The European Environmental Agency (EEA) reports that twelve member states exceeded one or more of the emission limits set by the EU National Emission Ceilings (NEC) Directive in 2010. The directive covers four main air pollutants: sulphur dioxide (SO2), nitrogen oxides (NOx), non-methane volatile organic compounds (NMVOCs) and ammonia (NH3). Most exceedings were registered for NOx, which is mainly due to road transportation.