novel ionization source switching between H3O+ and O2+ reagent ions as well as flow tube experiments which demonstrate the utility of multiple reagent ion switching between positive and negative ion modes.
How to cite: Yatsyna, V., Zgheib, I., Riva, M., Kamrath, M., Rohner, U., Alwe, H., and Lopez-Hilfiker, F.: A novel chemical ionization source for proton-transfer-reaction mass spectrometry and other chemical ionization schemes , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19764, https://doi.org/10.5194/egusphere-egu25-19764, 2025.
The formation and breakup of non-covalently-bound nitrate ion-analyte clusters is an important process in newly developed nitrate ion CIMS (Chemical Ionization Mass Spectrometry) instruments designed to detect trace molecules implicated in atmospheric aerosol and new-particle formation. Here, we show some results from using mainly classical molecular dynamics methods with empirical force fields to model these systems. These cheap methods allow us to approach the problem as a statistical one, by easily running 100s-1000s of separate simulations.
We study three different scenarios: 1) Cluster decomposition in vacuo, 2) Cluster decomposition in presence of N2, 3) Acceleration of the charged cluster by an electric field, leading to collisions with N2 and eventual decomposition. For scenarios 1 and 2, we find that the distribution of survival times has a very long tail, and can be effectively modelled as a stretched exponential, or a sum of two of them. Analysis of the survival time distribution at different initial temperatures can be used to predict the mean lifetime of the clusters at 300 K. We aim to use these data to aid the interpretation of CIMS experiments in our group[1].
Under the influence of electric field, average lifetimes vary with gas pressure and field strength [see figure]. As in similar studies of small water-ion clusters, we note that collisions between the cluster and gas can be energetic enough to cause decomposition directly in high field and low pressure[2]. However, at low field and atmospheric pressure (similar to conditions in the CIMS inlet) our results show that cluster decomposition is unlikely to occur.
[1] N. Hyttinen et al., J. Phys. Chem. A, 122, 269 (2018); S. Iyer et al., JPCA, 120, 576 (2016); A. Kumar et al., JACS 146, 15562 (2024); O. Garmash et al., Environ. Sci.: Atmos., DOI: 10.1039/d4ea00087k (2024)
[2] C.D. Daub and N.M. Cann, Anal. Chem., 83, 22393 (2011).
How to cite: Daub, C. D., Kurtén, T., and Rissanen, M.: Molecular dynamics simulations as probes of the decomposition kinetics of atmospheric molecular complexes: A case study of nitrate chemical ionization, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8620, https://doi.org/10.5194/egusphere-egu25-8620, 2025.
Particulate matter from wood combustion has a significant impact on climate and human health. Black carbon (BC) and brown carbon (BrC) are strong light absorbers that reduce the transparency of the atmosphere in the long and short wavelength range. As the aerosol ages, some of the molecular chromophores break down and the particles become less absorbent (photobleaching). On the other hand, photochemical ageing can modify organic molecules, which become light-absorbing even though they were colorless after emission. In addition, the secondary formed particles increase the light absorption and scattering of the pollution emitted by wood burning. To better estimate the contribution of particles emitted from wood combustion to the global radiation balance, it is therefore necessary to understand the optical properties of secondary particles and the changes in optical properties with ageing of primary aerosols. Limited information is available, in particular on the light absorption in the deep UV region where BrC is expected to have significant absorption. To extend the spectral information on the aerosol light absorption, the aerosol sample from wood combustion was measured with the new Aethalometer model (AE36s, Aerosol Magee Scientific), which has a spectral resolution of nine wavelengths in the 340-950 nm interval. The measurements were performed in the 200 m3 simulation chamber of the CEAM-EUPHORE research center in Valencia, Spain. Flaming and smoldering burning conditions were separately investigated and compared to diesel emission. After emission, the combustion products were introduced into the chamber, where the particles were subjected to different types of ageing (photooxidation, dark ageing). In addition to the light absorption, light scattering of the particles was measured by a nephelometer (Aurora 3000, ACOEM). The OC/BC ratio was also measured using the real-time Carbonaceous Aerosol Speciation System (CASS, Aerosol Magee Scientific). Particle formation and growth dynamics were monitored by SMPS (TSI) measurement. The optical properties of the primary emitted particles can be related to the combustion mode. Diesel emission resulted in the most absorbing aerosol over the whole wavelength range, while particles emitted from smoldering wood burning were the least absorbing, except in the UV range where BrC has high absorbance. During the photooxidation period, significant changes in the optical properties of the aerosol were observed. The absorbance of particles from smoldering emission increased significantly after the light exposure in the 470-660 nm wavelength interval. Later the absorbance decreased due to the photobleaching effect. During the photooxidation period, secondary organic aerosol formation was observed. The increase in absorbance was found to be lower than the increase in mass of the newly formed particles, while the increase in light scattering exceeded the increase in particle mass. These results suggest that the secondary aerosol was mostly transparent or had lower mass absorption efficiency but a higher scattering cross section compared to the primary emission. Therefore, the consideration of secondary formation and aging is crucial for a better understanding of the climate impact of wood combustion aerosol.
