10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Application of Spin Traps to Detect Reactive Intermediates and Reactive Oxygen Species in Secondary Organic Aerosol
STEVEN J. CAMPBELL, Chiara Giorio, Peter J. Gallimore, Svetlana Stevanovic, Branka Miljevic, Steven Bottle, Zoran Ristovski, Markus Kalberer, University of Cambridge
Abstract Number: 558 Working Group: Aerosol Chemistry
Abstract The chemical composition and evolution of secondary organic aerosol (SOA) in the atmosphere represents one of the largest uncertainties in our current understanding of air quality. Despite vast research, the toxicological mechanisms relating to adverse human health effects upon exposure to particulate matter are still poorly understood. Studies suggest that particle bound reactive oxygen species (ROS) are a major contributor to observed health effects associated with exposure to ambient particulate matter. ROS is an umbrella term, which encompasses a large range of species including peroxides, oxidised organics, organic radicals and the transition metal-induced formation of peroxides and radicals. Several chemical assays are available for ROS detection, all of which are sensitive to a certain fraction of ROS species in aerosol. However, the role of radicals and reactive intermediates in both the formation and ageing of aerosol, as well as their contribution to the health-relevant properties of ambient aerosol, at present remains highly uncertain. We recently developed a technique to quantify organic radicals in the gas phase by stabilising them with spin traps, and subsequent analysis using various mass spectrometry techniques.1 Recently, a study by Stevanovic et al.2 introduced the profluorescent spin trap BPEAnit (9,10-bis-(phenylethynyl)-anthracene-nitroxide) which has been shown to be capable of quantifying particle-bound radicals in aerosol generated from the combustion of biomaterial and fuel.
In this work, BPEAnit is applied to study the concentrations of particle-bound radicals in SOA. Radical concentrations were estimated for SOA generated from the ozonolysis of α-pinene, β-caryophyllene and limonene in a flow tube, to probe the assays response to SOA formed from biogenic precursors typically found in the atmosphere. SOA is captured in an impinger containing the BPEAnit/DMSO assay, before subsequent analysis using fluorescence spectroscopy. Additionally, the BPEAnit spin trap assay allowed the design of experiments to probe the lifetime of radical species in α-pinene SOA, producing first estimates of organic radical decay in SOA. A pseudo-1st order rate constant of k = 7.3 ± 1.7 × 10-3 s-1 was derived, implying a radical lifetime on the order of minutes in fresh α-pinene SOA.
Furthermore, building on our recent work by Giorio et.al.,1 the spin trap PBN (N-tert-butyl-α-phenylnitrone) was used to trap Criegee intermediates (CIs) present in the aerosol phase, with the resulting adducts analysed using high performance liquid chromatography high-resolution mass spectrometry. Experiments were conducted with this method using SOA generated from β-caryophyllene ozonolysis in a flow tube, demonstrating the technique’s unique capability to detect multiple CIs present in SOA. Criegee intermediate concentrations in the aerosol phase were measured to be 4.5 ± 0.7 ng [CI]/μg SOA, providing the first estimate of condensed phase CI concentrations in SOA.
1. 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 and M. Kalberer, J. Am. Chem. Soc., 2017, 139, 3999–4008. 2. S. Stevanovic, B. Miljevic, G. K. Eaglesham, S. E. Bottle, Z. D. Ristovski and K. E. Fairfull-Smith, European J. Org. Chem., 2012, 5908–5912.