Air Quality in Europe

This chapter reviews the status of emissions of key air pollutants regulated in the European Union (EU) and assesses emissions trends over the period 2005 to 2019. The main economic sectors that contributed to total emissions in 2019 are identified for key pollutants, while reductions in emissions over the period 2005 to 2019 are set against developments in Gross Domestic Product (GDP). It also includes an assessment of the relationship between emissions of key air pollutants and their concentrations in ambient air.

Policy Context

In the EU, emissions of air pollutants are regulated under the National Emissions reduction Commitments Directive (Directive (EU) 2016/2284) the NEC Directive. Emission ceilings for 2010 to 2019 were previously established for four key air pollutants: nitrogen oxides (NO_x), non-methane volatile organic compounds (NMVOCs), sulphur dioxide (SO₂) and ammonia (NH₃). These ceilings remained applicable until the end of 2019. New emissions reduction commitments now apply for the period 2020-2029, and more stringent commitments apply for 2030 onwards. The scope was extended to include fine particulate matter (PM_2.5), a pollutant that significantly impacts health. Under the NEC Directive, Member States have reported annual emissions inventory information from 1990 – or in the case of PM_2.5 from 2000. The most recent data were reported for 2019. The EEA produces annual briefings on the reporting status under the NEC Directive, assessing EU progress towards these policy targets.

At pan-European level, emissions to air are regulated under the United Nations Economic Commission for Europe (UNECE) Convention on Long-range Transboundary Air Pollution (Air Convention). Under the Air Convention, the Gothenburg Protocol sets emission ceilings for NO_x, NMVOCs, sulphur oxides (SO_x) and NH₃. Parties to the Air Convention must reduce their emissions to the levels set out in the protocol and report emission data for numerous air pollutants. The EEA compiles the annual EU emission inventory report under the Air Convention, in cooperation with the EU Member States and the European Commission. The Gothenburg Protocol formed the basis for the EU NEC Directive for the period 2020-29.

Key Air Pollutants

Air pollutants may be categorised as primary or secondary. Primary pollutants are directly emitted to the atmosphere, whereas secondary pollutants are formed in the atmosphere from precursor pollutants through chemical reactions and microphysical processes. Air pollutants may have a natural, anthropogenic or mixed origin, depending on their sources or the sources of their precursors.

Key primary air pollutants include particulate matter (PM), black carbon (BC), SO_x, NO_x (including nitrogen monoxide and nitrogen dioxide, NO₂), NH₃, carbon monoxide (CO), methane (CH₄), NMVOCs, including benzene, and certain metals and polycyclic aromatic hydrocarbons, including benzo[a]pyrene (BaP).

Key secondary air pollutants are PM, ozone (O₃), NO₂ and several oxidised volatile organic compounds (VOCs). Key precursor gases for secondary PM are SO₂, NO_x, NH₃, and VOCs. Ground-level ozone is formed from chemical reactions in the presence of sunlight, following emissions of precursor gases, mainly NO_x, NMVOCs, CO and CH₄. These precursors can be of both natural and anthropogenic origin.

Fine particulate matter	PM2.5
Particulate matter with a diameter of 10 µm or less	PM10
Black carbon	BC
Sulphur dioxide	SO2
Nitrogen oxides	NOx
Ammonia	NH3
Carbon monoxide	CO
Methane	CH4
Non‑methane volatile organic compounds	NMVOCs
Benzo[a]pyrene	BaP
Arsenic	As
Cadmium	Cd
Lead	Pb
Mercury	Hg
Nickel	Ni

Total EU-27 emissions declined in 2019 for all pollutants, maintaining the overall downward trend observed since 2005. Figure 1 shows the trend in total emissions of the main air pollutants in the EU-27, indexed as a percentage of their value in the reference year 2005, set against EU‑27 GDP as a percentage of the 2005 value.

Emissions of PM₁₀ and PM_2.5 fell by 27% and 29% respectively over the period from 2005 to 2019. Notably, the lowest reduction in emissions (-8%) in this period is seen for NH₃, an important precursor gas contributing to the formation of secondary particulate matter. While emissions of NH₃ fell by 2% from 2018 to 2019, this followed a period of increasing emissions from 2015 to 2018. Emissions of CH₄ also declined by only 17%, with CH₄ being an important greenhouse gas driving climate change as well as an important O₃ precursor. The principal source of both NH₃ and CH₄ is the agricultural sector.

