NUMERICAL-SIMULATION OF THE OZONE CHEMISTRY OBSERVED OVER FORESTED TROPICAL AREAS DURING DECAFE EXPERIMENTS

During Dynamique et Chimie de l'Atmosphere en Foret Equatoriale (DECAFE) experiments, ozone mixing ratios higher than 65 ppb have been detected in the northern equatorial continental layer above the monsoon layer. In order to understand these data we have carried out simulation experiments with a numerical model which had been developed earlier in our laboratory. These studies show that the large amounts of ozone detected cannot be only due to the chemistry of biogenic emissions in forested areas. A remote origin related to the presence of neighboring savanna areas must be considered. The amounts of remote emissions in NO and light hydrocarbons (HC) necessary to account for the observed ozone ratios should be of the order of 400-mu-g N/m2h and 1800-mu-g C/m2h, respectively. These values can be interpreted in terms of biogenic emissions and biomass combustion. On the basis of the hypothesis it is shown that biogenic emissions coming from the forest account only for 20% of the total amount of ozone measured.