How to cite: Alföldy, B., Gregorič, A., Ježek-Brecelj, I., Ivančič, M., Ródenas, M., Soler, R., Muñoz Cintas, A., Espallardó, T. V., Borras, E., Yubero, E., Crespo Mira, J. J., and Rigler, M.: Investigation of the light absorption properties of wood combustion particles using the extended wavelength range of the new AE36s Aethalometer, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19459, https://doi.org/10.5194/egusphere-egu25-19459, 2025.
The light absorption of black carbon (BC) particles is influenced by their mixing structures and coating compositions. Liquid-liquid phase separation (LLPS) is an important microscopic phenomenon which can separate organic and inorganic phases and redistribute BC from the inorganic core (Icore) to organic coating (Ocoating). This study combines transmission electron microscopy and a 3D modeling method—Electron-Microscope-To-BC-Simulation (EMBS) to investigate how microphysical properties, such as coating compositions, Ocoating thickness, and BC position, influence the light absorption of BC particles. We found that the position of BC significantly influences its light absorption. The light absorption of BC centering in Icore is stronger below 600 nm than BC in the Ocoating. When Ocoating is considered as BrC, it reduces the light absorption of BC within Icore and Ocoating by 1.8% and 49.8%, respectively, at 350 nm due to the shielding effect, which blocks more photons from reaching the BC core. However, when accounting for the intrinsic light absorption of BrC and BC, the contribution of BrC shielding effect to individual BC particle is merely –3.0%±1.6%. The result indicates that the primary role of BrC coating still keeps light absorption rather than shielding effect in the LLPS particles. This study highlights that brown organic coating and mixing structure of BC should be comprehensively considered pertaining to optical absorption of BC-containing particles in atmospheric models.
How to cite: Zhang, Z., Wang, Y., Chen, X., Xu, L., Zheng, Z., Ching, J., Zhu, S., Liu, D., and Li, W.: Shielding effect of brown organic coating on black carbon aerosols, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2512, https://doi.org/10.5194/egusphere-egu25-2512, 2025.
Soot nanoparticles, resulting from incomplete combustion processes of fossil fuel or biomass, play a central role in many environmental and industrial phenomena, while posing major challenges for public health and global warming estimate. A better quantification of all the soot impact is thus strongly needed, which requires a better understanding of their formation and ageing processes. Experiments carried out on the structure of soot nanoparticles highlighted that their morphology is characterized by aggregation of spherical primary soot grains (carbonaceous spherules of a few to tens of nanometers in size), the resulting aggregates being of submicrometer size [1,2].
In the present work, we have used the steered molecular dynamics (MD) method [3] to investigate, at the atomic level, the coalescence of two carbonaceous spherules, aiming at modeling thus the very first steps of the aggregation process. Computations have been performed with the molecular dynamics software LAMMPS, and the AIREBO interaction potential model has been used to calculate the carbon-carbon interactions in the corresponding systems. Because it is the first time (as far as we know) that such an approach is used in this context, a thorough investigation of the influence of the intrinsic parameters of the steered MD on the results has been performed, by varying the temperature, the duration of the simulations, the spring constant values, and the thermostat. This work, which can thus be viewed as a mandatory stage for our studies on spherule aggregation, emphasizes that using steered MD is a promising approach for accurately modeling, at the atomic scale, structural changes resulting from soot aging.
