Direct studies of HOx- and NO2 formation in the oxidation of oxygen containing hydrocarbon radicals under tropospheric conditions

The oxidation of hydrocarbons in the troposphere under NOx rich conditions is associated with ozone formation via conversion of NO to NO2 in reactions with HO2/RO2 in the subsequent photolysis of NO2. The extent of NO/NO2 conversion is hydrocarbon specific and changes with i.e. chain length in the case of n-alkanes. In the present project a laser spectrometric techniques has been developed which allows the direct determination of NO/NO2 conversion by measurements of OH and NO2 growth in the oxidation of individual hydrocarbons. This technique has been applied to all n-alkanes up to n-hexane. It is found that for the simplest alkanes (CH4, C2H6, C3H8) ΔNO2/Δh.c. equals 2.0. For all larger alkanes ΔNO2/Δh.c. increases. These results provide the basis for the derivation of parameterized, lumped mechanistic expressions for the description of ozone formation in chemical/dynamical modells as well as the delineation of ozone formation potentials of individual hydrocarbons. (orig.). 19 refs