Impact of tropospheric ozone on the Euro-Mediterranean vegetation

The impact of ozone (O₃) on European vegetation is largely under-investigated, despite huge areas of Europe are exposed to high O₃ levels and which are expected to increase in the next future. We studied the potential effects of O₃ on photosynthesis and leaf area index (LAI) as well as the feedback between vegetation and atmospheric chemistry using a land surface model (ORCHIDEE) at high spatial resolution (30km) coupled with a chemistry transport model (CHIMERE) for the whole year 2002. Our results show that the effect of tropospheric O₃ on vegetation leads to a reduction in yearly gross primary production (GPP) of about 22% and a reduction in LAI of 15-20%. Larger impacts have been found during summer, when O₃ reaches higher concentrations. During these months the maximum GPP decrease is up to 4gCm^-2day^-1, and the maximum LAI reduction is up to 0.7m²m^-2. Since CHIMERE uses the LAI computed by ORCHIDEE to estimate the biogenic emissions, a LAI reduction may have severe implications on the simulated atmospheric chemistry. We found a large change in O₃ precursors that however leads to small changes in tropospheric O₃ concentration, while larger changes have been found for surface NO₂ concentrations.