A comparison of two canopy conductance parameterizations to quantify the interactions between surface ozone and vegetation over Europe

The effect of air pollution on vegetation and the consequent changes in atmospheric chemistry are largely under-investigated; a new generation of chemical transport models fully coupled with complex land surface models is needed to better represent the feedbacks between vegetation and atmospheric chemistry. In this context, we coupled at high spatial resolution (30 km) the chemistry transport model CHIMERE with the land surface model ORCHIDEE to study the regional impact of tropospheric ozone on Euro-Mediterranean vegetation and the consequent changes in biogenic emission and ozone dry deposition owing to modifications in canopy conductance and LAI due to the ozone stress on vegetation. Results for the year 2002 show that the effect of tropospheric ozone on vegetation leads to a significant reduction of about 23% in the annual gross primary production, followed by a reduction in leaf area index. In addition, results show that CHIMERE does not correctly reproduce the activity of evergreen forests, grassland and crops during winter and fall, and consequently the dry deposition velocity is affected by this wrong pattern. On the other hand, in the coupled model, we have a better representation of vegetation activity during cold months, and the general performance of the model is improved compared to local site observations.