title: Halogen-induced organic aerosol (XOA): a study on ultra-fine particle formation and time-resolved chemical characterization.
abstract: The concurrent presence of high values of organic SOA precursors and reactive halogen species (RHS) at very low ozone concentrations allows the formation of halogen-induced organic aerosol, so-called XOA, in maritime areas where high concentrations of RHS are present, especially at sunrise. The present study combines aerosol smog-chamber and aerosol flow-reactor experiments for the characterization of XOA. XOA formation yields from alpha-pinene at low and high concentrations of chlorine as reactive halogen species (RHS) were determined using a 700 L aerosol smog-chamber with a solar simulator. The chemical transformation of the organic precursor during the aerosol formation process and chemical aging was studied using an aerosol flow-reactor coupled to an FTIR spectrometer. The FTIR dataset was analysed using 2D correlation spectroscopy. Chlorine induced homogeneous XOA formation takes place at even 2.5 ppb of molecular chlorine, which was photolysed by the solar simulator. The chemical pathway of XOA formation is characterized by the addition of chlorine and abstraction of hydrogen atoms, causing simultaneous carbon-chlorine bond formation. During further steps of the formation process, carboxylic acids are formed, which cause a SOA-like appearance of XOA. During the ozone-free formation of secondary organic aerosol with RHS a special kind of particulate matter (XOA) is formed, which is afterwards transformed to SOA by atmospheric aging or degradation pathways.
authors.affiliation: Institute of Chemical Technologies and Analytics, Environmental and Process Analytics Division, Vienna University of Technology, Getreidemarkt 9, 1060 Vienna, Austria. johannes.ofner@tuwien.ac.at
authors.forename: Johannes
authors.initials: J
authors.lastname: Ofner
authors.affiliation: Junior Professorship in Atmospheric Chemistry, University of Bayreuth, Dr Hans-Frisch-Strasse 1-3, 95448 Bayreuth, Germany.
authors.forename: Katharina A
authors.initials: KA
authors.lastname: Kamilli
authors.affiliation: Junior Professorship in Atmospheric Chemistry, University of Bayreuth, Dr Hans-Frisch-Strasse 1-3, 95448 Bayreuth, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Held
authors.affiliation: Institute of Chemical Technologies and Analytics, Environmental and Process Analytics Division, Vienna University of Technology, Getreidemarkt 9, 1060 Vienna, Austria.
authors.forename: Bernhard
authors.initials: B
authors.lastname: Lendl
authors.affiliation: Atmospheric Chemistry Research Laboratory, University of Bayreuth, Dr Hans-Frisch-Strasse 1-3, 95448 Bayreuth, Germany.
authors.forename: Cornelius
authors.initials: C
authors.lastname: Zetzsch