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Ozonolysis of a partially deuterated oleic acid monolayer floating on pure vs. salt water. Time evolution plot for ozonolysis of 17 µL 1.3 g L −1 d 18 -OA (CHCl 3 spreading solution) on pure water (green circles) and 36 g L −1 NaCl(aq) (purple squares) subphases by 323 ± 29 ppb O 3 introduced at t = 0 s at 3 ± 1 • C (pure water) or −2 ± 1 • C (salt water).
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Ozonolysis of fatty acid monolayers was studied to understand the fate of organic-coated aerosols under realistic atmospheric conditions. Specifically, we investigated the effects of temperature and salinity on the degradation of oleic acid at the air–water interface and the persistence of the aged surfactant film at the surface. The presence of a...
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... of organic residue at the air-water interface during repeated exposure to cooking emission), and after heating (orange triangles -removal of organic residue at room temperature) for the multi-ozonolysis reaction shown as a time evolution plot in Fig. 4. ing steps are omitted, and only fits shown as all three data series heavily overlap), and Fig. S6 in the Supplement focuses in on the build-up of the product monolayer by excluding the spreading R vs. Q curves from the plot and zooming in on the post-ozonolysis reflectivity data. In Fig. 5, the data points for the spreading of additional material (two series) are removed for clarity (they very closely overlap the initial spreading ...
Citations
... Oleic acid is also used as a marker for urban cooking emissions, and the ratio of oleic acid to its saturated analogue (stearic acid) is a measure of how aged a sample of urban aerosols is (Wang et al., 2020). For these reasons, oleic acid is a common model system used to study heterogeneous reactions with oxidants such as ozone and NO 3 in the laboratory and with kinetic models (Berkemeier et al., 2021;Gallimore et al., 2017;King et al., 2004King et al., , 2009King et al., , 2020Sebastiani et al., 2022;Shiraiwa et al., 2010Shiraiwa et al., , 2012Woden et al., 2021;Zahardis and Petrucci, 2007). The atmospheric lifetime of oleic acid is longer than has been predicted in laboratory experiments (Robinson et al., 2006;Rudich, 2003), with recent evidence suggesting that the steric conformation of the fatty acid can impact on its chemical lifetime (Wang and Yu, 2021). ...
Aerosols and films are found in indoor and outdoor environments. How they interact with pollutants, such as ozone, has a direct impact on our environment via cloud droplet formation and the chemical persistence of toxic aerosol constituents. The chemical reactivity of aerosol emissions is typically measured spectroscopically or by techniques such as mass spectrometry, directly monitoring the amount of material during a chemical reaction. We present a study which indirectly measures oxidation kinetics in a common cooking aerosol proxy using a low-cost quartz crystal microbalance with dissipation monitoring (QCM-D). We validated this approach by comparison with kinetics measured both spectroscopically and with high-intensity synchrotron radiation. Using microscopy, we found that the film morphology changed and film rigidity increased during oxidation. There was evidence of surface crust formation on oxidised particles, though this was not consistent for all experiments. Crucially, our kinetic modelling of these experimental data confirmed that the oleic acid decay rate is in line with previous literature determinations, which demonstrates that performing such experiments on a QCM-D does not alter the underlying mechanism. There is clear potential to take this robust and low-cost but sensitive method to the field for in situ monitoring of reactions outdoors and indoors.
... [30][31][32] The oxidative cleavage of oleic acid aerosol at the HC]CH site by ozone, a common atmospheric radical, has been particularly well documented in laboratory experiments. 25,28,31,[33][34][35][36][37][38][39][40][41][42][43] These studies give an insight into the mechanisms and kinetics of the oleic acid-ozone reaction in idealised aerosol mimics. ...
