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J. Ofner, C. Zetsch, B. Lendl:
"Time-resolved FTIR spectroscopy of halogen-induced organic aerosol formation using an aerosol flow-reactor and 2D correlation spectroscopy";
Vortrag: ICAVS 7, Kobe, Japan; 25.08.2013 - 30.08.2013.

Reactive halogen species (RHS) are released to the atmosphere from various sources like photo-activated sea-salt aerosol1 and salt lakes2. Recent studies3,4 indicate that RHS are able to interact with precursors of secondary organic aerosol (SOA) similar to common atmospheric oxidizing gases like OH radicals and ozone. The reaction of RHS with SOA precursors like terpenes forms so-called halogen-induced organic aerosol (XOA). Due to the high reactivity, aerosol formation, initiated by RHS, seems to take place on a very short time-scale. The combination of flow reactors with FTIR spectroscopy provides access to time-resolved spectroscopy at temporal resolutions of several seconds, allowing direct spectroscopy of the formation process of XOA.
The present study uses a 50 cm aerosol flow-reactor5, equipped with a solar simulator, to investigate the time-resolved evolution and transformation of vibrational features in the mid-infrared region during the chlorine-induced formation of XOA. The aerosol flow-reactor is coupled to a Bruker IFS 113v FTIR spectrometer, using a home-made multi-reflection cell. The formation process of XOA from several organic precursor (α-pinene, limonene, Δ3-carene and p-xylene) was analyzed using 2D correlation spectroscopy6,7.
Using this setup and 2D correlation spectroscopy, the formation of halogen-induced organic aerosol could be monitored with a high temporal resolution. XOA formation is characterized by hydrogen-atom abstraction, carbon-chlorine bond formation and the formation of carboxylic acids. Several changes of the entire structure of the organic precursor, caused by the reaction of RHS, are visible. Hence, a more detailed understanding of halogen-induced organic aerosol formation and its relation to common SOA is provided.

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