Laboratory Kinetics

Abstract

The chemical composition of the atmosphere is determined by a combination of chemical reactions, radiation flux, and transport of species. Processes that occur in the gaseous phase in the stratosphere include thermal gas phase reactions and photochemical reactions. Heterogeneous reactions occur between gas phase molecules in/on aerosols and polar stratospheric clouds. Models that attempt to simulate the chemical composition of the stratosphere require a number of parameters that can be measured directly in the laboratory. In the gas phase, these include reaction rate constants, product branching ratios, and photolysis quantum yields. Gas phase reaction rate constants, if determined at stratospheric temperature and pressure, are used directly in models. Photochemical reactions or heterogeneous reactions the data measured in the laboratory require transformation prior to use in model calculations. For example, quantum yield calculations used in models need to account for solar flux. In the case of heterogeneous reactions, the nature, size and distribution of aerosol particles must be considered. Advances in experimental measurements and in the understanding of the measurements themselves, have improved atmospheric models.