[1] H. Michelsen, Probing soot formation, chemical and physical evolution, and oxidation: A review of in situ diagnostic techniques and needs, Proceedings of the Combustion Institute, 36 (2017) 717–735
[2] P. Parent et al., Nanoscale characterization of aircraft soot: A high-resolution transmission electron microscopy, raman spectroscopy, X-ray photoelectron and near-edge X-ray absorption spectroscopy study, Carbon, 101 (2016) 86–100.
[3] M. Lbadaoui-Darvas et al., Molecular-scale description of interfacial mass transfer in phase-separated aqueous secondary organic aerosol, Atmos. Chem. Phys., 21 (2021) 17687-17714
How to cite: Brosseau-Habert, N., Lbadaoui-Darvas, M., Devel, M., and Picaud, S.: Coalescence of Two Carbonaceous Nanoparticles: A Steered Molecular Dynamics Study of the First Steps of the Soot Aggregate Formation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21431, https://doi.org/10.5194/egusphere-egu25-21431, 2025.
How to cite: Kubecka, J., Trolle, G. B., Knattrup, Y., Elm, J., and Neefjes, I.: Binding free energy from umbrella sampling at ML-enhanced Born-Oppenheimer MD simulations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19209, https://doi.org/10.5194/egusphere-egu25-19209, 2025.
Posters on site: Fri, 2 May, 10:45–12:30 | Hall X5
New particle formation (NPF) plays a crucial role in the atmospheric aerosol population and has significant implications on climate dynamics, particularly in climate-sensitive zones such as the Tibetan Plateau (TP). However, our understanding of NPF on the TP is still limited due to a lack of comprehensive measurements and verified model simulations. To fill this knowledge gap, we conducted an integrated study combining comprehensive field measurements and chemical transport modeling to investigate NPF events on the southeastern TP during the pre-monsoon season. NPF was observed to occur frequently on clear-sky days on the southeastern TP, contributing significantly to the cloud condensation nuclei (CCN) budget in this region. The observational evidence suggests that highly oxygenated organic molecules (HOMs) from monoterpene oxidation participate in the nucleation on the southeastern TP. After updating the monoterpene oxidation chemistry and nucleation schemes in the meteorology–chemistry model, the model well reproduces observed NPF and reveals an extensive occurrence of NPF across the southeastern TP. The dominant nucleation mechanism is the synergistic nucleation of sulfuric acid, ammonia, and HOMs, driven by the transport of anthropogenic precursors from South Asia and the presence of abundant biogenic gases. By investigating the vertical distribution of NPF, we find a significant influence of vertical transport on the southeastern TP. More specifically, strong nucleation near the surface leads to an intense formation of small particles, which are subsequently transported upward. These particles experience enhanced growth to larger sizes in the upper planetary boundary layer (PBL) due to favorable conditions such as lower temperatures and a reduced condensation sink. As the PBL evolves, the particles in larger sizes are brought back to the ground, resulting in a pronounced increase in near-surface particle concentrations. This study highlights the important roles of anthropogenic–biogenic interactions and meteorological dynamics in NPF on the southeastern TP.
How to cite: Lai, S., Qi, X., Huang, X., Lou, S., Chi, X., Chen, L., Liu, C., Liu, Y., Yan, C., Liu, T., Li, M., Nie, W., Kerminen, V.-M., Petäjä, T., Kulmala, M., and Ding, A.: New particle formation induced byanthropogenic–biogenic interactions on the southeastern Tibetan Plateau, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1800, https://doi.org/10.5194/egusphere-egu25-1800, 2025.
This study presents the methodology and results of the chamber experiments conducted using the Korea Cloud Physics Experiment Chamber (K-CPEC) established by the Korea Meteorological Administration (KMA)/National Institute of Meteorological Sciences (NIMS) in South Korea. The research focused on warm clouds in South Korea, utilizing NaCl and CaCl2, powder-type hygroscopic materials commonly used for cloud seeding experiments. The characteristics of these particles were measured, and their effects on cloud droplet growth were observed. Detailed descriptions of the aerosol and cloud chambers at K-CPEC, along with the experimental setup and measurement instruments, are provided. The methods outlined in this study can aid in the development and evaluation of new cloud-seeding materials, enhancing the effectiveness of cloud seeding techniques.
