PRODUCTION OF HYDROGEN-PEROXIDE IN FOREST AIR BY REACTION OF OZONE WITH TERPENES

HYDROGEN peroxide and other hydroperoxides are thought to play a part in forest decline1-7. The toxic effects of these compounds on plants are well documented1-4 and some hydroperoxides, including H2O2, have been detected in forest air5,6 and in plant leaves7. Higher concentrations of H2O2 have been found inside forests compared with those measured close to the forest perimeter8. The reaction of atmospheric ozone with the isoprene and terpenes emitted by vegetation results in the formation of a wide variety of radicals9,10 whose subsequent reactions can contribute to the formation of hydroperoxides. We have used tunable-diode laser absorption spectroscopy to investigate the reaction of ozone with some alkenes, including isoprene and some monoterpenes, to see whether H2O2 is formed under a variety of atmospheric conditions. All the reactions studied produced H2O2 and a significant increase in the yields of H2O2 was observed when water vapour was present. The 'water effect' is the result of a direct reaction of water vapour with the Criegee biradical (the main intermediate in reactions of ozone with alkenes). From our results, we conclude that this reaction could have a more important role in the formation of H2O2 and other hydroperoxides than the self- or cross-reactions of peroxy radicals, thereby contributing to forest decline. © 1990 Nature Publishing Group.