Fig. 1. Reaction of ~-pinene with ozone and sulfur dioxide in a Teflon bag (filled with 8001 of purified air) in the dark (reaction time 6h, rel. humidity in the bag =6% , 22 ~ The actual concentration of 03, SO 2 and sulfur containing particulate matter was measured continuously during reaction In addition, experiments were carried out using the emissions of a spruce branch (Picea abies) reacting with ozone and sulfur dioxide in Teflon bags. Such an emission contains different terpenes (e.g., 30ppb o~-pinene, 53 ppb /3-pinene, 5 ppb camphene, 7ppb myrcene, 7 p p b limonene). We too found relatively rapid oxidat ion of the sulfur dioxide to sulfate within 1 h, which indicates the possible environmental significance of this process (Fig. 2). Assuming that terpene emissions close to tree surfaces (needles and bark) are relatively high, a fast reaction with ozone and subsequent oxidat ion of sulfur dioxide to sulfuric acid could be expected. We suggest a similar oxidat ion process also for nitrogen oxides resulting in nitric acid. It must be left open whether this acid format ion in the vicinity of needles and bark is harmful to trees and whether, as a consequence, the terpene emissions themselves contr ibute further damage under air pol lut ion conditions.