Acknowledgments: This work was funded by the Korea Meteorological Administration Research and Development Program “Research on Weather Modification and Cloud Physics” under Grant (KMA2018-00224).
How to cite: Kim, B.-Y., Belorid, M., Cha, J. W., Kim, Y., and Kim, S.: Analysis of Hygroscopic Cloud Seeding Materials Using K-CPEC facility, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6000, https://doi.org/10.5194/egusphere-egu25-6000, 2025.
In the initial stages of atmospheric aerosol particle formation, molecules collide and stick together, forming dimers and small clusters. This is an inherently dynamic process. Molecular dynamics (MD) simulations allow us to model the dynamic behavior of these collision systems. In MD simulations, the trajectory of a system is divided into discrete timesteps, with forces on the nuclei computed at each step to propagate the system. Traditionally, these forces are calculated using classical force fields, which are highly efficient and allow for simulations of large systems over long time scales. However, classical force fields either neglect or only crudely approximate important features like chemical reactions. Atmospheric particle formation depends on proton transfers and cluster reactions to form stable aggregates, making it essential to capture these processes accurately.
Ab initio molecular dynamics (AIMD) use quantum chemistry (QC) calculations to determine the forces on nuclei at each time step. While AIMD can accurately model chemical reactions and other quantum effects, it is computationally unfeasible for anything beyond short simulations of small systems. Recently, machine learning (ML) methods have been applied to create ML potentials for MD simulations. These potentials can replicate high-level QC data while maintaining the efficiency of classical force fields. However, many ML methods rely on a local atomic environment approximation, where the potential is constructed from interactions within a user-defined cutoff radius around each nucleus. This approach fails to capture long-range interactions, which are particularly significant for polar atmospheric molecules like sulfuric acid, as these interactions typically extend well beyond the cutoff radius.
We are training ML potentials for MD simulations of collisions between atmospheric particle-forming molecules, with a focus on accurately capturing long-range interactions. A training set was generated by performing MD simulations of collisions between two sulfuric acid molecules using the semi-empirical GFN1-xTB method, followed by gradient calculations on structures along the collision trajectory. This approach ensures that the free molecules, dimers, and structures along the collision trajectory are well-represented. We then use this dataset to train ML potentials with the paiNN and PhysNet architectures. Both methods rely on the local atomic environment approximation, but PhysNet additionally incorporates long-range electrostatic interactions through learned partial charges and dispersion interactions via Grimme’s D3BJ dispersion correction. By exploring various training sets and model parameters, such as the cutoff radius for the local environment, we aim to develop ML potentials that accurately capture long-range interactions. This project serves as an initial step toward enabling large-scale MD simulations of atmospheric particle formation.
How to cite: Neefjes, I., Kubečka, J., and Elm, J.: Training machine learning potentials with accurate long-range interactions for atmospheric molecular dynamics collision simulations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9100, https://doi.org/10.5194/egusphere-egu25-9100, 2025.
The contribution of oxygenated organic molecules (OOM) in new particle formation is well known yet weakly understood. In this work, we present methods for generating optimized OOM cluster configurations. The framework for configurational sampling, optimizing, and analysing of molecular clusters is provided by JKCS program (Kubečka, Besel, et. al., 2023). Initial sampling of cluster configurations is done at semi-empirical level of theory. Local and global minimum energy configurations are found through successive rounds of filtering a subset of results and re-optimization at higher DFT levels of theory. Finally, we select the lowest energy structures to calculate the binding free energies for each cluster type.