The reactivity of C 00000000 00000000 00000000 00000000 11111111 00000000 11111111 00000000 00000000 00000000 C groups in aerosols towards incoming species is highly influential to their chemical evolution and thus plays an important role in determining the properties of these aerosols and their impact on a variety of atmospheric processes. Reactions between aerosol components and gas-phase radical species often occur at the gas–liquid interface of the aerosol and thus the availability of different groups at this interface is central to determining their reactivities towards these species and the rates of these reactions. Here we look at model aerosol systems, C18 fatty acids on water, and carry out molecular dynamics simulations to determine how the presence of ‘inert’, fully saturated stearic acid molecules affects the accessibility of alkene groups within oleic acid molecules to ozone radicals. A range of stearic acid : oleic acid ratios have been studied, and a methodology has been developed in order to grow the organic layer in a random and stepwise manner that as closely as possible mimics growth in the atmosphere. The surface presence of HCCH was found to undergo a near-linear decrease as the stearic component in the slab increased, however, the coverage of other groups was found to vary in a less linear fashion and there was an increase in the overall ordering of the organic components as the stearic acid concentration increased. It was concluded that the presence of fully saturated fatty acids is unlikely to significantly alter the rate of oxidation of unsaturated species at the surface of atmospheric aerosols, however, it cannot be ruled out that differences in the overall structure of the aerosols with varying compositions could affect the rate of ozonolysis of these within the bulk of the organic layer.
... Bridging the gap between simple aerosol proxy systems and real atmospheric measurements continues to be a challenge (compare, e.g., Shepherd et al., 2022;Woden et al., 2021). 25,76 However, this study is a step toward linking the laboratory with the real world when considering the relatively novel proposition of LLC phase formation in the atmosphere. ...
The composition of atmospheric aerosols varies with time, season, location, and environment. This affects key aerosol properties such as hygroscopicity and reactivity, influencing the aerosol's impact on the climate and air quality. The organic fraction of atmospheric aerosol emissions often contains surfactant material, such as fatty acids. These molecules are known to form three-dimensional nanostructures in contact with water. Different nanostructures have marked differences in viscosity and diffusivity that are properties whose understanding is essential when considering an aerosol's atmospheric impact. We have explored a range of nanostructures accessible to the organic surfactant oleic acid (commonly found in cooking emissions), simulating variation that is likely to happen in the atmosphere. This was achieved by changing the amount of water, aqueous phase salinity and by addition of other commonly coemitted compounds: sugars and stearic acid (the saturated analogue of oleic acid). The nanostructure was observed by both synchrotron and laboratory small/wide angle X-ray scattering (SAXS/WAXS) and found to be sensitive to the proxy composition. Additionally, the spacing between repeat units in these nanostructures was water content dependent (i.e., an increase from 41 to 54 Å in inverse hexagonal phase d-spacing when increasing the water content from 30 to 50 wt %), suggesting incorporation of water within the nanostructure. A significant decrease in mixture viscosity was also observed with increasing water content from ∼104 to ∼102 Pa s when increasing the water content from 30 to 60 wt %. Time-resolved SAXS experiments on levitated droplets of this proxy confirm the phase changes observed in bulk phase mixtures and demonstrate that coexistent nanostructures can form in droplets. Aerosol compositional and subsequent nanostructural changes could affect aerosol processes, leading to an impact on the climate and urban air pollution.
... This paper describes MultilayerPy, a package written in Python, which is designed to facilitate the creation and optimisation of kinetic multi-layer models (namely KM-SUB and KM-GAP) in a modular and reproducible way. The key features are presented along with use cases focussing on the well-studied oleic-acid-ozone heterogeneous reaction system (Berkemeier et al., 2021;Gallimore et al., 2017;King et al., 2004King et al., , 2020Milsom et al., 2021bMilsom et al., , a, 2022bPfrang et al., 2011Pfrang et al., , 2017Woden et al., 2021;Zahardis and Petrucci, 2007). An educational tool has recently been created which creates and runs simple kinetic multi-layer models with two reactants (Hua et al., 2022). ...
... The oleic-acid-ozone reaction system is a well-established model compound for heterogeneous reactions of organic aerosols due to its prevalence as a cooking emission tracer (Lyu et al., 2021;Vicente et al., 2021;Wang et al., 2020) and has been the subject of numerous experimental studies King et al., 2004King et al., , 2020Knopf et al., 2005;Milsom et al., 2021b, a;Pfrang et al., 2017;Sebastiani et al., 2018;Smith et al., 2002;Woden et al., 2021;Zahardis and Petrucci, 2007). For this reason, it has been a popular system to model (Berkemeier et al., 2021;Gallimore et al., 2017;Milsom et al., 2022b;Pfrang et al., 2010Pfrang et al., , 2011Shiraiwa et al., 2010Shiraiwa et al., , 2012). ...
