Exceedance of air quality limit values in urban areas (CSI 004) - Assessment published Dec 2008
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 1997-2006, 18-50% of the urban population was potentially exposed to ambient air 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 be exceeded more than 35 days a calendar year). There was no discernible trend over the period (Figure 1).
- Nitrogen dioxide (NO2)
In the period 1997-2006, 18-42% of the urban population was potentially exposed to ambient air 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).
- Ozone (O3)
In the period 1997-2006, 14-61% of the urban population in Europe 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). The 61% 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 1997-2006, the fraction of the urban population in EEA-32 member countries that is potentially exposed to ambient air 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 (Figure 1).
Percentage of urban population resident in areas where pollutant concentrations are higher than selected limit/target values, EEA member countries, 1997-2006
Note: Rationale for selection of pollutant and corresponding limit/target values for CSI 004 is given in the justification for indicator selection
Percentage of population resident in urban areas potentially exposed to PM10 concentration levels exceeding the daily limit value, EEA member countries, 1997-2006
Note: For years before 1997 representative monitoring data is not available
36th highest 24-hour PM10 concentration averaged through available urban background stations, EEA member countries, 1997-2006
Percentage of population resident in urban areas potentially exposed to NO2 concentration levels exceeding the annual limit value, EEA member countries, 1997-2006
Note: Over the years 1997-2006 the total population, for which exposure estimates are made, increased from 54 to 105 million people due to an increasing number of monitoring stations reporting air quality data
Annual mean NO2 concentration averaged through available urban background stations, EEA member countries, 1997-2006
Percentage of population resident in urban areas potentially exposed to O3 concentration levels over the long-term objective for protection of human health, EEA member countries, 1997-2006
Note: Over the years 1997-2006 the total population for which exposure estimates are made, increases from 49 to 104 million people due to an increasing number of monitoring station reporting under the Exchange of Information Decision
26th highest maximum daily 8-hour O3 concentration averaged through available urban background stations, EEA member countries, 1997-2006
Percentage of population resident in urban areas potentially exposed to SO2 concentration levels exceeding the daily limit value, EEA member countries, 1997-2006
Note: 1: The limit value is 125 µg SO2/m3 as a daily mean, not to be exceeded more than three days in a year
4th highest 24-hour SO2 concentration averaged through available urban background stations, EEA member countries, 1997-2006
- Particulate Matter (PM10)
PM10 in the atmosphere can result from direct emissions (primary PM10) or 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).
Monitoring of PM10 has only started recently and available data before 1997 is not representative for Europe. For the period 1997-2006, the number of monitoring stations in some areas of Europe was still relatively small and results may not be representative for all parts of Europe (Buijsman et al., 2004). Notwithstanding these limitations, it is clear that a significant proportion of the urban population (18-50%) was exposed to concentrations of particulate matter in excess of the EU limit values set for the protection of human health (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.
Emissions of the gaseous precursors for secondary PM are being reduced by enforcement of EU legislation 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) 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.
- 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 1997-2006, 18-42% of the urban population lives in cities with urban background concentrations in excess of the 40 microgram NO2/m3 limit value (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.
Enforcement of current EU legislation (Large Combustion Plant and IPPC Directive, Auto-Oil programme, 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 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 (-25% since 1980 in the EU-15) (1). The result has been a downward trend in the number of exceedances of the hourly limit value (2). Peak levels depend on meteorological conditions; year-to-year fluctuations are 10 to 20 % or more.
In total 25 of the EEA member countries 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'.
- Ozone (O3)
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 EEA member countries. Figure 6 shows estimates for 2006, indicating that 98% of the urban population experienced exceedance of the 120 microgram O3/m3 level (the long-term objective for protection of human health), while about 47% of the urban population was exposed to concentrations above the 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).
Several studies have shown that ozone peak values (e.g. given as 98-percentiles) have tended to decrease during the first half of the nineties. However, data available from AirBase for a consistent set of stations over the period 1996-2001 shows hardly any variation for the 26th highest daily maximum 8-hour average. Figure 7 shows this 26th highest value; if it drops below 120 microgram O3/m3, there is compliance with the target value. Furthermore, the annual mean ozone concentrations have increased, which is in agreement with several studies.
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 EEA area.
- 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 1997-2006 (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 Large Combustion Plants Directive, the IPPC Directive, 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 22 of the EEA-32 member countries 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. 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.
AirBase - The European air quality database
provided by European Environment Agency (EEA)
Gisco - Urban Audit 2004 (Eurostat)
provided by Eurostat - Statistical Office of the European Union (ESTAT)
More information about this indicator
See this indicator specification for more details.
Contacts and ownership
EEA Contact InfoMichel Houssiau
EEA Management Plan2010 (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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