Ozone is a major component of photochemical smog, an important air quality problem. Emission of volatile organic compounds (VOCs) into the atmosphere leads to increases in the ambient ozone concentration. It would be extremely valuable to have the ability to determine how significantly a particular VOC contributes to ozone formation for both environmental and industrial purposes. A promising strategy is to assemble knowledge of the kinetics and photochemistry into detailed mechanistic models from which predictions of ozone concentrations may be obtained. Automated mechanism generation was applied. A group additivity approach was developed to estimate absorption cross sections over the wavelength region of tropospheric interest. Mechanisms were then generated automatically for various systems using different criteria for halting generation to control the explosive nature of the chemistry. A range of VOC mixtures was investigated. The models were compared to experiments, and the models were able to extrapolate well to different conditions.