... 4.2 Case study 2: fitting a KM-SUB model to oleic-acid monolayer ozonolysis data, including MCMC sampling Woden et al. (2021) ozonised insoluble floating monolayers of oleic acid deposited on water (Woden et al., 2021). The reaction kinetics were followed using neutron reflectometry (NR) and fitted parameters from an interfacial model applied to the NR data -a common method of extracting kinetic information from NR experiments (King et al., 2009(King et al., , 2020Pfrang et al., 2014;Sebastiani et al., 2018;Woden et al., 2018Woden et al., , 2021. ...
Kinetic multi-layer models of aerosols and films have become the state-of-the-art method of describing complex aerosol processes at the particle and film level. We present MultilayerPy: an open-source framework for building, running and optimising kinetic multi-layer models – namely the kinetic multi-layer model of aerosol surface and bulk chemistry (KM-SUB) and the kinetic multi-layer model of gas–particle interactions in aerosols and clouds (KM-GAP). The modular nature of this package allows the user to iterate through various reaction schemes, diffusion regimes and experimental conditions in a systematic way. In this way, models can be customised and the raw model code itself, produced in a readable way by MultilayerPy, is fully customisable. Optimisation to experimental data using local or global optimisation algorithms is included in the package along with the option to carry out statistical sampling and Bayesian inference of model parameters with a Markov chain Monte Carlo (MCMC) sampler (via the emcee Python package). MultilayerPy abstracts the model building process into separate building blocks, increasing the reproducibility of results and minimising human error. This paper describes the general functionality of MultilayerPy and demonstrates this with use cases based on the oleic- acid–ozone heterogeneous reaction system. The tutorials in the source code (written as Jupyter notebooks) and the documentation aim to encourage users to take advantage of this tool, which is intended to be developed in conjunction with the user base.
... 8 Key components of surface-active organic aerosols are fatty acids; [9][10][11][12][13][14] it is important to note that phase behaviour especially for fatty acids is highly temperature dependent, 8 and little data are available for temperatures lower than ambient e.g. ref. 15, which are particularly relevant for surfactants in clouds. [8][9][10][11][12][13][14] Atmospheric fatty acids include saturated (such as palmitic acid 16 ) and unsaturated acids in particular oleic acid which is found both in marine [17][18][19] and cooking [20][21][22] aerosols. ...
The ageing of organic-coated aqueous aerosols at night is investigated by reacting NO3 with binary surfactant mixtures floating on water. The surfactants are oleic acid (OA), methyl oleate (MO) and stearic acid (SA). Deuterated surfactants mixed with hydrogenous surfactants were studied using neutron reflectometry to determine the reaction kinetics of organic two-component monolayers with NO3 at the air–water interface for the first time. We measured the rate coefficients for OA monolayers, mixed with hydrogenous co-surfactant MO or SA to be (3 ± 1) × 10⁻⁸ cm² per molecule per s or (3.6 ± 0.9) × 10⁻⁸ cm² per molecule per s and MO monolayers mixed with hydrogenous co-surfactant OA or SA to be (0.7 ± 0.4) × 10⁻⁸ cm² per molecule per s or (3 ± 1) × 10⁻⁸ cm² per molecule per s. The initial desorption lifetimes of NO3, τd,NO3,1, were 8 ± 3 ns, 14 ± 4 ns, 12 ± 3 ns and 21 ± 10 ns. The approximately doubled desorption lifetime for MO–SA compared to the other mixtures is consistent with a more accessible double bond associated with the larger area per molecule of MO in the presence of SA facilitating NO3 attack. The significantly slower reactive loss of MO–OA compared to a MO monolayer demonstrates that multi-component surfactant mixtures need to be studied in addition to single-component monolayers. Such a retarded decay would cause the residence time to change from ca. 4 to 22 minutes associated with increased transport distances of surfactant species together with any other pollutants that may be protected underneath the surfactant film.
... The trough design has been subsequently modified to include a barrier to allow for monolayer compression and the capability for temperature control. [53] The measured neutron reflectivity profiles are easy to interpret, as the interfacial region does not feature any of the superfluous layers such as silicon, silicon dioxide or gold that are typically present for floating bilayers formed on solid substrates. The profiles are particularly sensitive to the thickness of the water layer between the monolayer and the bilayer and the APM of the lipids in the bilayer. ...
