Exceedance of air quality limit values in urban areas (CSI 004) - Assessment published Oct 2013
Air pollution (Primary topic)
Typology: Descriptive indicator (Type A - What is happening to the environment and to humans?)
- CSI 004
Key policy question: What progress is being made in reducing concentrations of air pollutants in urban areas to below the limit values (for sulphur dioxide, nitrogen dioxide and particulate matter) or the target values (for ozone) defined in air quality legislation?
Particulate Matter (PM10)
In the period 2001-2011, 20-44 % of the urban population in EU-27 was potentially exposed to ambient concentrations of particulate matter (PM10) in excess of the EU limit value set for the protection of human health (50 microgram/m3 daily mean not to be exceeded more than 35 days a calendar year); (Figure 1).
Nitrogen dioxide (NO2)
In the period 2001-2011, 5-23 % of the urban population in EU-27 was potentially exposed to ambient nitrogen dioxide (NO2) concentrations above the EU limit value set for the protection of human health (40 microgram NO2/m3 annual mean). There was a slight downwards trend over the period (Figure 1).
In the period 2001-2011, 14-65 % of the urban population in EU-27 was exposed to ambient ozone concentrations exceeding the EU target value set for the protection of human health (120 microgram O3/m3 daily maximum 8-hourly average, not to be exceeded more than 25 times a calendar year, averaged over three years and to be achieved where possible by 2010). The 65 % of the urban population exposed to ambient ozone concentrations over the EU target value was recorded in 2003, which was the record year. There was no discernible trend over the period (Figure 1).
Sulphur dioxide (SO2)
In the period 2001-2011, the fraction of the urban population in EU-27 that is potentially exposed to ambient concentrations of sulphur dioxide in excess of the EU limit value set for the protection of human health (125 microgram SO2/m3 daily mean not to be exceeded more than three days a year), decreased to less than 1 %, and as such the EU limit value set is close to being met everywhere in the urban background (Figure 1).
Particulate Matter (PM10)
PM10 in the atmosphere results from direct emissions (primary PM10) and from emissions of particulate precursors (nitrogen oxides, sulphur dioxide, ammonia and organic compounds) which are partly transformed into particles by chemical reactions in the atmosphere (secondary PM10).
For the period before 2001, the number of monitoring stations in some areas of EU-27 was relatively small. Since 2001 the coverage improved, firstly in the EU-15 country and since 2005 in the whole EU-27. Notwithstanding these limitations, it is clear that a significant proportion of the urban population (20-44 %) was exposed to concentrations of particulate matter in excess of the EU limit values set for the protection of human health during the period 2001-2011 (Figure 2).
The observed time series is short and the natural meteorological variability is large therefore it is not possible to draw firm conclusions on a possible trend in the data. Preliminary analyses indicate a downward change in the highest daily mean PM10 values although for the majority of stations the observed change is statistically not significant. In Figure 3, the 36th highest daily average is shown; compliance with the short-term limit value is assured when this value is below 50 microgram/m3. The variations in Figures 2 and 3 are partly caused by the variable number of cities or stations. When a consistent set of stations are used in a trend analysis; a small decrease is observed, especially since 2006 ().
Emissions of the gaseous precursors for secondary PM are being reduced by enforcement of EU legislation (e.g. NEC Directive) and UNECE LRTAP Convention protocols (United Nations Economic Commission for Europe, Convention on Long-range Transboundary Air Pollution). Abatement techniques to reduce precursor emissions often also reduce the primary particulate emissions. Other measures (e.g. traffic measures from Auto-Oil-I and II Programme, waste incineration directive, road traffic introduction of EURO standards and the Directive on industrial emissions) should further reduce PM10 emissions.
Despite the likely future reductions in emissions, PM10 concentrations are expected to remain well above the daily limit values in most of the urban areas in the near future.
In total 25 of the 27 EU-27 Member States, which are included in the Urban Audit have submitted information on PM10 concentrations at 'urban background' and 'sub-urban background' stations to the air quality database AirBase. Data for Greece and Malta are not included due to missing availability of operational urban and sub-urban background monitoring stations in the Urban Audit cities.
Nitrogen dioxide (NO2)
The main source of nitrogen oxides emissions to the air is the use of fossil fuels; road transport, power plants and industrial boilers account for more than 95% of European emissions.
In the period 2001-2011, the fraction of urban population living in cities with urban background concentrations in excess of the 40 microgram NO2/m3 limit value gradually decreased from 23 to 5 % (Figure 4). However, it is expected that also in cities where the urban background concentration is below the limit value, limit values are exceeded at hot spots, in particular in locations with high density of traffic. The decrease in recent years is mainly caused by the fact that in a few very large cities (London, Manchester, Madrid and Barcelona) the averaged background concentrations dropped below the limit value.
Enforcement of current EU legislation (Directive on industrial emissions, Auto-Oil programmes, the National Emissions Ceilings Directive (NECD)) and LRTAP Convention protocols have resulted in a reduction of nitrogen oxides (NOx) emissions. Until now this reduction has not been fully reflected in the annual averages of NO2 concentrations observed at the urban background stations. Figure 5 shows a prevailingly decreasing trend.
Peak nitrogen dioxide levels occur often in busy streets in cities where road traffic is the main source. Since the introduction of catalytic converters at the end of the 1980s, their growing penetration in the car fleet and other measures have contributed to reducing emissions (). The result has been a downward trend in the number of exceedances of the hourly limit value (). Peak levels depend on meteorological conditions; year-to-year fluctuations are 10 to 20 % or more.