In contrast, emissions of SO₂ fell significantly from 2005, with a decrease of 76%. Major reductions were also seen for BC and NO_x, with falls of 43% and 36% respectively.

Figure 2 shows the trend in total emissions of heavy metals and BaP in the EU-27, indexed as a percentage of their value in the reference year 2005 and set against EU‑27 GDP as a percentage of the 2005 value. Emissions of nickel and arsenic fell by more than 50%, while emissions of mercury, lead and cadmium fell by 45%, 44% and 33% respectively. Emissions of BaP decreased the least (-18%).

The EEA briefing on the EU reporting status against National Emissions reduction Commitments Directive presents progress towards reducing emissions of key air pollutants regulated under EU legislation both at EU and Member State level. Looking forward, further action is required by all Member States if they are to meet future emission reduction commitments under the NEC Directive.

During the period 2005-2019, emissions showed a significant absolute decoupling from economic activity, which is desirable for both environmental protection and productivity gains. Absolute decoupling implies that a variable remains stable or decreases, while the growth rate of the economic driving force increases. Both Figures 1 and 2 show a reduction in EU-27 air pollutant emissions and an increase in EU-27 GDP. This implies that there are fewer emissions of key air pollutants for each unit of GDP produced per year. The greatest decoupling is seen for SO₂, followed by NO_x, BC, CO, NMVOCs and certain metals (nickel, arsenic lead, mercury). A decoupling of emissions from economic activity may be due to a combination of factors, such as increased regulation and policy implementation, fuel switching, technological improvements and improvements in energy or process efficiencies. The increase in the EU’s consumption of goods produced outside the EU also plays a role in the economic activity and emission trends.

Main Sources of Air Pollutants in 2019

The economic sectors that are the upstream sources of air emissions vary by pollutant. Figure 3 shows the contribution of the main source sectors to EU-27 emissions of key air pollutants in 2019.

• For particulate matter, the primary source of both PM₁₀ and PM_2.5 was energy consumption in the residential, commercial and institutional sectors, responsible for 40% and 53% of emissions respectively. The manufacturing and extractive industry and road transport were also significant sources for both pollutants, while agriculture was an important source of PM₁₀.
• The agriculture sector was the principal source of NH₃, responsible for 94% of emissions.
• The agriculture sector also contributed more than half of all CH₄ emissions. The waste sector was the second-largest source of CH₄.
• The road transport sector was the main source of NO_x emissions, responsible for 39% of emissions.
• Energy consumption in the residential, commercial and institutional sectors is the main source of CO and BC emissions.
• The manufacturing and extractive industry sector was the main source of NMVOC emissions, responsible for 47% of emissions. Agriculture was the second-largest contributor.
• Energy supply was the principal source of SO₂ emissions, with the manufacturing and extractive industry being the second-largest contributor.

Figure 4 shows the contribution of the main source sectors to EU-27 emissions of heavy metals and BaP in 2019.

• The manufacturing and extractive industry sector was the principal source of all heavy metal emissions, except nickel, responsible for 63% of lead, 55% of cadmium, 44% of mercury, and 36% of arsenic emissions.
• For arsenic and mercury the energy supply sector was the second-largest source of emissions, responsible for 35% and 40% respectively. The waste sector also contributed 15% of arsenic emissions.
• For lead, the second-largest source of emissions was road transport, at 16% of emissions, followed by the residential, commercial and institutional sector at 11% of emissions.
• For cadmium, after the manufacturing and extractive industry sector (55%), the residential, commercial and institutional, and energy supply sectors were important sources, responsible for 20% and 14% respectively.
• The energy supply sector was the main source of nickel emissions, responsible for 41% of emissions, with the manufacturing and extractive industry sector and non-road transport sector contributing 28% and 19% of emissions respectively.
• The residential, commercial and institutional sector was the primary source of BaP emissions, responsible for 87%.

