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Simulation of atmospheric photochemistry in the presence of solid airborne aerosols

Simulation der atmosphärischen Photochemie in Gegenwart fester, luftgetragener Aerosole
: Zetzsch, C.

Zellner, R.:
Formation, distribution and chemical transformation of air pollutants
Weinheim/Bergstraße: VCH Verlagsgesellschaft, 1987 (Dechema-Monographien 104)
ISBN: 3-527-10991-9
Book Article
Fraunhofer ITA ( ITEM) ()
aerosol; Alkan; Aromat; atmosphärische Aufenthaltsdauer; Chloralken; Chloratom; Geschwindigkeitskonstante; Langmuir-Theorie; n-Alkan; photochemischer Smog; Photohalbleiter; Retentionszeit; Smogkammer

A smog chamber for the simulation of tropospheric chemistry in the presence of aerosols was installed. Thermostating of lid and bottom of the cylindrical, vertically arranged vessel of 2.4 cubic meters volume facilitates aerosol residence times of 1 day in the presence of simulated sunlight, and of 2 days in the dark. At initial mass concentrations up to 3 mg mE-3, the aerosols SiO2, TiO2, Fe2O3, coal fly ash and NaCl are investigated in a photosmog of NOx and hydrocarbons. SiO2 and fly ash show inert behaviour. The rate constants of OH, observed in the presence of these aerosols, agree well with literature values. In the smog chamber (and in a further 0.5 cubic meter chamber) rate constants for further compounds are determined for the first time, among them the n-alkanes up to n-hexadecane. In the presence of TiO2, at 2 mg mE-3, concentrations of OH enhanced by one order of magnitude are observed, reaching levels of 10 E8 cm E-3. In addition, a heterogeneous photodegradation occurs wi th an intensity inversely proportional to the vapour pressure of the hydracarbons: for compounds, less volatile than n-hexane, the heterogeneous photo-degradation surpasses the reaction with OH in the gas phase. A similar, possibly vapour pressure-dependent photodegradation is detected with low volatile aromatics in the presence of Fe2O3. In the presence of NaCl aerosol, Cl atoms are formed, competing and surpassing the contribution of OH to the consumption of alkanes after a few hours. (ITA)