Organic cooking emissions account for up to 10% of the particulate emissions in the UK. The emissions are fine particles which stay present in the air that originates from cooking processes. Such particles can have an impact on health, air quality, and the climate. In megacities, environmental studies have identified cooking as a key source of man-made emissions.
Dr Christian Pfrang (University of Birmingham) and Dr Adam Squires (University of Bath) have recently published a study on how the persistence of cooking aerosols can be altered by the natural process of oxidation. The research was performed in collaboration with the Central Laser Facility (Dr Andrew Ward), colleagues from Diamond Light Source (Nick Terrill), and Published in the Royal Society of Chemistry's Faraday Discussion.
For the study, oleic acid was used as a representative of unsaturated fatty acids in the atmosphere. Urban particulate matter coatings, such as that of oleic acid, are known to be found on aerosol surfaces. Thus, the scientists aimed to investigate the effect of thickness of oleic acid coating using Small-Angle-X-ray Scattering (SAXS), Raman Spectroscopy, and Wide-Angle X-ray Scattering (WAXS).
The researchers measured the cooking aerosol's reactivity in different forms. SAXS/WAXS/Raman spectroscopy techniques were applied, which allowed the researchers to probe the cooking aerosol's structure at a nanometer scale and simultaneously its chemical composition. CLF scientist from Octopus group, Dr Andy Ward, applied a novel approach to the experiment by building a Raman spectrograph on Diamond's I22 micro-focus beamline, which allowed simultaneous spectroscopy and X-ray scattering measurement. The Raman spectroscopy used a green (532 nm) laser source which was coupled to a custom optical probe enabling access to the organic material. Collaboration and detailed planning with the I22 beamline scientists ensured that interlocking of the beamline was in place to provide our usual laser safety measures when performing the experimental work.
The study demonstrated that once oleic acid is oxidized it becomes unreactive, meaning that the outer particulate coating becomes inert and so essentially forms an outer crust. The fatty acid in the centre of the particle becomes protected from oxidation and no longer reacts, and so it stays in the atmosphere for longer. Thus, the study highlights the possibility of increased lifetime of these cooking aerosols, especially in high population environments, which can have an impact on air quality, human health, and even climate because it may contribute to rising particulate concentrations.
The full publication is available to be viewed in the Royal Society of Chemistry's Faraday Discussions.