“over the last two decades, a significant improvement in air quality has been seen across Europe”

Relationship Between Emissions and Concentrations of Key Air Pollutants

The assessment of the relationship between the estimated emissions of key air pollutants and their concentrations in ambient air, as measured at air quality monitoring stations, covers the EU-27 as well as Iceland, North Macedonia, Norway, Switzerland and the United Kingdom. Over the last two decades, a significant improvement in air quality has been seen across Europe. For the period 2005-2019, average concentrations of key pollutants in urban areas fell by:

• 27% for NO₂
• 61% for SO₂
• 37% for PM₁₀

For PM_2.5 average urban concentrations fell by 38% over the period 2008-2017.

O₃ concentrations are measured in terms of both long-term concentrations and short-term high peak concentrations. In contrast to the trend seen for other key pollutants, long-term average concentrations of O₃ in urban areas increased by 9% in the period 2005-2019, although peak concentrations decreased by 3%.

When comparing emission trends with concentration trends for air pollutants, differences are observed. Concentrations are primarily driven by anthropogenic emissions, estimated to be behind 90% of the trends in concentrations of NO₂ and PM₁₀ (ETC/ATNI 2020). However, concentrations are also affected by meteorological conditions, and, for certain pollutants, the contribution made by natural sources, long-range transport and concentrations of precursor gases in the atmosphere.

Regarding particulate matter, over the period 2008 to 2019, annual mean concentrations of PM_2.5 decreased by between 30% and 40%, depending on the type of monitoring station. Over the same period, primary emissions of PM_2.5 fell by 29%. A similar downward trend was seen for annual mean concentrations of PM₁₀ over the period 2005 to 2019, while emissions of primary PM₁₀ fell by 27% (ETC/ATNI, forthcoming). As such, concentrations of particulate matter fell at a slightly faster rate than anthropogenic emissions of particulate matter. This can be attributed to the falls in concentrations of precursor gases that drive the formation of secondary particulate matter, namely SO_x, NO_x and NH₃ (ETC/ATNI, 2019).

Weather conditions also influence concentrations of particulate matter. After accounting for the impact of meteorology, concentrations of PM_2.5 fell by between 24% and 34% from 2008 to 2019, depending on the type and location of monitoring station. For PM₁₀, from 2005 to 2019 concentrations fell by between 31% and 36%. These estimates align more closely with the falls in emissions and confirm that emissions reductions were the primary factor driving the trend in air quality concentrations of both PM_2.5 and PM₁₀ (ETC/ATNI, forthcoming).

For NO₂, from 2005 to 2019, annual mean concentrations at background stations fell by 30%, while emissions of NO_x (a mixture of NO₂ and nitrogen monoxide (NO)) declined more significantly (-45%) (ETC/ATNI, forthcoming). The difference may be linked to uncertainties in the emission estimates reported by countries, as well as possible relative increases in the amount of NO₂ formed as a result of the reaction between the NO component of NO_x and O₃ an increase that may be caused by the changing ratios over time of precursor pollutants in emissions from certain sources.

Ground-level O₃ is formed from chemical reactions in the presence of sunlight, following emissions of precursor gases, mainly NO_x, NMVOCs, CO and CH₄. As mentioned above, long-term average concentrations of O₃ increased slightly from 2005 to 2019, with the highest increases seen at traffic monitoring stations in urban areas. Trends in emissions of precursors drives the trend in long-term concentrations of O₃ across all countries (ETC/ATNI, 2020).

For the period 2005-2019, peak concentrations of O₃ were found to have decreased by between 2% and 5% at background sites (ETC/ATNI, forthcoming). In rural areas, where O₃ concentrations are usually highest, a decrease in peak concentrations was seen. Peak ozone concentrations vary significantly by year, with highs driven by hot weather conditions, as seen in 2003, 2015 and 2018. Such meteorological conditions were found to significantly counteract the benefits of reducing emissions of O₃ precursors in some countries (ETC/ATNI, 2020). When discounting the effects of meteorology, the decline in O₃ concentrations occurred during the period 2005 to 2010, with concentrations then stabilising up until 2019 (ETC/ATNI, forthcoming). Regarding SO₂ from 2005 to 2019 annual mean concentrations fell by between 55% and 70%, depending on the station type. This is broadly consistent with the reported fall in emissions of 75% over the same period.