In order to achieve the 2030 objectives of the Clean Air Programme, the Directive on the reduction of national emissions of certain atmospheric pollutants has entered into force on 31 December 2016. This Directive sets national reduction commitments for the five pollutants (sulphur dioxide, nitrogen oxides, volatile organic compounds, ammonia and fine particulate matter) responsible for acidification, eutrophication and ground-level ozone pollution which leads to significant negative impacts on human health and the environment.
Source: http://ec.europa.eu/