The scientific importance of atmospheric reactive gases and aerosols and the particular case of the Mediterranean region

Chemistry of the lower Earth's atmosphere is subject to intensive research because it is recognized as an important component of the Earth system, especially at the regional scale, impacting human health and mortality, the regional climate, visibility, building materials, terrestrial ecosystems, as well as freshwater and marine aquatic ecosystems. It is also deeply related to anthropogenic pressure, especially in a climate change context. Air quality studies over the Mediterranean region show relatively high levels of atmospheric particulate matter (PM) and tropospheric ozone compared with northern and central regions of Europe. Both anthropogenic (transport sector, industrial processes, energy production, biomass burning, among others) and natural (African dust, resuspension, sea spray, forest fires, living vegetation, bio-secondary organic compounds) emissions, as well as orographic and climatic factors, contribute to making the specificity of the Mediterranean atmospheric environment. High levels of atmospheric background concentrations of pollutants are observed, and impacts of air pollution on climate, health, and ecosystems are already of concern and could still increase in the future.