Poster, AICI-HiT-SPARC Workshop, Cambridge: 16.07.2008 - 18.07.2008
Abstract:
Field experiments and laboratory studies show that atomic Br and Cl are produced from sea-salt aerosol. The halogen release is based on the uptake of gaseous HOX on aqueous, acidified salt surfaces. Br and Cl play an important role in atmospheric ozone depletion and destruction of hydrocarbons. Secondary organic aerosol and HULIS (humic like substances) may take part in these reaction cycles by halogenation and production of volatile organic halogens. Aerosol smog-chamber facilities (coolable down to -25°C) enable us to simulate the halogen release mechanism under arctic and troposphere conditions. Mechanistic and kinetic studies will be carried out to investigate the influence of secondary organic aerosols (SOA) and HULIS on bromine explosion and to determine possible halogenated gaseous and solid organic products through sea-salt activation. The salt aerosol is generated by atomizing salt solutions containing the typical Br/Cl ratio of 1/660 in seawater and increasing the Br content up to sixfold. To ensure the aqueous surface of the aerosol, the experiments were performed at relative humidities above 76%. Without the impact of organic aerosol we determined atomic Cl (up to 1x106 cm-3; depending on the Br-content of the salt solution) and OH-radical concentrations 2x106<[OH]<6x108cm-3 (depending on light source) from the simultaneous consumption of 4 reference compounds. The Br-radical concentration was calculated on the basis of the ozone depletion; from our experiments we estimate a value of [Br] = 1-3 ppt. The formation of the secondary organic aerosol and the determination of possible halogenated gaseous and solid organic products are studied using longpath-FTIR, DRIFTS, ATR, GC-MS, DMA-CNC, GC-ECD, GC-FID.