In a coniferous forest area northeast of Oslo, Norway, air samples were collected by adsorption on activated carbon and analyzed by gas chromatography with a high resolution gas capillary column and flame ionization detection. During June and August 1980, seven terpenes were identified with a total concentration range of 8.8-70.7 ppbC (parts per billion, as carbon), α-Pinene, terpinene, and p-cymene occurred in the highest concentrations. A one-dimensional vertical grid model of the atmospheric boundary layer with a detailed mechanism for inorganic and organic gas phase chemical turnover was applied to assess the vertical variability of the terpene concentrations as a function of the ozone concentration, the source strength of the terpenes, the time of the day, the upwind air composition, etc. The calculations showed that very little of the terpene emissions remained airborne after 4-8 hours, in contrast to the anthropogenic hydrocarbons. It was found that the anthropogenic fraction of the hydrocarbons may dominate in concentration, even though the natural part of the source is the larger one. Emission of 2000 μg(m2 h)-1 of terpenes was calculated to give ground level concentrations of total terpenes of up to about 20 ppbC, comparable to or less than the measured concentrations. Terpene emission at this rate was shown to suppress the hydroxyl concentration compared to a model with zero terpene emissions, while the impact on ozone during daytime was negligible.