Atmosphärische Aerosolprozesse - Labor- und Modelluntersuchungen -
It was found that during the heterogeneous reactions of NO2, HNO3, and N2O5 with mineral dust the first reaction step involves surface OH-groups. During all reactions surface saturation was observed. The kinetics of the reaction of NO2 with Al2O3 was found to be approximately second order in NO2. The kinetics of the HNO3 and N2O5 reactions are first order. It could be shown that after surface saturation had occurred the reactivity could be widely restored by exposure to water vapor. The reaction of NO2 is slow and is of negligible importance in the atmosphere. The reactions of HNO3 and N2O5 with mineral dust appear to be fast and should be included in atmospheric models.
During the reactions of NO2 and HNO3 with soot surface species with the functional groups R-CO, R-NO2, R-ONO, and R-ONO2 could be identified. The reaction order of the NO2 and HNO3 reactions are smaller than one. The uptake kinetics could be fitted using a fast and a slow saturation reaction. Because for both processes the number of reactive surface sites is limited, the soot reactions play only a minor role in the photooxidant budget of the atmosphere.
Within this work an autocatalytic halogen activation mechanism was developed, which was shown to represent a significant source for reactive bromine and chlorine in the marine boundary layer. The reactions were included in a photochemical box model and halogen radical concentrations and ozone destruction rates were calculated for marine boundary layer conditions. In addition, a new sulfur-(IV) oxidation mechanism involving HOCl and HOBr was proposed which would dominate and significantly increase the sulfur oxidation in the marine boundary layer. The bromine and chlorine activation scheme was investigated in combination with a newly developed iodine reaction scheme. It was shown that the chlorine and bromine activation was enhanced by iodine chemistry. Further the mechanism describes the enrichment of particulate iodine in the chemical form of iodate, which has been observed in the marine environment.