A group additivity approach for the prediction of wavelength-dependent absorption cross-sections

Photolysis is an important loss process of carbonyl, peroxy, and nitrate species in the atmosphere. In general, photolysis rate coefficients depend on the intensity of radiation, wavelength, temperature, and the specific molecule reacting. One key source of differences in rate coefficients between different molecules is the absorption cross-section, σ, which is specific to the reactive molecule under consideration. In order to calculate rate coefficients for photolytic processes, a value of σ must be specified or estimated. To this end, a group additivity approach was developed that can be used to estimate the values of σ of species that photolyze primarily in the 290– 370 nm wavelength region. We demonstrate that this approach can be used to predict accurately unknown values of σ of species for which experimental data are not available.