Open Access

Show Abstract ▼

Abstract: Atmospheric aerosol hygroscopicity and reactivity play key roles in determining the aerosol’s fate and are strongly affected by its composition and physical properties. Fatty acids are surfactants commonly found in organic aerosol emissions. They form a wide range of different nanostructures dependent on water content and mixture composition. We follow nano-structural changes in mixtures frequently found in urban organic aerosol emissions, i.e. linoleic acid (LOA), oleic acid (OA), sodium oleate and fructose, during humidity change and exposure to the atmospheric oxidant ozone. Small-Angle X-ray Scattering (SAXS) was employed (Milsom et al., 2024) to derive the hygroscopicity of each nanostructure by measuring time- and humidity-resolved changes in nano-structural parameters. We found that hygroscopicity is directly linked to the specific nanostructure. Reaction with ozone revealed a clear nanostructure-reactivity trend, with notable differences between the individual nanostructures investigated. Simultaneous Raman microscopy complementing the SAXS studies revealed the persistence of oleic acid even after extensive oxidation. Our findings demonstrate that self-assembly of fatty acid nanostructures can significantly impact water uptake and chemical reactivity, thus directly affecting the atmospheric lifetime of these materials. Another focus of our studies are one-molecule thin layers of LOA and their behaviours when exposed to ozone in multi-component films at the air–water interface (Woden et al., 2024). LOA’s two double bonds allow for ozone-initiated autoxidation, a radical self-oxidation process, as well as traditional ozonolysis. Neutron reflectometry was employed to follow the kinetics of these films in real time in a temperature-controlled environment. We oxidised deuterated LOA (d-LOA) as a monolayer, and in mixed two-component films with either oleic acid (h-OA) or its methyl ester, methyl oleate (h-MO), at room temperature and atmospherically more realistic temperatures of 3 ± 1 °C. We found that the temperature change did not notably affect the reaction rate which was similar to that of pure OA. Kinetic multi-layer modelling using our Multilayer-Py package showed that neither temperature change nor introduction of co-deposited film components alongside d-LOA consistently affected oxidation rates, but the deviation from a single process decay behaviour (indicative of autoxidation) at 98 ppb is clearest for pure d-LOA, weaker for h-MO mixtures and weakest for h-OA mixtures. As atmospheric surfactants will be present in complex, multi-component mixtures, it is important to understand the reasons for these different behaviours even in two-component mixtures of closely related species. Our work demonstrates that it is essential to employ atmospherically realistic ozone levels as well as multi-component mixtures to understand LOA behaviour at low O3 in the atmosphere. Residue formation may be affected by the temperature change, potentially impacting on the persistence of the organic character at the surface of aqueous droplets. Our findings could have impacts on both urban air quality (e.g. protecting harmful urban emissions from atmospheric degradation and therefore enabling their long-range transport), and climate (e.g. affecting cloud formation), with implications for human health and wellbeing.

Open Access

Show Abstract ▼

Abstract: Water-insoluble organic material extracted from atmospheric aerosol samples collected in urban (Royal Holloway, University of London, UK) and remote (Halley Research Station, Antarctica) locations were shown to form stable thin surfactant films at an air–water interface. These organic films reacted quickly with gas-phase OH radicals and may impact planetary albedo. The X-ray reflectivity measurements additionally indicate that the film may be consistent with having a structure with increased electron density of film molecules towards the water, suggesting amphiphilic behaviour. Assuming the material extracted from atmospheric aerosol produces thin films on aqueous particles and cloud droplets, modelling the oxidation kinetics with a kinetic model of aerosol surface and bulk chemistry (KM-SUB) suggests half-lives of minutes to an hour and values of ksurf of and  cm2 s−1 for urban and remote aerosol film extracts, respectively. The superfluous half-lives calculated at typical OH atmospheric ambient mixing ratios are smaller than the typical residence time of atmospheric aerosols; thus, oxidation of organic material should be considered in atmospheric modelling. Thin organic films at the air–water interface of atmospheric aerosol or cloud droplets may alter the light-scattering properties of the aerosol. X-ray reflectivity measurements of atmospheric aerosol film material at the air–water interface resulted in calculated film thickness values to be either ∼10 or ∼17 Å for remote or urban aerosol extracts, respectively, and oxidation did not remove the films completely. One-dimensional radiative transfer modelling suggests the oxidation of thin organic films on atmospheric particles by OH radicals may reduce the planetary albedo by a small, but potentially significant, amount.

