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Abstract
Abstract. Reactive halogen species (RHS), such as X·, X2 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. 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.
Highlights
Besides their importance for stratospheric ozone depletion, reactive halogen species (RHS) play an important role during tropospheric ozone destruction (e.g. Jobson et al, 1994; Barrie and Platt, 1997; Foster et al, 2001)
The present study investigates physicochemical changes of secondary organic aerosol (SOA) and related precursors caused by RHS
Based on former smog chamber experiments regarding SOA formation, we have carried out a molecular reaction experiment to determine the influence of well-defined halogen species on the different types of organic aerosol
Summary
Besides their importance for stratospheric ozone depletion, reactive halogen species (RHS) play an important role during tropospheric ozone destruction (e.g. Jobson et al, 1994; Barrie and Platt, 1997; Foster et al, 2001). Jobson et al, 1994; Barrie and Platt, 1997; Foster et al, 2001) These effects were indicated by smog-chamber experiments of halogen release from NaCl Enami et al (2007) report an iodine catalysed oxidation of bromide and chloride to molecular halogen species in the troposphere. Important sources for those RHS are the halogen-release from sea-salt aerosol The formation of Cl2 by oxidation of Cl− in the presence of inorganic aerosols and a strong contribution to the overall chlorine tropospheric budget has been suggested by Zetzsch and Behnke (1993). The tropospheric reaction mechanisms of halogens significantly differ from the stratospheric ones (Platt and Honninger, 2003).
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