ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-12-5787-2012 Halogenation processes of secondary organic aerosol and implications on halogen release mechanisms Ofner J. 1 Balzer N. 1 Buxmann J. 2 Grothe H. 3 Schmitt-Kopplin Ph. 4 Platt U. 2 Zetzsch C. 1 Atmospheric Chemistry Research Laboratory, University of Bayreuth, Germany Institute for Environmental Physics, University of Heidelberg, Germany Institute of Materials Chemistry, Vienna University of Technology, Austria Research Unit Analytical Biogeochemistry, Helmholtz Zentrum Munich and Chair of Analytical Food Chemistry, TUM, Freising/Weihenstephan, Germany 04 07 2012 12 13 5787 5806 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/12/5787/2012/acp-12-5787-2012.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/12/5787/2012/acp-12-5787-2012.pdf

Reactive halogen species (RHS), such as X·, X<sub>2</sub> and HOX containing X = chlorine and/or bromine, are released by various sources like photo-activated sea-salt aerosol or from salt pans, and salt lakes. Despite many studies of RHS reactions, the potential of RHS reacting with secondary organic aerosol (SOA) and organic aerosol derived from biomass-burning (BBOA) has been neglected. Such reactions can constitute sources of gaseous organohalogen compounds or halogenated organic matter in the tropospheric boundary layer and can influence physicochemical properties of atmospheric aerosols. <br><br> Model SOA from α-pinene, catechol, and guaiacol was used to study heterogeneous interactions with RHS. Particles were exposed to molecular chlorine and bromine in an aerosol smog-chamber in the presence of UV/VIS irradiation and to RHS, released from simulated natural halogen sources like salt pans. Subsequently, the aerosol was characterized in detail using a variety of physicochemical and spectroscopic methods. Fundamental features were correlated with heterogeneous halogenation, which results in new functional groups (FTIR spectroscopy), changes UV/VIS absorption, chemical composition (ultrahigh resolution mass spectroscopy (ICR-FT/MS)), or aerosol size distribution. However, the halogen release mechanisms were also found to be affected by the presence of organic aerosol. Those interaction processes, changing chemical and physical properties of the aerosol are likely to influence e.g. the ability of the aerosol to act as cloud condensation nuclei, its potential to adsorb other gases with low-volatility, or its contribution to radiative forcing and ultimately the Earth's radiation balance.

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