Hypothesis: The attractive interaction between a cationic surfactant monolayer at the air-water interface and vesicles, incorporating anionic lipids, is sufficient to drive the adsorption and deformation of the vesicles. Osmotic rupture of the vesicles produces a continuous lipid bilayer beneath the monolayer. Experimental: Specular neutron reflectivity has been measured from the surface of a purpose-built laminar flow trough, which allows for rapid adsorption of vesicles, the changes in salt concentration required for osmotic rupture of the adsorbed vesicles into a bilayer, and for neutron contrast variation of the sub-phase without disturbing the monolayer. Findings: The neutron reflectivity profiles measured after vesicle addition are consistent with the adsorption and flattening of the vesicles beneath the monolayer. An increase in the buffer salt concentration results in further flattening and fusion of the adsorbed vesicles, which are ruptured by a subsequent decrease in the salt concentration. This process results in a continuous, high coverage, bilayer suspended 11A beneath the monolayer. As the bilayer is not constrained by a solid substrate, this new mimetic is well-suited to studying the structure of lipid bilayers that include transmembrane proteins.
... Hydroperoxides and aldehydes originate from a subsequent decomposition of these energetically unstable products [87,88]. In the case of ozonized oleic acid, the decomposition reaction results in 1-nonanal, 9-oxononanoic acid, azelaic acid and nonanoic acid [74,89]. Further studies would be necessary to unravel the contribution of these and further compounds of the ozonized oleic acid to its antimicrobial activity. ...
In this study, an amplicon metagenomic approach was used to determine the effect of repeated treatments with ozonized oleic acid on the microbial community of grapevine carpoplane. Differences in community composition of treated vineyards were compared to non-treated and conventionally treated samples regarding the prokaryotic and eukaryotic microbiome at two developmental stages (BBCH 83, BBCH 87). The results showed effects both on occurrence and on abundance of microorganisms and the community assembly. Wine-relevant genera such as Acetobacter and members of the former genus Lactobacillus could be identified as part of the natural microbiota. The impact of the new viticultural treatment on these organisms was assessed in liquid culture-based microtiter assays. Therefore, we investigated an array of two acetic acid bacteria (AAB), four lactic acid bacteria (LAB) and nine saccharomyces and non-saccharomyces yeasts. Brettanomyces bruxellensis, Saccharomyces cerevisiae, Pediococcus sp. and Acetobacter aceti revealed the highest sensitivities against ozonized oleic acid (LIQUENSO® Oxygenat). Culture growth of these organisms was significantly reduced at an ozonide concentration of 0.25% (v/v), which corresponded to a quarter of the concentration used in the vineyard. The metabarcoding approach in combination with complementary in vitro assays allow new insights into treatment effects on the community and species scale.
... 118,322-325 Pfrang et al. 323 found that mixtures of oleic acid and sodium oleate in aqueous NaCl droplets formed 3D self-assembled nanostructures at the gas-liquid interface, and these structures slowed heterogeneous reactions with ozone. Woden et al. 325 tested the inuence of both temperature and salinity on the ozonolysis of oleic acid at the air-water interface. The resulting lm, containing nonanoic acid, azelaic acid, and 9-oxononanoic acid, persisted at the surfaces of pure water and 36 g L À1 NaCl (aq) only if temperatures were below $12 C or below freezing, respectively. ...
Surfactants are surface-active molecules or ions that can often be found at the surface of atmospheric aerosol particles. Some surfactants, such as biomolecules in marine aerosol and cooking oils in urban aerosol, are directly emitted into the atmosphere, whereas others form from secondary reactions in the atmosphere. Environmentally relevant surfactants have long been studied in laboratory experiments and computational models, but recent developments in mass spectrometry, spectroscopy, imaging, and colorimetry have greatly expanded measurements of surfactants in ambient aerosol. This review focuses on advances surrounding the following themes: techniques for measuring and modeling surfactants on aerosol particles, the morphology of surfactant-coated aerosol particles, the impact of surfactants on cloud droplet activation and ice nucleation, multiphase reactions and photochemical reactions on surfactant-coated particles, and finally, field observations of surfactants on ambient particulate matter. An exciting area for future work is the continued advancement of single-particle techniques to simultaneously monitor morphology and composition of individual aerosol particles. Along with an expansion of field sampling campaigns, more laboratory studies of increasingly complicated aerosol systems are needed to bridge the gap between complex observations from the field and fundamental investigations in the laboratory. Characterizing surfactants, films, and coatings on atmospheric aerosol particles can provide insights relevant to how particulate matter impacts climate, air quality, and human health.
