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. Aromatics contribute to this increase and accurate assessments of aromatic contributions are therefore needed for policy development. The primary and secondary steps in the OH-initiated oxidation of benzene, methylated benzenes and other aromatics are investigated to clarify recent questions on the general mechanism describing the atmospheric degradation of aromatics. We aim at a better understanding of the OH-initiated tropospheric degradation of aromatic hydrocarbons. Although this field of research has attracted a lot of attention in the last decades, there are still many open questions regarding important details of the reaction mechanism. Consequently, the impact of aromatic compounds on air quality in urban environments is still uncertain.
Laboratory techniques, theoretical calculations and simulation chambers will be used to address the following questions using new methods and experimental approaches:
1) What is the yield of different OH-adduct isomers of methyl substituted aromatics including the widely ignored ipso-isomers?
2) What is the fate of the primary OH-adducts and of secondarily formed peroxy radicals?
3) What is the yield of HO2 and RO2 radicals in consecutive reactions of the OH-adducts with O2 in the presence and absence of NO?
4) Where can the currently implemented reaction mechanism for aromatic compounds in atmospheric models be improved to make radical budgets, NOx budgets and ozone formation consistent with observations in chamber experiments?
The bilateral DFG-CNRS-project is a co-operation between the University of Bayreuth, Germany (co-ordinator), the University of Bordeaux, France, Forschungszentrum Jülich, Germany and the University of Lille, France.
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