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A smog chamber study on the impact of aerosols on the photodegradation of chemicals in the troposphere

: Nolting, F.; Zetzsch, C.; Behnke, W.

Journal of Aerosol Science 18 (1987), No.1, pp.65-71
ISSN: 0021-8502
Journal Article
Fraunhofer ITA ( ITEM) ()
adsorption; aerosol; Alkan; Anatas; Aromat; Cycloalkan; Halbleiter; Hydroxylradikal; Kohlenwasserstoff; Photoabbau(heterogen); Smogkammer; TiO2; Titandioxid

In the smog chamber the photodegradation of organic compounds (gases and vapours) is observed to be dominated by OH radicals, and rate constants for the reaction of OH with n-alkanes from propane to n-nonane are determined from the simultaneous decay of the hydrocarbons. The presence of SiO2 aerosol at densities up to 4 mg m -3 does not affect the concentration of OH. In the presence of TiO2 aerosol the concentration of OH is increased by one of magnitude to 10 8cm-3. In addition a heterogeneous photodegradation of various alkanes, cycloalkanes, branched-chain alkanes and benzene-aromatics occurs inversely proportional to the vapour pressure. As expected for a heterogeneous process the data can be correlated with gas chromatographic retention times on a column, packed with TiO2. The impact of these processes (which may be due to the formation of OH on the surface of the u.v. absorbing semi-conductor, TiO2) on the chemistry of the troposphere is discussed. (ITA)