Anthropogenic impact on the ozone-forming potential of synthetic forest air

: Nolting, F.; Scheer, V.; Zetzsch, C.

Abstract
The influence of biogenic hydrocarbons on the ozone formation by the photochemical degradation of forest air was studied in this project. Simulation experiments were performed in a smog chamber with synthetic forest air that contained about 50 components according to recent field measurements in the Black Forest and near the Harz mountains. After addition of NO sub X, this mixture was irradiated by a solar simulator, and the formation of ozone was studied at different hydrocarbon/NO sub X ratios ranging from 0.5 to 25. Compared to hydrocarbonless experiments, the ozone maxima increase up to tenfold. To specify the influence of the terpenes, the experimental hydrocarbon levels were increased up to two orders of magnitude to 1000 ppbv compared to environmental levels of 13 ppbv. The ozone maximum is decreased just by a factor of two when the environmental terpene level is raised by two orders of magnitude. Simultaneously, the ozone maximum is reached more rapidly. First primary simulatio n model calculations confirm a limited contribution of the biogenic hydrocarbons to the overall ozone formation although the transformation of the terpenes contributes around 30% to the total of the hydrocarbons.