Changes in European surface ozone air quality over the 21st century

Surface ozone is a criteria air pollutant, formed by photochemical reactions involving nitrogen oxides (NO_x) and volatile organic compounds (VOCs). Despite recent reductions in the surface ozone burden following precursor emission controls (predominantly concerning NOx) the recent European air quality report published by the European Environment Agency (EEA) highlights that to date still 17 EU member states are reporting ozone concentrations that exceed the target value set for the protection of human health (120 µg/m³, maximum daily 8-hour average (MDA8) not to be exceeded more than 25 times per year (3-year average)). In total, 20 percent of all ozone monitoring sites showed ozone concentrations exceeding the EU target value for the protection of human health, and only 5% of monitoring sites showed ozone concentrations in compliance with the more stringent WHO target value. Here we focus on past and future changes in European surface ozone abundances in a set of simulations performed with the Geophysical Fluid Dynamics Laboratory (GFDL) chemistry-climate model CM3. First, we evaluate the general model performance for the recent past by comparing model output to observations available from the EEA Airbase database. The evaluation is performed on the basis of interpolation of the historic site level observations to a grid of 2.5° x 2°, matching the dimensions of the CM3 model. Our results for the recent past show that the modelled ozone abundances are biased high compared to observations. Therefore, we apply a suite of correction techniques (quantile mapping, delta function) to obtain modelled ozone fields in agreement with observations. Emanating from remediated model data the correction functions derived are applied to transient (2006-2100) simulations following selected Representative Concentration Pathways (RCPs). Using these bias-corrected future simulations we illustrate next potential changes in future European surface ozone air pollution over the course of the 21^st century.