Clean air for future generations : a multi-model investigation of air quality projections

In order to investigate future air quality, the anthropogenic emissions scenarios developed in the framework of the Global Energy Assessment were implemented in six regional and global atmospheric chemistry transport models. Using decadal simulations and meteorological fields representative of the current (early 21st century) conditions we could isolate the impact of changes in anthropogenic emissions on the modelled concentrations of atmospheric pollutants. The strengths of the present work include: use of realistic emission scenarios (as opposed to sensitivity studies), similar in their design and development to IPCC projections, yet more appropriate for air pollution studies ; implementing a variety of chemistry transport models, including regional and global scale tools so that an ensemble representative of a range of scales could be derived, hence providing a better understanding of model uncertainty ; presenting the results in an "exposure-based" framework, with policy-relevant indicators specifically designed for health and ecosystem exposure assessment. The discussion includes a specific focus for Europe as well as a global overview. We find that, in Europe, O3 and PM10 concentrations decrease by 2030 compared to 2005 with a stronger improvement for the scenario including climate policy enforcement in addition to the current air quality legislation. However, for some models and scenarios a relative increase of O3 remains in areas saturated in nitrogen oxides. Nevertheless exposure indicators weighted by the population density or land use fraction unambiguously show the overall improvement in terms of total pollution cumulated over sensitive areas. The global simulations offer an interesting insight into the very different trajectories over developing countries as well as sensitivities studies on the impact of changing methane background concentrations