Experimental research suggests that OOMs with more than 10 carbon atoms contribute to aerosol cluster formation. The size and complexity of OOM clusters significantly limits the number of DFT calculations we can perform, and even very large samplings of cluster configuration space do not guarantee that the global minimum is found. To improve upon existing methods, we introduce constraints to initial sampling which force hydrogen formation between molecules. We also use metadynamics simulations to search for additional local minima. OOMs are observed to cluster in configurations which maximise the number of hydrogen bonds. Thus, the binding free energies are highly dependent on the structure of each molecule and on their ability to form internal hydrogen bonds. OOMs used in this work were obtained using Gecko-AP (Franzon et. al, 2024), a RO2 + RO2 accretion product generator based on the Gecko-A software.
Machine learning force fields have the potential to predict DFT level energies with a fraction of the computational cost. However, most ML force fields do not scale well to larger molecules and fail to correctly model long-range interactions. It is also necessary to sample a dataset which covers the relevant region of the potential energy surface. We trained a neural network model to predict electronic energies for 2-OOM clusters containing 130-150 atoms. In future work we wish to train a machine learning force field which generalizes to atmospheric molecules and to decrease the prediction error close to chemical accuracy.
References
Kubečka, J., Besel, V., Neefjes, I., Knattrup, Y., Kurtén, T., Vehkamäki, H. and Elm, J. (2023) ACS Omega, 8, 45115.
Franzon, L., Camredon, M., Valorso, R., Aumont, B. and Kurten T. (2024) Atmos. Chem. Phys., 24, 11679–11699.
How to cite: Kähärä, J., Franzon, L., Kurten, T., and Vehkamäki, H.: Computational methods for generating clusters of oxygenated organic molecules , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9215, https://doi.org/10.5194/egusphere-egu25-9215, 2025.
Collisions of neutral molecules and clusters is the most prevalent pathway in atmospheric new particle formation (NPF), and therefore such collisions have direct implications on air quality and climate. Until recently, these collisions have been modeled mainly using non-interacting hard-sphere (NHS) models, which systematically underestimate collision and particle formation rates, due to omission of long-range interactions. Lately, atomistic simulations have been used to study neutral molecule-molecule and molecule-cluster collisions (Halonen et al., 2019; Yang et al., 2023), but studies on cluster-cluster collisions are still lacking despite the relevant role they can play e.g. in haze formation in polluted urban areas (Guo et al., 2014). To calculate more realistic collision rates between clusters of acid-base pairs, we have studied collisions between neutral clusters of N bisulphate and N dimethylammonium ions at T = 300 K up to N = 32 using atomistic molecular dynamics (MD) simulations. Direct simulation results are then compared against both the traditional NHS model and the newly proposed interacting hard-sphere (IHS) variant (Yang et al., 2023), respectively. We find the collision rates in the atomistic MD simulations to be enhanced by factors of 2.2 - 5.6 over the NHS results, with enhancement slowly decreasing with increasing cluster size. In contrast, the IHS model yields a constant enhancement factor of 3.4 for all collisions between same-sized clusters, which decreases with increasing cluster size ratio. Our results demonstrate how even collisions between clusters of tens of acid-base pairs at a relatively high temperature cannot be accurately modeled when long-range interactions are neglected, as convergence towards the non-interacting limit is slow when cluster radius grows. Nor can the results be explained by simple point-particle models, highlighting the importance of atomistic details of intermolecular interactions.
Guo, S., Hu, M., Zamora, M. L., Peng, J., Shang, D., Zheng, J., Du, Z., Wu, Z., Shao, M., Zeng, L., et al.: Elucidating severe urban haze formation in China, Proc. Nat. Acad. Sci. USA, 111, 17373-17378, 2014.
Halonen, R., Zapadinsky, E., Kurtén, T., Vehkamäki, H., and Reischl, B.: Rate enhancement in collisions of sulfuric acid molecules due to long-range intermolecular forces, Atmos. Chem. Phys., 19, 13355-13366, 2019.
Yang, H., Neefjes, I., Tikkanen, V., Kubečka, J., Kurtén, T., Vehkamäki, H., and Reischl, B.: Collision-sticking rates of acid–base clusters in the gas phase determined from atomistic simulation and a novel analytical interacting hard-sphere model, Atmos. Chem. Phys., 23, 5993-6009, 2023.
