Abstract

A description of two procedures which are used at RIVM in forecasting photochemical smog episodes is presented. Both procedures lead to the estimation of daily average oxidant (O3 + NO2) concentrations. The procedure OXPRO provides prognoses for the concentrations of "today" and procedure ZOMEREPI for the concentrations of "today", "tomorrow" and "the day after tomorrow". The overall performance of both forecasting procedures is described for the summer of 1989 (May- October), as well as the performance of predicting exceedances of threshold values (exceedence of the pre-warnbing level, 63 ppb and of the warning level, 75 ppb daily average oxidant). Recommendations to improve both procedures are given. Changes in the procedures, necessary for the planned revision in the smog alarm system in The Nehterlands (from daily average oxidant concentrations to maximum hourly average O3 concentrations), are mentioned. The procedure versions which are operational in the summer of 1990 are described.