In total 24 of the EU-27 Member States, which are included in the Urban Audit have submitted information on nitrogen dioxide concentrations at 'urban background' and 'sub-urban background' stations to the air quality database 'AirBase'. Data for Cyprus, Greece and Malta are not included due to missing availability of operational urban and sub-urban background monitoring stations in the Urban Audit cities.
Although reductions in emissions of ozone precursors appear to have led to lower peak concentrations of ozone in the troposphere, the current target level is frequently exceeded for a substantial part of the urban population of the EU-27 Member States. Figure 6 shows estimates for 2011, indicating that 89 % of the urban population experienced exceedance of the 120 microgram O3/m3 level during at least one day (the long-term objective for protection of human health), while about 14 % of the urban population was exposed to concentrations above the target level of 120 microgram O3/m3 level during more than 25 days. The target level was exceeded over a wide area (and much more than just 25 days).
Figure 7 suggest that the 26th highest daily maximum 8-hour average value (if this parameter drops below 120 microgram O3/m3, there is compliance with the target value) does not show any trend. This statement has to be treated with caution. Firstly because the inter-annual variability of the weather has a large impact on the ozone levels and secondly because the number of stations is not stable over the full period.
The reductions in ozone precursor emissions that should result from enforcement of the NEC Directive and the LRTAP Convention protocols are unlikely to reduce ozone concentrations to below the current target value and long-term objective over the whole of the EU-27 Member State area.
In total 24 of the EU-27 Member States, which are included in the Urban Audit have submitted information on ozone concentrations at 'urban background' and 'sub-urban background' stations to the air quality database 'AirBase'. Data for Cyprus, Greece and Malta is not included due to missing availability of operational urban and sub-urban background monitoring stations in the Urban Audit cities.
Sulphur dioxide (SO2)
Sulphur in coal and oil and in mineral ores is the main source of sulphur dioxide in the atmosphere. Up to 1960s, coal and oil combustion in large and small sources was the typical situation in many European cities, resulting in very high sulphur dioxide and PM concentrations. Since then, the combustion of sulphur-containing fuels have largely been removed from urban and other populated areas, first in western Europe and now also increasingly in most central and eastern European countries. Large point sources (power plants and industries), remain the predominate source of sulphur emissions. These sources, usually with high stacks, are most often located away from population centres.
As a result of the important reductions in sulphur dioxide emissions achieved in the last decades, the fraction of the urban population exposed to concentrations above the EU limit value has been reduced to less than 1 % (Figure 8). The reduction in sulphur dioxide peak concentrations is more clearly seen in the trend of the 4th highest daily sulphur dioxide concentration on urban stations in the period 2001-2011 (Figure 9). Compliance with the limit value for the daily mean is assured when the 4th highest concentration is below 125 microgram SO2/m3. A further decline in concentrations is expected in the coming years. However, peak concentrations above EU limit values still occur, especially close to sources and in cities. Peak levels strongly depend on meteorological conditions; year-to-year fluctuations are 10-20 % or more.
Several factors have contributed to the decrease in sulphur dioxide concentrations. The first (1985) and the second (1994) sulphur protocol under the UNECE LRTAP Convention, together with EC limit values set in the previous Air Quality Directive (89/427/EEC amending 80/779/EEC) have resulted in major European emission reductions and correspondingly decreasing ambient concentrations. Political changes in the beginning of 1990s in the central and eastern European countries connected with economic restructuring, decline of heavy industry and adoption of abatement measures on large point sources has contributed to decreasing winter smog episodes in central and western European countries. Policies and measures such as the Directive on industrial emissions, standards regulating emissions from transport, the National Emission Ceilings Directive, and the reductions agreed under LRTAP Convention are expected to further reduce sulphur dioxide levels. Programmes for the reduction of sulphur emission from ships are also underway.
In total 23 of the EU-27 Member States, which are included in the Urban Audit have submitted information on sulphur dioxide concentrations at 'urban background' and 'sub-urban background' stations and the data is available in the air quality database ‘AirBase’. Data for Cyprus, Denmark, Greece and Malta is not included due to missing availability of operational urban and sub-urban background monitoring stations in the Urban Audit cities. However, the majority of the information on sulphur dioxide concentrations results from stations in EU-15 Member States. The limit values tend to be more widely exceeded in the Central and Eastern European countries ().
() ETC/ACM Technical Paper 2011/1. European exchange of monitoring information and state of the air quality in 2009: http://acm.eionet.europa.eu/reports/ETCACM_TP_2011_1_EoI_AQ_meta_info2009
() The EMEP Centre on Emission Inventories and Projections (CEIP): http://www.ceip.at/
() EEA Report No 2/2007. Air pollution in Europe 1990-2004: http://reports.eea.europa.eu/eea_report_2007_2/en
() See AirBase ‘Produced maps and graphs’: http://www.eea.europa.eu/data-and-maps/figures/airbase-exchange-of-information-3/so2-2008-concentration/fancybox.html
AirBase - The European air quality database
provided by European Environment Agency (EEA)
Gisco - Urban Audit 2004
provided by Statistical Office of the European Union (Eurostat)
More information about this indicator
See this indicator specification for more details.
Contacts and ownership
EEA Contact InfoMichel Houssiau
EEA Management Plan2013 1.0.2 (note: EEA internal system)
Frequency of updates
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This briefing is part of the EEA's report The European Environment - State and Outlook 2015. The EEA is an official agency of the EU, tasked with providing information on Europe’s environment.
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