Emission of reactive terpene compounds from orange orchards and their removal by within-canopy processes

VOC emission from orange orchards was determined in the framework of two fi eld campaigns aimed at assessing the contribution of vegetation emissions t o tropospheric ozone formation in the Valencia Citrus belt. Branch emission from different varieties of Citrus sinensis and Citrus Clementi was domina ted by beta-caryophyllene during the summer period and by linalool during t he blossoming season (April-May). Large emission of D-limonene from soil wa s also measured. Data collected with the enclosure technique were upscaled to determine canopy emission rates of terpene compounds. Values obtained we re compared with fluxes measured by relaxed eddy accumulation. Substantial removal of beta-caryophyllene and linalool was detected during transport fr om the canopy into the atmospheric boundary layer. While within-canopy remo val of the sesquiterpene component was fully consistent with laboratory stu dies indicating the high reactivity of this compound with ozone, linalool l osses were more difficult to explain. Although high canopy fluxes of aceton e and acetaldehyde suggested linalool decomposition by gas-phase reactivity , removal by heterogeneous chemistry seems the: more likely explanation for the observed losses.