Aerosol-halogen interaction: Change of aerosol optical properties

Reactive halogen species, released by sea-salt activation, offer a class of reactants of utmost importance for heterogeneous reactions with organic aerosols. To study the interaction of organic aerosols with these halogen species, secondary organic aerosol (SOA) was produced from α-pinene, catechol and guaiacol (Ofner et al., 2011) in a 700 L glass smog-chamber and in a 3500 L Teflon smog-chamber at defined environmental conditions (with and without simulated sunlight and ozone at various humidities). The well-characterized and aged organic aerosols were exposed to molecular halogens in the presence of UV/VIS irradiation and to halogens released from simulated natural halogen sources to study the halogen-SOA interaction process. Various spectroscopic methods were used to investigate optical and structural changes of the organic aerosols. Diffuse reflectance UV/VIS spectroscopy was employed to characterize optical properties in the UV/VIS spectral range. Using FTIR spectroscopy both, the aerosol formation and transformation process and, using ATR (Attenuated Total Reflectance) spectroscopy, the appearance of functional and structural elements of the particulate phase were characterized. Using Temperature-Programmed-Pyrolysis Mass-Spectroscopy (TPP-MS) and Ultra-high resolution FourierTransform/Mass-Spectroscopy (ICR-FT/MS), degrees of halogenations and single halogenated molecules could be determined.