Emission and flux of terpenoids released from the terrestrial ecosystems present in the Pianosa Island

For the first time, the emission of individual BVOC released from a Mediterranean ecosystem has been assessed and the results obtained have been directly compared with fluxes measured with the mixed box (MB) approach. The study was conducted in Pianosa, a very small and flat island located in the Tyrrhenian sea, between the coasts of Central Italy and the Corsica Island. Due to the substantial lack of man-made emission and the restricted access, terrestrial vegetation represents in this island the main source of hydrocarbons. This allows to use simple methodologies to estimate and measure the emission of individual BVOC in the atmosphere. Due to the limited number of emitting species, the total emission was estimated by up-scaling to ecosystem level the information obtained with branch enclosures. Data obtained suggested that the basal emission of total isoprenoids generated from the island was one order of magnitude smaller than that estimated in the pine-oak forest ecosystem of Castelporziano (ca. 0.2 mg C m-2h-1). á-Pinene was the major component emitted and accounted, by itself, for more than 40% of the total isoprenoid emission. Daily profiles of emission were calculated for the two days when the air masses were depleted in anthropogenic compounds, after traveling for two days over the open sea. Results obtained in these days indicated that á-pinene was the only component displaying an emission (ca. 0.1 mg C m-2 h-1) sufficiently high to generate detectable concentrations (0.01-0.03 ìg C Nm-3) in the atmospheric boundary layer (ABL). Fluxes determined using the MB approach substantially confirmed the estimates made by up-scaling to ecosystem level the emission from terrestrial vegetation, although a difference of a factor of two was observed between the calculated emission and the measured fluxes. Reasons explaining these differences will be analyzed and critically discussed.