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* '''The EU Emissions Trading System (ETS)<ref name="ets" />:''' The EU Emissions Trading System is a Cap and Trade system implemented at the European level. Based on the polluter pays principle, the main objective of this system is to reduce greenhouse gasses and air pollutant emissions by implementing a system of yearly emissions quotas allocated for each company (the cap). On a common market based on the law of supply and demand, these quotas can be exchanged between companies (trade system) according to their needs. To ensure a the successful achievement of the objectives to reduce the emissions, the system includes more and more countries and companies each year.

The European Commission estimated an important return on investment near a ratio of 20 times of the cost. Either an order of €3.3 billion a year on direct costs (energy and heat generation, less dependency on fossil fuels, health costs) and on the indirect costs (health improvement) which can range from €4 to €140 billion. Moreover, the benefits will also concern the exposure of the EU territory and citizens to air pollutants and their risks. Thus, the aim is to decrease the exposure to eutrophication from 62% of the EU area to 44% of the area, a decrease of 29% of the area exposed to the eutrophication. Concerning the exposure to acidification, a decrease of 79,36% of the EU area exposed to acidification - from 110.000 km² to 27.500 km² - has been estimated.Thus the Clean air package’s aim is to have a common mass investment to ensure the best reduction of risks and costs.