10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Development of a Physiologically Relevant On-Line Chemical Assay to Quantify Aerosol Oxidative Potential
STEVEN J. CAMPBELL, Daniel Lienhard, Battist Utinger, Angharad Stell, Suzanne E. Paulson, Markus Kalberer, University of Cambridge
Abstract Number: 552 Working Group: Health Related Aerosols
Abstract It is currently estimated that up to 0.3 million premature deaths per year in Europe and 2.1 million deaths worldwide are the result of exposure to ambient particles with an aerodynamic diameter less than 2.5 μm (PM2.5). However, the identification of the physical and chemical particle properties responsible for these observed adverse human health effects remains a challenge. Toxicological studies suggest that some of the observed adverse health effects derive from the occurrence of reactive oxygen species (ROS) and other oxidising particle components in cells, added directly through inhalation of PM or formed by reactions of particle components in vivo.1 Oxidising, particle-phase components include a wide range of chemical species such as transition metals (e.g. iron, nickel and copper), a range of organic compounds including polyaromatic hydrocarbons (PAHs), quinones, peroxides and radicals, complicating their analysis.
In order to protect the body against these oxidising species, lung cells generate antioxidants such as ascorbic acid (AA) which are present in the respiratory tract lining fluid (RTLF); these anti-oxidants act as the first line of defence against oxidising components in aerosol particles. When these antioxidants are depleted (defined as oxidative stress), a number of cellular responses occur, including inflammatory reactions.
Offline methods have been developed previously to characterise oxidising particle components by quantifying the decrease of antioxidants.2 These methods are based on the analysis of filter extracts sampled typically for several hours to days. The time delay between sampling and analysis in these off-line methods, which might be hours to days, may result in an underestimation of oxidising particle component concentrations or adverse health effects as some of the more reactive species might be converted to more stable compounds before analysis. In addition, the effect on composition caused by the filter extraction remains uncertain.
In this work, a new on-line method to quantify the oxidation of ascorbic acid in synthetic RTLF was developed by adapting an existing home-built instrument, which quantifies ROS based on a different reaction system (DCFH)3. This new instrument combines the advantages of on-line measurements (i.e. high time resolution of a few minutes) with the more physiologically relevant assay to estimate health-relevant oxidising aerosol properties. The applicability of this method to the oxidation of ascorbic acid by secondary organic aerosol (SOA) generated from the ozonolysis of α-pinene in a flow tube is demonstrated. The instrument response to particles containing a mixture of SOA and iron sulphate seed particles was also investigated, illustrating a synergistic enhancement of the oxidation of ascorbic acid when organic SOA and iron are sampled simultaneously, compared to SOA and iron sulphate particles separately.
1. F. J. Kelly and J. C. Fussell, Atmos. Environ., 2012, 60, 504–526. 2. K. J. Godri, R. M. Harrison, T. Evans, T. Baker, C. Dunster, I. S. Mudway and F. J. Kelly, PLoS One, 2011, 6. 3. F. P. H. H. Wragg, S. J. Fuller, R. Freshwater, D. C. Green, F. J. Kelly and M. Kalberer, Atmos. Meas. Tech., 2016, 9, 4891–4900.