How to cite: Reischl, B., Tikkanen, V., Yang, H., and Vehkamäki, H.: Gas-phase collision rate enhancement factors for acid-base clusters up to 2 nm in diameter from atomistic simulation and the interacting hard sphere model, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14930, https://doi.org/10.5194/egusphere-egu25-14930, 2025.
Aerosols consist of solid or liquid particulate matter suspended in the atmosphere, varying in chemical composition and dimension. They play crucial roles in Earth’s climate system by affecting radiative forcing, cloud formation, and air quality, for instance, thus impacting both the environment and human health. Organic compounds, in particular, can largely contribute to the initial stage of particle aggregation[1, 2]. Computational chemistry methods have been fundamental to elucidating the reactions and processes involving aerosol particles in Earth’s atmosphere[3]. Nevertheless, these tools are limited by the size of the systems under investigation due to computational expenses, demanding faster and cheaper alternatives for large-scale modeling. Here, we present a scheme for a machine learning interatomic potential (MLIP) trained on the atmospherically relevant organic molecules derived from the GeckoQ dataset[1]. This model can be utilized for molecular dynamics simulations, providing results at the same level of accuracy as DFT, besides being capable of expediting the exploration of conformational chemical space. In addition, our MLIP will be trained to predict the saturation vapor pressure (a measure of a molecule’s volatility) of atmospheric molecules instead of only energies and forces. This particular property is central in atmospheric chemistry since organic molecules with low saturation vapor pressure tend to participate in particle formation processes. We anticipate the devised interatomic potential can supplant conventional quantum chemistry methods in further studies in aerosol chemistry. One of the most promising applications is the investigation of larger systems, such as accretion products (a class of large, low-volatility organic compounds resulting from chemical reactions) and clusters. Understanding the role of these products is essential in atmospheric chemistry as they are considered paramount to particle formation.
This work was supported by the VILMA (Virtual Laboratory for Molecular-Level Atmospheric Transformations) Center of Excellence, funded by the Academy of Finland under grant 13346377.
[1] Vitus Besel et al. “Atomic structures, conformers and thermodynamic properties of 32k atmospheric molecules”. In: Scientific Data 10.1 (July 2023). issn: 2052-4463. doi: 10.1038/s41597-023-02366-x. url: http://dx.doi.org/10.1038/s41597-023-02366-x.
[2] Veli-Matti Kerminen et al. “Atmospheric new particle formation and growth: review of field observations”. In: Environmental Research Letters 13.10 (Sept. 2018), p. 103003. issn: 1748-9326. doi: 10.1088/1748-9326/aadf3c. url: http://dx.doi.org/10.1088/1748-9326/aadf3c.
[3] Jonas Elm et al. “Quantum chemical modeling of organic enhanced atmospheric nucleation: A critical review”. In: WIREs Computational Molecular Science 13.5 (May 2023). issn: 1759-0884. doi: 10.1002/wcms.1662. url: http://dx.doi.org/10.1002/wcms.1662.
How to cite: Bandeira, L., Sandström, H., and Rinke, P.: Machine Learning Interatomic Potential for Atmospheric Chemistry, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15787, https://doi.org/10.5194/egusphere-egu25-15787, 2025.
Acyl peroxy nitrates (APNs) are important secondary pollutants in the troposphere, acting as reservoir for NOx (=NO2+NO). The relatively long lifetime of APNs (around 40 min at 298K) allows them to be transported from highly polluted areas to remote areas, causing an increase in both NOx and ozone concentrations on site. Various techniques are used to measure APNs in both field and laboratory experiments. These include direct methods such as Gas Chromatography (GC), and Chemical Ionization Mass Spectrometry (CIMS), as well as indirect methods such as Thermal Decomposition (TD) where APNs are decomposed and NO2 is detected.
In this contribution, the chemistry of APNs generated by the oxidation of different BVOCs (Biogenic Volatile Organic Compounds) is investigated at different levels of NOx. A series of experiments was conducted in the atmospheric simulation chamber SAPHIR, Forschungszentrum Jülich, Germany using a newly developed TD instrument which measures NO2 by Iterative Cavity enhanced DOAS (ICAD). To investigate formation of APNs from species emitted by the chamber foil (e.g., acetaldehyde) experiments injecting only methane and/or CO were conducted to obtain a baseline value for the experiments with BVOCs. These were followed by experiments with isoprene, α-pinene, and β-pinene for NO ranging between 0.3 and 9 ppbv using hydroxyl (OH) and nitrate (NO3) radicals as oxidants. Measured APNs as well as precursors and radicals were compared with results from zero-dimensional box model calculations using the Master Chemical Mechanism (MCM v 3.3.1).
