Application of artificial neural networks to modeling and prediction of ambient ozone concentrations

The deterministic modeling of ambient O-3 concentrations is difficult because of the complexity of the atmospheric system in terms of the number of chemical species; the availability of accurate, time-resolved emissions data; and the required rate constants. However, other complex systems hare been successfully approximated using artificial neural networks (ANNs). In this paper, ANNs are used to model and predict ambient O-3 concentrations based on a limited number of measured hydrocarbon species, NOx compounds, temperature, and radiant energy. In order to examine the utility of these approaches, data from the Coastal Oxidant Assessment for Southeast Texas (COAST) program in Houston, TX, have been used. In this study, 53 hydrocarbon compounds, along with O-3, nitrogen oxides, and meteorological data were continuously measured during summer 1993. Steady-state ANN models were developed to examine the ability of these models to predict current O-3 concentrations from measured VOC and NOx concentrations. To predict the future concentrations of O-3, dynamic models were also explored and were used for extraction of chemical information such as reactivity estimations for the VOC species. The steady-state model produced an approximation of O-3 data and demonstrated the functional relationship between O-3 and VOC-NOx concentrations. The dynamic models were able to the adequately predict the O-3 concentration and behavior of VOC-NOx-O-x system a number of hourly intervals into the future. For 3 hr into the future, O-3 concentration could be predicted with a root-mean squared error (RMSE) of 8.21 ppb. Extending the models further in time led to an RMSE of 11.46 ppb for 5-hr-ahead values. This prediction capability could be useful in determining when control actions are needed to maintain measured concentrations within acceptable value ranges.