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Authors: Arangio, Andrea Mario
Title: Role of reactive oxygen species in multiphase chemistry of organic aerosols in the atmosphere
Online publication date: 25-Apr-2017
Language: english
Abstract: Reactive oxygen species (ROS) play a central role in both atmospheric and physiological processes. In the atmosphere, ROS are produced by photochemical and multiphase reactions, and are important species in the removal of air pollutants. In biological systems, ROS act as mediators of intracellular signaling, but they can also cause oxidative stress by damaging lipids, proteins, and DNA. At the atmosphere-biosphere interface such as biogenic aerosols and lung lining fluid, chemical interactions of ROS pose feedback loops involving the Earth system, climate, and public health. Multiphase processes of ROS are controlled by reactions and mass transport of species between gas, liquid and solid phases. Despite their importance, kinetics and chemical mechanisms that govern the interactions between atmospheric and physiological processes are not yet well understood and characterized. Multiphase reactions of OH radicals are among the most important pathways for chemical aging of organic aerosols in the atmosphere. Reactive uptake of OH by organic compounds has been investigated extensively, but the kinetics of mass transport, chemical reactions as well as their interdependence are still not understood. The kinetic multilayer model of gas–particle interactions in aerosols and clouds (KM-GAP) resolves these processes by explicitly taking into account solubility, diffusivity and reactivity of each species involved. In this work, KM-GAP was applied to experimental data from OH exposure of coated-wall flow tube of levoglucosan (LG) and abietic acid (AA), which serve as surrogates and molecular markers of biomass burning aerosol (BBA). For both LG and AA, the bulk diffusion coefficients were found to be approximately 10-16 cm2s-1, reflecting their amorphous semisolid state. It was shown that the OH uptake by these films was governed by the reaction at or near the surface and could be kinetically limited by bulk diffusion of the organic reactants. Through these diffusion coefficients, the chemical half-life of LG in 200 nm diameter particles in a biomass burning plume was estimated to increase from one day to one week depending on the relative humidity. In BBA particles transported to the free troposphere, the chemical half-life of LG can exceed one month due to slow bulk diffusion at low temperature. Ambient and laboratory-generated secondary organic aerosols (SOA) were found to form substantial amounts of OH radicals upon interaction with liquid water, which can be explained by the decomposition of organic hydroperoxides. The molar OH yield from SOA formed by oxidation of terpenes (α-pinene, β-pinene, limonene and isoprene) is 0.1 % upon extraction with pure water and increases to 1.5 % in presence of Fe2 ions due to Fenton-like reaction. These findings imply that the chemical reactivity and aging of SOA particles is strongly enhanced upon interaction with water and iron. In the human respiratory tract, the inhalation and deposition of SOA particles may lead to a substantial release of OH radicals, which may contribute to oxidative stress and play an important role in the adverse health effects of atmospheric aerosols. A wide range of particle-associated radicals were detected and quantified in size segregated atmospheric particles using electron paramagnetic resonance (EPR) spectroscopy. Particle samples were collected using a cascade impactor at a semi-urban site in Mainz, Germany, in May-June 2015. Concentrations of environmentally persistent free radicals (EPFR), most likely semiquinone radicals, were found to be in the range of (1-7) × 1011 spins μg-1 for particles in the accumulation mode. Coarse particles with a diameter larger than 1 μm did not contain substantial amounts of EPFR. Using a spin trapping technique, ROS formed upon extraction of the particle samples in water were determined to be (0.1-3) × 1011 spins μg-1. By deconvolution of EPR spectra ROS released by submicron particle samples were found to include OH, superoxide (O2-), carbon- and oxygen-centered organic radicals. OH was instead the dominant species for coarse particles. EPR spectra derived from ambient particulate matter were compared with those of mixtures of organic hydroperoxides, quinones and iron ions. By means of the EPR spectra comparison and chemical analysis with liquid chromatography mass spectrometry (LC-MS), the particle-associated ROS were suggested to be formed by decomposition of organic hydroperoxides interacting with transition metal ions and quinones contained in atmospheric humic-like substances (HULIS). indent Ambient particles were collected using a cascade impactor also in Beijing, China in January 2016 and in Nagoya, Japan in April 2016. The average EPFR concentration contained in particles with size diameter range of 100 - 560 nm was 1.3 × 1012 spins μg-1 in Beijing, which is almost one order of magnitude higher than the average EPFR concentrations in Mainz (2.3 × 1011 spins μg-1), and in Nagoya (4.7 × 1011 spins μg-1). The difference is remarkably high for particles with lower cut-off sizes of 320 nm. The result reflects stronger aerosol emission from biomass and coal combustion in Beijing compared to fossil fuels and traffic emissions in Nagoya and Mainz. Identification and evaluation of chemical stability of radical adducts resulting from spin trap EPR experiments is a difficult task to accomplish. Electron Paramagnetic Resonance for Spin TrappIng Chemical Kinetics (EPR-STICK) was developed, which is a new MATLAB toolbox to perform EPR spectral processing, radical quantification, spectra deconvolution and kinetic modeling of radical reactions. The toolbox was applied to experimental data to investigate the kinetics of the spin trapping, efficiency and yield of radicals formed upon decomposition of tert-butyl-hydroperoxide catalyzed by iron ions.
DDC: 540 Chemie
540 Chemistry and allied sciences
Institution: Johannes Gutenberg-Universität Mainz
Department: FB 09 Chemie, Pharmazie u. Geowissensch.
Place: Mainz
Version: Original work
Publication type: Masterarbeit
License: in Copyright
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Extent: 117 Seiten
Appears in collections:JGU-Publikationen

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