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Unsaturated triglycerides found in food and skin oils are reactive in ambient air. However, the chemical fate of such compounds has not been well characterized in genuine indoor environments. Here, we monitored the aging of oil coatings on glass surfaces over a range of environmental conditions, using mass spectrometry, nuclear magnetic resonance (NMR), and electron paramagnetic resonance (EPR) techniques. Upon room air exposure (up to 17 ppb ozone), the characteristic ozonolysis products, secondary ozonides, were observed on surfaces near the cooking area of a commercial kitchen, along with condensed-phase aldehydes. In an office setting, ozonolysis is also the dominant degradation pathway for oil films exposed to air. However, for indoor enclosed spaces such as drawers, the depleted air flow makes lipid autoxidation more favorable after an induction period of a few days. Forming hydroperoxides as the major primary products, this radical-mediated peroxidation behavior is accelerated by indoor direct sunlight, but the initiation step in dark settings is still unclear. These results are in accord with radical measurements, indicating that indoor photooxidation facilitates radical formation on surfaces. Overall, many intermediate and end products observed are reactive oxygen species (ROS) that may induce oxidative stress in human bodies. Given that these species can be widely found on both food and household surfaces, their toxicological properties are worth further attention.

Current guidance by leading public health agencies recommends wearing a 3-layer cloth-based face mask with a middle non-woven material insert to reduce the transmission of infectious respiratory viruses like SARS-CoV-2. In this work we explore the material characteristics for a range of readily available non-woven materials and their sub-micron particle filtration efficiency (PFE), with the aim of providing evidence-based guidelines for selecting appropriate materials as inserts in cloth-based masks. We observed a wide range of ideal PFE for the tested non-woven materials, with polypropylene, Swiffer and rayon/polyester blend providing the highest PFE and breathability. Our results suggest that materials comprising loose 3D fibrous webs (e.g.flannel, Swiffer and gauze) exhibited enhanced filtration efficiency compared to compressed counterparts. Common modifications to fabrics, such as water-resistant treatment and a sewn seam were also investigated. Overall, we demonstrate that adding an appropriate non-woven material as an insert filter can significantly improve the performance of cloth-based masks, and there exist suitable cellulose-based alternatives to polypropylene.

Nitrous acid (HONO) is a major, and often the dominant, precursor to primary OH radical production in the daytime boundary layer, driving the removal of many primary pollutants and formation of secondary species such as ozone and many aerosol components. A number of photochemical HONO production mechanisms have been proposed, alongside homogeneous gas-phase reactions, to account for field observations of daytime HONO. The range of production mechanisms show varying dependencies upon precursor species such as NO2, available surfaces for heterogeneous reactions, and dark/photoenhanced aspects. Here, we exploit measurements of HONO and related species during a near-total solar eclipse as a natural perturbation to the atmospheric photochemistry to assess the characteristics of the production mechanisms occurring at an urban background location. Little variation in HONO abundance was observed in response to changing light levels during the eclipse, pointing to relatively balanced photochemical source and (well-understood) sink terms. We employ a series of simple kinetic simulations to explore the consistency of different potential source mechanisms with the observations, finding evidence for a dominant role for photochemical processing of traffic-derived NO2upon surfaces producing HONO, alongside indications of a smaller contribution from direct vehicular emissions. Other mechanisms involving dark heterogeneous reactions were not, in isolation, consistent with the observations. The critical role of NO2, ultimately derived overwhelmingly from local road traffic emissions at this location, points to significant future reductions in daytime HONO production with vehicle fleet evolution and reduction of tailpipe emissions.