Heterogenous chemistry of HOx radicals

HO x radicals play an important role in the chemistry of the troposphere. They initiate catalytic cycles which lead to the oxidation and finally removal of many trace species. Measured concentrations of HO x radicals in the troposphere can not be explained by homogeneous gas-phase reactions alone, as heterogeneous loss on aerosol particles presumably plays an important role. Conventional laboratory measurements of the heterogeneous HO x decay are limited to studies under low pressures around 1 to 10 torr and dry conditions, whereas in the troposphere changing relative humidities and moderate pressures prevail. The goal of the proposed work is to determine the reaction probabilities of HO x radicals on tropospherically relevant surfaces like soot and seasalt in the laboratory under realistic conditions of relative humidities. In addition to studying the dependence on relative humidity the mechanistic aspects of theses interactions will be explored. For the experiments a flow tube apparatus coupled to a chemical ionization mass spectrometer has been set up to be employed at 100 torr and arbitrary relative humidity. The gained values can directly be employed to model the troposphere more accurately.