Isoprene contribution to ozone production under climate change conditions in the French Mediterranean area

Tropospheric ozone is a strong oxidant which affects human health, agricultural yields, and ecosystem functioning. Thus, it is very important to understand what factors determine ozone formation in order to control air pollution. It is well known that isoprene participates in ozone formation. In this study, we assess the potential impact of climate change in the Mediterranean region on ozone concentration, through drought-related increase or decrease in isoprene emissions after 1 (short drought scenario-1 year of 35% annual rain restriction) and 3 (long drought scenario-3 repeated years of 35% annual restriction) years of drought stress. Using an original experimental dataset of Downy oak isoprene emissions for several drought conditions and idealized drought scenarios in a modeling framework, we showed that ozone concentrations follow the same pattern than isoprene emissions. The short drought scenario used an isoprene emission factor (which is the standardized emission rate at 30 degrees C and 1000 mu mol m(-2) s(-1)of photosynthetically active radiation (PAR)) 83% higher compared with natural drought and, thus, ozone concentrations increased by 5-30 mu g m(-3)(3-17%). The long drought scenario used an isoprene emission factor 26% lower compared with natural drought, and ozone concentrations accordingly decreased by 1-10 mu g m(-3)(0.6-6%). Our results showed that ozone concentration is affected by drought intensity and duration through modification of isoprene emissions indicating that drought stress should be implemented in models (predicting the BVOC emissions).