EN05 Energy-related emissions of ozone precursors

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Emissions of total non-methane volatile organic compounds, nitrogen oxides, carbon monoxide and methane contribute to the formation of ground level (i.e. tropospheric) ozone. Ozone is a powerful oxidant and can have a range of adverse impacts on both human health and ecosystems.

EU-25 emissions of energy-related ozone precursors (weighted by tropospheric ozone formation potentials) decreased by 43 % between 1990 and 2004. In 2004, the production and use of energy was responsible for over three-quarters of the total emissions of ozone precursors. Of this fraction, NOx was the most significant pollutant (weighted by tropospheric ozone formation potential) contributing over 60 % of the total energy-related emissions. The changes in the emission intensity of energy-related ozone precursors are thus strongly correlated with the changes observed in NOx emissions intensity (see EN06 EU-25), as this is the most important energy-related ozone precursor.

In the EU-25, the transport sector is the dominant source of ozone precursors, and contributed 58 % of the energy-related ozone precursor emissions in 2004 (and just under half of total ozone precursor emissions). The 'energy supply', 'other' and 'industry energy' sources contributed less than 20 % each of the energy-related emissions, respectively.

The EU-25 transport sector experienced the largest decrease in ozone precursor emissions between 1990 and 2004 both in relative and absolute terms. These emission reductions were mainly due to the continuing increase in the share of passenger cars with a catalytic converter. The energy supply sector also experienced a significant decrease in emissions during this period (-41 %). The decreases in emissions from this sector (primarily NOx) can be attributed to increased use of abatement technologies and fuel-switching from coal to gas prompted by the liberalisation of the energy market, the requirements of the IPPC and Large Combustion Plant Directives and improved technology efficiencies (see also EN09; EN19 and EN27).

Total energy-related emissions of CO decreased by 54 % during the period 1990-2004 in the EU-25, again mainly in the transport sector. Decreases in CO emissions in transport occurred mainly as a result of catalytic converters on road vehicles. The remaining energy-related sectors also all reduced their CO emissions between 1990 and 2004, although in absolute (ktonne) terms, their combined emission reduction was significantly less than the reduction achieved by the transport sector.

Total energy-related NMVOC emissions decreased by 55 % in the region over the same period and accounted for less than half (48%) of the total NMVOC emissions in 2004. The majority of energy-related emissions arose from the road transport sector and petrol evaporation in the energy supply sector. NMVOC emissions from the transport sector have decreased by more than half since 1990, primarily due to the introduction of catalytic converters on cars. For the EU-15, emissions of NMVOC in 2004 are significantly higher than the 2010 targets of the NECD for EU Member States (expressed as TOFP) and substantial emission reductions are therefore still required to reach the target. However, the new Member States have made good progress in reducing NMVOC emissions, and energy-related and non-energy related emissions are already below the 2010 emission target.

Methane emissions formed less than 1 % of total ozone precursor emissions in 2004, largely as a result of its low tropospheric ozone formation potential weighting factor relative to the other pollutants. Compared with the other pollutants that contribute to ozone formation, the significance of methane is therefore relatively small. An assessment of NOx trends is included in the fact-sheet 'EN06: Energy-related emissions of acidifying substances'.