... 10,20,21 This makes it a suitable proxy compound for laboratory and model investigations into reactive organic aerosol systems. [22][23][24][25][26][27][28][29][30] The oleic acid-ozone heterogeneous oxidation system is well-studied and a simplied summary of the principal reaction and products is presented in Scheme 1. 28 As a surfactant, oleic acid can decrease the surface tension of an aqueous particle, affecting the ability of the particle to take up water and form a cloud droplet. [31][32][33] Oleic acid molecules, being amphiphilic, can arrange into a range of lyotropic liquid crystal (LLC) phases in contact with water and in the presence of its sodium salt. ...
... Previous work has focussed on monolayers of deuterated oleic acid on an aqueous sub-phase, 27,55,59 self-assembly in an oleic acid-sodium oleate proxy in large levitated particles 24,60 and reaction kinetics in capillaries coated with micron-scale lms of this lamellar phase proxy down to ca. 0.6 mm. 23 Kinetic modelling of these experiments has shown that the chemical lifetime of oleic acid could increase by days upon selforganisation. ...
Atmospheric aerosol particles can be coated with organic materials, impacting aerosol atmospheric lifetime and urban air quality. Coatings of organic materials are also found on indoor surfaces such as window glass. Oleic acid is a fatty acid surfactant that is abundant in cooking and marine aerosol emissions. Under ambient conditions it can self-assemble into lamellar bilayers (stacks) with its sodium salt. We found that nano-scale oleic acid–sodium oleate films spin-coated onto solid silicon substrates form a mixed-phase area of lamellar stacks and amorphous films. The coatings were subjected to simulated atmospheric ageing (ozonolysis and humidity changes) while the surface structure was followed by neutron reflectometry. We found that the orientation of lamellar stacks, which is known to affect the diffusivity of small molecules through them, was sensitive to humidity both in oxidised and pristine films. Lamellar bilayer stacks in oxidised films acquired ∼11-fold more water under humid conditions (>80% relative humidity) compared to the unoxidised film, demonstrating a significant increase in film hygroscopicity after oxidation. Lamellar stacks, consisting only of starting materials, persisted at the end of simulated atmospheric ageing. These findings for atmospherically relevant nano-scale films corroborate previous work on micrometre-scale layers, thus demonstrating that fatty acid self-assembly could significantly increase the atmospheric lifetime of these molecules. The persistence of such semi-solid surfactant arrangements in the atmosphere has implications for the climate as well as urban and indoor air pollution.
... This is a long-standing discrepancy and suggests that some physical process is inhibiting the ageing of such aerosols. For these reasons, oleic acid has been the compound of choice for laboratory studies into aerosol heterogeneous oxidation (Gallimore et al., 2017;King et 40 al., 2020;Milsom et al., 2021bMilsom et al., , 2021aPfrang et al., 2017;Woden et al., 2021;Zahardis and Petrucci, 2007). ...
Atmospheric aerosols influence the climate via cloud droplet nucleation and can facilitate the long-range transport of harmful pollutants. The lifetime of such aerosols can therefore determine their environmental impact. Fatty acids are found in organic aerosol emissions with oleic acid, an unsaturated fatty acid, being a large contributor to cooking emissions. As a surfactant, oleic acid can self-organise into nanostructured lamellar bilayers with its sodium salt, and this self-organisation can influence reaction kinetics. We developed a kinetic multi-layer model-based description of decay data we obtained from laboratory experiments of the ozonolysis of coated films of this self-organised system, demonstrating a decreased diffusivity for both oleic acid and ozone due to lamellar bilayer formation. Diffusivity was further inhibited by a viscous oligomer product forming in the surface layers of the film. Our results indicate that nanostructure formation can increase the reactive half-life of oleic acid by an order of days at typical indoor and outdoor atmospheric ozone concentrations. We are now able to place nanostructure formation in an atmospherically meaningful and quantifiable context. These results have implications for the transport of harmful pollutants and the climate.