Show Abstract ▼

Abstract: Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous persistent organic pollutants that accumulate in soils because of their high affinity for soil organic matter (SOM). As these pollutants are toxic to humans and the environment, a better understanding of their fate in the environment is required. This study aimed to assess the PAH distribution within soils according to different soil fractions: the free particulate organic matter (fPOM), the occluded particulate organic matter (oPOM) and the mineral-associated organic matter (MaOM). PAH contents were measured in bulk soils and SOM fractions of alpine soils along an elevation gradient in the French Alps (Lautaret) from 1920 m to 2840 m a.s.l. A specific PAH distribution was identified, with highest PAH contents in the oPOM, followed by the fPOM, then the MaOM. Organic matter (OM) contents of each fraction can partly explain this distribution, but results of nuclear magnetic resonance (NMR) spectroscopy on fPOM and oPOM also highlighted a correlation between the PAH contents and the degree of decomposition of SOM. This indicates that the PAH distribution may be linked to the formation and transformation of fractions: (i) PAHs in the fPOM correspond to relatively recent deposits and mainly reflect the background contamination, (ii) in the oPOM are the PAHs that resist biodegradation during the transformation of fPOM into oPOM and accumulate in the oPOM; this accumulation may be further enhanced by the formation of aggregates. Finally, (iii) in the MaOM, the lower PAH contents can be explained by the different formation pathway of this fraction and its high degree of decomposition. As the PAH distribution may have an impact on their dynamics in soils, it should be taken into consideration in future research.

Open Access

Show Abstract ▼

Abstract: Hydrophobic molecules lost in water systems can have significant impacts on local ecology. Notably, the discharge of unmetabolized medications, specifically hormones, and hygiene products into effluent wastewater is a pressing environmental challenge. While selective capture of these molecules has been demonstrated by metal-organic cages (MOCs), these studies typically employ an organic solvent system that does not reflect aqueous environmental conditions. In this study, we report a rare, water-soluble, tetrahedral MOC bearing hydrosolvating sulfonate moieties alongside an aromatic naphthyl spacer. The MOC encloses a large (657 Å3) cavity that can bind a range of polycyclic structures in aqueous media. Isothermal titration calorimetry measurements support guest binding being an enthalpically driven hydrophobic binding process. The synthetic strategy employed to prepare the MOC is extensible and thus serves as a promising route to a range of large, water-soluble MOCs containing hydrophobic binding cavities with exciting prospects.

Show Abstract ▼

Abstract: The accumulation of plastic waste in the environment is an ecological disaster and will require multiple solutions to tackle the problem. Despite recent initiatives to close the plastics loop, only 9% of plastic was recycled in 2019, with the remaining waste either incinerated or accumulating in landfills or natural environments, posing hazards to both living and non-living systems. Bioplastics, derived from renewable sources, have been investigated as green alternatives to conventional fossil-based plastics. However, costly synthetic routes and low recyclability continue to challenge the growth of bioplastics. Poly(lactic acid) (PLA) is the most popular polymer for commercial bioplastics, but its recycling is limited by challenging mechanical recycling and slow biodegradation. A team of researchers from King’s College London has developed a generalisable biocatalysis engineering strategy to enhance the use of enzymes to depolymerise a broad class of plastics, in a publication recently published in Cell Reports Physical Science. This novel approach is 84 times faster than the 12-week-long industrial composting process currently used for recycling bioplastic materials.