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Has files: Yes × Subject: Volatile organic compounds ×

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    Highly Oxygenated Organic Molecules (HOM) from Gas-Phase Autoxidation Involving Peroxy Radicals: A Key Contributor to Atmospheric Aerosol
    (Washington, DC : ACS Publ., 2019) Bianchi, Federico; Kurtén, Theo; Riva, Matthieu; Mohr, Claudia; Rissanen, Matti P.; Roldin, Pontus; Berndt, Torsten; Crounse, John D.; Wennberg, Paul O.; Mentel, Thomas F.; Wildt, Jürgen; Junninen, Heikki; Jokinen, Tuija; Kulmala, Markku; Worsnop, Douglas R.; Thornton, Joel A.; Donahue, Neil; Kjaergaard, Henrik G.; Ehn, Mikael
    Highly oxygenated organic molecules (HOM) are formed in the atmosphere via autoxidation involving peroxy radicals arising from volatile organic compounds (VOC). HOM condense on pre-existing particles and can be involved in new particle formation. HOM thus contribute to the formation of secondary organic aerosol (SOA), a significant and ubiquitous component of atmospheric aerosol known to affect the Earth's radiation balance. HOM were discovered only very recently, but the interest in these compounds has grown rapidly. In this Review, we define HOM and describe the currently available techniques for their identification/quantification, followed by a summary of the current knowledge on their formation mechanisms and physicochemical properties. A main aim is to provide a common frame for the currently quite fragmented literature on HOM studies. Finally, we highlight the existing gaps in our understanding and suggest directions for future HOM research. © 2019 American Chemical Society.
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    About the Development and Dynamics of Microdischarges in Toluene-Containing Air
    (Dordrecht : Springer Science + Business Media B.V., 2019) Brandenburg, Ronny; Jahanbakhsh, Sina; Schiorlin, Milko; Schmidt, Michael
    The development of microdischarges and the inception dynamics of subsequent microdischarges in an electrode arrangement consisting of a metal pin and a hemispherical dielectric-covered electrode, operated in air with a small toluene admixture, is studied. The discharge is operated with sinusoidal high voltage. A gated ICCD camera and a current probe enable the recording of images and current pulses of the single microdischarges, respectively, while the spatio-temporally resolved development is measured with a multi-dimensional time-correlated single photon counting technique. The overall discharge dynamics changes significantly if a concentration of 35 ppm toluene is added to dry air. A lower high voltage amplitude than in dry air is needed for stable discharge operation. This can be explained by the lower ionization energy of toluene compared to molecular oxygen and nitrogen. The microdischarge development is the same with or without admixture, i.e. a positive (cathode directed) streamer mechanism is observed. Lower mean power is dissipated into the discharge when toluene is admixed. The main effect caused by toluene admixture is the suppression of high-energy microdischarges in case of the cathodic pin half-cycle of the sinusoidal high voltage. The influence on the inception voltage by additional ionization mechanisms and volume memory effects, the consumption of energetic electrons for toluene decomposition reactions, and the modification of the surface by plasma treatment are discussed as possible reasons.