Aerosol composition and reactivity: linking composition, sources and health with health effects
About 25-75% of atmospheric aerosol particles are composed of organic material and often the majority of these organic aerosol particles are formed within the atmosphere from gaseous organic precursors via chemical and physical processes. Despite their dominance, the chemical composition, formation pathways, atmospheric reactions and effects of these organic particles are poorly characterised, mainly due to their highly complex composition with more than 10’000 organic compounds present in organic aerosol covering a wide physical-chemical parameter space. The analysis of these highly complex mixtures at trace level concentrations is a main challenge in the study of atmospheric aerosols. To better characterise aerosol effects on climate and human health an improved understanding of organic aerosol composition, evolution and sources is needed, which is only possible through an improved knowledge of particle composition.
We are using a range of laboratory experimental techniques to study fundamental aspects of aerosols formation and composition and we are characterising aerosol particle samples collected in the ambient atmosphere ranging from polluted urban to clean remote locations.
Detailed, molecular-level analysis of organic aerosol composition
To gain detailed insights into the chemical composition of organic aerosols, we are using a number of state-of-the-art analytical-chemical techniques, including ultra-high resolution mass spectrometry, liquid and gas chromatographic and optical spectroscopy methods.
We are developing new analytical-chemical techniques to obtain a comprehensive picture of the composition and evolution of organic aerosols, e.g., a novel online mass spectrometry ionisation source (Extractive Electrospray Ionisation, EESI) which allows to quantify organic and inorganic compounds in nanometer-sized aerosol particles with minimal fragmentation and matrix effects, from which other soft ionisation techniques often suffer.
This new MS ionisation technique allows to characterise particle composition at a molecular level and follow changes in particle composition with a time resolution of a few seconds to minutes. We are using EESI-MS for laboratory experiments to study aerosol composition changes.
Organic peroxide: synthesis, characterisation and quantification
It is hypothesised that organic peroxides are compounds which significantly contribute to aerosol particle toxicity due to their oxidising properties. It is expected that peroxides contribute significantly to organic particle mass, however it is challenging to analyse these compounds.
We are synthesising, characterising and quantifying atmospherically-relevant peroxides to obtain standards which allow unambiguous identification of these compounds in organic aerosol and to assess their atmospheric and health importance.
Figure 1. Schematic showing the EESI ionisation technique. A pure solvent electrospray (blue) collides with an aerosol flow (red) leading to a quantitative extraction and ionisation of aerosol components. This soft ionisation technique leads to minimal fragmentation and thus is ideal to characterise complex organic mixtures.
Responsible team members
Gallimore P.J. and M. Kalberer, Characterising an Extractive Electrospray Ionisation (EESI) source for the online mass spectrometry analysis of organic aerosols, Environ. Sci. Technol. 47, 7324−7331, 2013. https://doi.org/10.1021/es305199h
Gallimore, P.J. et al., Comprehensive modeling study of ozonolysis of oleic acid aerosol based on real-time, online measurements of aerosol composition, J. Geophys. Res. Atmos., 122, doi:10.1002/2016JD026221, 2017. https://doi.org/10.1002/2016JD026221
Steimer S.S. et al., Mass spectrometry characterization of peroxycarboxylic acids as proxies for reactive oxygen species (ROS) and highly oxygenated molecules (HOMs) in atmospheric aerosols, Anal. Chem., 89, 2873−2879, 2017. https://doi.org/doi:10.1021/acs.analchem.6b04127
Steimer, S. S., Delvaux, A., Campbell, S. J., Gallimore, P. J., Grice, P., Howe, D. J., Pitton, D., Claeys, M., Hoffmann, T., and Kalberer, M.: Synthesis and characterisation of peroxypinic acids as proxies for highly oxygenated molecules (HOMs) in secondary organic aerosol, Atmos. Chem. Phys., 18, 10973–10983, 2018. https://doi.org/10.5194/acp-18-10973-2018