Air pollution is a complex environmental and social issue at the European and international levels. It poses a high risk to human health as it is related to cardiorespiratory disease and cancer. At the same time, it impacts the economy, adding to the health expenditure and reducing productivity. Air pollution also has important effects to the natural environment affecting ecosystems, soil and water quality and vegetation. Moreover, it interacts with the climate, since several main pollutants behave as climate forcers.