How to cite: Gu, Y., Rohrer, F., Wegener, R., Pfannerstill, E. Y., Färber, M., Bohn, B., Fuchs, H., and Novelli, A.: Investigation of APNs Chemistry from the Oxidation of Volatile Organic Compounds in the Atmospheric Simulation Chamber SAPHIR, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18142, https://doi.org/10.5194/egusphere-egu25-18142, 2025.
We conducted a series of tests using the FIGAERO-HR-ToF-CIMS to assess its sensitivity to a diverse array of multifunctional organic molecules. These experiments were conducted under dark conditions in the 200 m³ outdoor chambers at EUPHORE, ensuring nearly stable concentrations of the studied compounds within a controlled environment.
The goal of these tests was to characterize the state-of-the-art instruments I-HR-ToF-CIMS coupled with the FIGAERO inlet, which allows both gas and particle phase analysis. It aimed at exploring the limits of the instruments, optimizing their performance, and ensuring the quality of their data. A series of compounds at nearly stable concentrations were measured under a range of declustering conditions, determined by the voltage settings in the transfer stages between the ion molecule reactor (IMR) and the ToF region. The concentration of the compounds was quantified using the FTIR and PTR-TOF-MS techniques.
These tests comprised two types: one involving the introduction of compounds into the chamber and another derived from biomass burning experiments. The relationship between the “dV50” and the sensitivity has been explored. Overall, higher dV50 values were observed compared to the consulted literature (Lopez-Hilkfiker et al. 2016), demonstrating the importance of characterizing each individual instrument. These results are connected to a series of compounds, among which formic acid, nitric acid, and propionic acid are included, that we aim to expand on to better understand the instrument's sensitivity. This instrumental characterization is contributing to a molecular characterization of gas- and particulate phase biomass burning compounds studied in the EUPHORE chamber.
This work is part of a project supported by the European Commission under the Horizon 2020 – Research and Innovation Framework Programme through the ATMO-ACCESS Integrating Activity (H2020-INFRAIA-2020-1) and by the R+D project ATMOBE (PID2022-142366OB-I00), funded by MCIN/AEI/10.13039/501100011033/, the "ERDF A way of making Europe”, the Valencian Regional Government (GVA) and the EVER project (CIPROM/2022/37). EUPHORE is part of the ACTRIS (Aerosol, Clouds and Trace Gases Research Infrastructure) network. Acknowledgements to the staff members Tatiana Gómez, Maria L. Martínez, and the PhD student Beatriz Domínguez for their collaboration in performing the experiments.
References:
Lopez-Hilfiker, F. D., Iyer, S., Mohr, C., Lee, B. H., D'Ambro, E. L., Kurtén, T., and Thornton, J. A.: Constraining the sensitivity of iodide adduct chemical ionization mass spectrometry to multifunctional organic molecules using the collision limit and thermodynamic stability of iodide ion adducts, Atmos. Meas. Tech., 9, 1505–1512, https://doi.org/10.5194/amt-9-1505-2016, 2016.
How to cite: Soler, R., Wood, E., Vera, T., Ródenas, M., Borrás, E., and Muñoz, A.: Characterization of APi-ToF-CIMS Sensitivity to Multifunctional Organic Molecules at EUPHORE Chambers, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18730, https://doi.org/10.5194/egusphere-egu25-18730, 2025.
How to cite: Ben Brik, A., Polat, M., O'Sullivan, N., Campos-Pineda, M., Kieft, M., Nøjgaard, J. K., Johnson, M. S., Ruth, A. A., and Wenger, J.: Secondary Organic Aerosol Formation from the Photooxidation of Naphthalene and Benzene Mixtures under Different Reaction Conditions, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21308, https://doi.org/10.5194/egusphere-egu25-21308, 2025.
