Organic material is the main fraction in atmospheric aerosol particles and strongly determines their effects on climate but also on human health. Due to the highly complex and poorly known composition of the organic material in aerosols there is only limited understanding of their effects in the atmosphere. Since decades, epidemiological studies have linked exposure to increased concentrations of atmospheric aerosol to mortality and hospital admissions but it remains unclear which particle properties are causing these health effects. It is often hypothesised that these negative health effects are due to redox active compound such as reactive oxygen species (ROS, defined here as inorganic and organic peroxides and radicals), which are present in aerosol particles or generated upon deposition in the lung. Established methods to quantify ROS in aerosol particles mostly rely on particles being collected on filters, followed by subsequent extraction steps and chemical analysis. Many ROS components, however, are short-lived and thus filter-based techniques risk to underestimate ROS concentrations in ambient particles.

To overcome these limitations and to understand the atmospheric variability of ROS components, we developed a range of online optical spectroscopy [1, 2, 3] and mass spectrometry [4, 5, 6, 7] methods and instruments to characterise the complexity of organic aerosol composition and the nature and concentration of the short-lived but reactive and potentially health-relevant compounds with high time resolution and without delay between particle collection and analysis. We will discuss ROS concentrations in particles generated in laboratory experiments under a range of typical air pollution conditions and from field experiments at urban locations in Asia and Europe, which indicate that a wide range of particle sources contribute to ambient ROS levels but also that photochemical processes in the atmosphere play a dominant role. Further laboratory studies will be presented, which focus on the elucidation of the molecular structure of organic radicals such as Criegee Intermediates and peroxides, an abundant but poorly characterised oxidising class of components in the gas and particle phase.

[1] F.P.H. Wragg, S.J. Fuller, R. Freshwater, D.C. Green, F.J. Kelly, M. Kalberer, Atmos. Meas. Tech., 2016, 9, 4891–4900.
[2] S. Campbell, B. Utinger, D. Lienhard, S.E. Paulson, J. Shen, P.T. Griffiths, A.C. Stell, M. Kalberer, Anal. Chem., 2019, 20, 13088-13095.
[3] S.E. Paulson, P.J. Gallimore, X.M. Kuang, J.R. Chen, M. Kalberer, D.H. Gonzalez, Sci. Adv., 2019, 5, eaav7689.
[4] P.J. Gallimore, M. Kalberer, Environ. Sci. Technol., 2013, 47, 7324−7331.
[5] C. Giorio, S. J. Campbell, M. Bruschi, F. Tampieri, A. Barbon, A. Toffoletti, A. Tapparo, C. Paijens, A. J. Wedlake, P. Grice, D J. Howe, M. Kalberer, J. Am. Chem. Soc., 2017, 139, 3999−4008.
[6] S.S. Steimer, A. Delvaux, S.J. Campbell, P.J. Gallimore, P. Grice, D.J. Howe, D. Pitton, M. Claeys, T. Hoffmann, M. Kalberer,Atmos. Chem. Phys., 2018, 18, 10973-10983.
[7] I. Kourtchev, C. Giorio, A. Manninen, E. Wilson, B. Mahon, J. Aalto, M. Kajos, D. Venables, T. Ruuskanen, J. Levula, M. Loponen, S. Connors, N. Harris, D. Zhao, A. Kiendler-Scharr, T. Mentel, Y. Rudich, M. Hallquist, J.-F. Doussin, W. Maenhaut, J. Bäck, T. Petäjä, J. Wenger, M. Kulmala, M. Kalberer, , Scientific Reports, 2016, 6, DOI: 10.1038/srep35038.