In addition to peroxy and alkoxy radicals, carbonyl (i. e. substituted acetyl) radicals (R-C=O) are important short-lived radical intermediates in the atmospheric degradation of volatile organic compounds. In order to supply atmospheric modellers with the necessary input data, rate parameters for reactions of these radicals are needed. The principal reaction pathways of carbonyl radicals are either thermal decomposition or addition of O2, leading to different product distributions and thus affecting the amount of ozone formation.
In this project, state-of-the-art experimental methods are applied to quantify the branching ratio of these two pathways for a number of atmospherically important carbonyl radicals. Since thermal decomposition of R-CO generally exhibits much stronger temperature dependence as compared to O2 addition, the branching ratio of these pathways is also strongly temperature dependent. For this reason, variable temperature is an important feature of the planned experiments.
The addition pathway leads to substituted acetylperoxy radicals. For a small number of these radicals, reaction rate constants for their reactions with NO, N02, and H02 will also be determined. The effect on atmospheric chemistry of the rate parameters coming out of this project will be tested by sophisticated box model calculations. The most important radical reactions will then be implemented into a new regional atmospheric chemistry model (RACM) in order to give an account of the influence of these R-CO radicals on atmospheric chemistry. It is expected that inclusion of the experimental data from this project into atmospheric chemistry models will considerably improve the predictions about radical balances and ozone formation in the troposphere which form the basis for future ozone control strategies.
Funding SchemeCSC - Cost-sharing contracts