The familiar odors of pine forests and eucalyptus groves are caused by terpenes. Trees and shrubs contain a group of fragrant compounds called terpenes . The simplest terpene is isoprene. All other terpenes are built around carbon skeletons constructed from one or more isoprene units.
Plants emit terpenes into the atmosphere, where they react with ozone.
The possible effect of terpenes on the concentration of ozone in the troposphere has been the subject of much debate and has led to careful measurements of rates of reaction with ozone.