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Atmospheric Chemistry of volatile and semi-volatile organic compounds

Aromatics are a major contributor to the formation of regional ozone in urbanized areas. Toluene, for example, is ranked fourth of all volatile organic compounds in terms of overall contribution to ozone production in northern Europe, behind butane, ethane and ethanol, based on a recent trajectory model calculation by Derwent et al. (2003). The calculations also demonstrate that episodic peak ozone concentrations are decreasing in Europe, primarily because of motor vehicle emission controls brought in during the 1990s. However, there is a clear and continuing increase in background ozone concentration that derives from anthropogenic effects on hemispheric atmospheric chemistry.
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EUROCHAMP-Integration of European Simulation Chambers for Investigating Atmospheric Processes

The fundamental objective of the project is the integration of the most important environmental reaction chambers in Europe for studying atmospheric processes into a Europe-wide infrastructure. These facilities were created by multinational initiatives to study the impact of atmospheric processes on regional photochemistry, global change, as well as cultural heritage and human health effects under most realistic conditions. Participating laboratories are from Germany, France, Great Britain, Spain, Ireland, Switzerland, Sweden, Italy and Denmark. The main research activities of the Atmospheric Chemistry Research Laboratory at Bayreuth are the characterisation of aerosols and the investigation of aerosol reactions (organic coatings of POPs (persistent organic pollutants) and deliquescent sea-salt) in indoor photoreactors. A low-temperature aerosol simulation chamber facility (LOTASC) has been constructed in order to investigate the aerosol-partitioning of semi-volatile compounds at low temperature (down to -25°C). This will allow simulating tropospheric photochemistry, including cirrus clouds. Furthermore, every institution participates in building up a database of smogchamber experiments, see http://eurochamp-database.es/.
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Heterogeneous chemistry on secondary organic aerosols and HULIS

Gas to particle conversion forms so called secondary aerosols. Secondary Organic Aerosols (SOA) are formed by reaction of Volatile Organic Compounds (VOCs), which are released by plants and trees. Gaseous isoprenoids like á-pinene are oxidized by atmospheric reactants like ozone or hydroxyl radicals and form particles by nucleation and aggregation. A special class of SOA are so-called Humic Like Substances (HULIS). HULIS have similar structures to humic acides which are well known from soil chemistry. While HULIS are formed by shorttime atmospheric oxidation and nucleation, humic substances are formed slower at dark conditions. SOA and HULIS play an important role in atmospheric chemistry. They are very important reactants in atmospheric trace gas reactions. Mechanisms of heterogeneous atmospheric reactions of SOA and HULIS are hardly known. Within the HALOPROC project (Natural Halogenation Processes in the Environment Atmsophere and Soil) the halogenation of SOA and HULIS by seasalt activation is topic of research. As part of the EGER project (ExchanGE processes in mountainous Regions), aiming to investigate trace gas exchange between atmosphere and ecosystems, formation of nitrous acid is investigated in laboratory experiments and measured in the atmosphere.
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Photochemistry of seasalt aerosol and halogen activation

Seasalt aerosol, which is mainly formed through bubble bursting, is a very important natural source of atomic chlorine and bromine in the troposphere. These halogens are best known to destroy ozone by intermediate halogen oxides, described in the atmospheric halogen cycles. The release of reactive halogens from seasalt aerosol can be described as follows: HOBr is transformed to molecular Br or BrCl, these gas phase molecules leave the aerosol 2 particle and are photolysed. By destruction of ozone halogen oxides like BrO and ClO are formed. BrO reacts with the atmospheric hydroperoxyl radical (HO ) to form 2 HOBr. HOBr is adsorbed by the seasalt aerosol and halogens are released again (“Bromine Explosion”).
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