Exceedance of air quality limit values in urban areas (version 1)

Assessment versions

Published (reviewed and quality assured)

• No published assessments

Rationale

Justification for indicator selection

This indicator of the exposure of urban populations to air pollution focuses on sulphur dioxide, particulate matter (PM), nitrogen oxides and ground-level ozone. Sulphur dioxide (SO₂) is directly toxic to humans, its main action being on the respiratory functions. Indirectly, it can affect human health as it is converted to sulphuric acid and sulphate in the form of fine particulate matter.

Epidemiological studies have reported statistical significant associations between short-term, and especially long-term exposure to increased ambient PM concentrations and increased morbidity and (premature) mortality. PM levels that may be relevant to human health are commonly expressed in terms of PM₁₀ meaning particulate matter which passes through a size-selective inlet with a 50 % efficiency cut-off at 10 mg aerodynamic diameter. Health effect associations for the PM_2.5 fraction are even more clearly evident. Although the body of evidence concerning the health effects of PM is increasing rapidly, it is not yet possible to identify a concentration threshold below which health effects are not detectable. There is therefore no recommended WHO Air Quality Guideline for PM.

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).

Short-term exposure to nitrogen dioxide may result in airway and lung damage, decline in lung function, and increased responsiveness to allergens following acute exposure. Toxicology studies show that long-term exposure to nitrogen dioxide can induce irreversible changes in lung structure and function.

Exposure to high ozone concentration for periods of a few days can have adverse health effects, in particular inflammatory responses and reduction in lung function. Exposure to moderate ozone concentrations for longer periods may lead to a reduction in lung function in young children.

Scientific references

• Urban air quality CEC Structural Indicators
• SOx and NOx emission intensities OECD Key environmental indicators (KEI), 2004 Available indicator: SOx and NOx emission intensities Medium term indicator: Population exposure to air pollution
• Population exposure to air pollution, to noise OECD Core Environmental Indicators (CEI): Population exposure to air pollution, to noise L/M - Concentrations of air pollutants S
• Ambient concentrations of pollutants in urban areas UNCSD 1996
• Ambient Concentration of Air Pollutants in Urban Areas (methodology sheet) UNCSD 2001 www
• Air Ex1 Exposure to ambient air pollutants (urban) WHO EH indicators
• A.5 Quality of local ambient air (methodology sheet) Sustainability Profile - European Common Indicators www
• Local Air Quality Environment and Sustainability Profile for Oslo 2003 www
• WHO Air Quality Guidelines for Europe WHO Regional Publications, European Series, No. 91
• WHO air quality guidelines for particulate matter, ozone, nitrogen dioxide and sulphur dioxide. Global update 2005. Executive summary

Indicator definition

The indicator shows the fraction of the urban population that is potentially exposed to ambient air (1) concentrations of pollutants (2) in excess of the EU limit value set for the protection of human health.

The urban population considered is the total number of people living in cities with at least one monitoring station.

Exceedance of air quality limit values occurs when the concentration of air pollutants exceeds the limit values specified in the first Daughter Directive of the Air Quality Framework Directive for SO₂, PM₁₀ (3), NO₂ and the target values for O₃ as specified in the third Daughter Directive. Where there are multiple limit values (see section on Policy Targets), the indicator uses the most stringent case:

• Sulphur dioxide (SO₂): the daily limit value;
• Nitrogen dioxide (NO₂): the annual limit value;
• Particulate matter (PM₁₀): the annual limit value;
• Ozone (O₃): the short term objective.

(1) "Ambient air" shall mean outdoor air in the troposphere, excluding work places.

(2) "pollutant" shall mean any substance introduced directly or indirectly by man into the ambient air and likely to have harmful effects on human health and/or the environment as a whole.

(3) "PM₁₀" shall mean particulate matter which passes through a size-selective inlet with a 50 % efficiency cut-off at 10 mg aerodynamic diameter.

Units

Percentage of the urban population in Europe potentially exposed to ambient air concentrations (in mg/m³) of sulphur dioxide (SO₂), particulate matter (PM₁₀), nitrogen dioxide (NO₂) and ozone (O₃) in excess of the EU limit value set for the protection of human health.

Policy context and targets

Context description

This indicator is relevant information for the Clean Air for Europe (CAFE) programme.

A combined ozone and acidification abatement strategy has been developed by the Commission, resulting in a new Ozone Daughter Directive (2002/3/EC) and a National Emission Ceiling Directive (2001/81/EC). In this legislation, target values for ozone levels and for precursor emissions have been set.

For the protection of human health in the adopted Daughter Directive for sulphur dioxide, oxides of nitrogen, particulate matter and lead in ambient air (Council Directive 1999/30/EC).

Targets

EU limit values on concentrations of sulphur dioxide in ambient air

Two limit values have been set for the protection of human health. Both limit values have to be met by 1 January 2005.

• a limit value of 125 mg SO₂/m³ as an daily average, not to be exceeded more than three times a calendar year, has been set for the protection of human health in the adopted Daughter Directive for sulphur dioxide, oxides of nitrogen, particulate matter and lead in ambient air (Council Directive 1999/30/EC, Section I of Annex I).
• an hourly limit value for the protection of human health has been set at 350 mg SO₂/m³; this level may not be exceeded more than 24 times a calendar year.

EU limit values on concentrations of nitrogen dioxide in ambient air

Both limit values have to be met by 1 January 2010:

• In the first Daughter Directive (Council Directive 1999/30/EC, section 1 of Annex II) an annual mean limit value for nitrogen dioxide of 40 mg NO₂/m³ has been set for the protection of human health.
• In addition, an hourly limit value of 200 mg NO₂/m³ not to be exceeded more than 18 times a calendar year has been set.

EU limit values on concentrations of PM₁₀ in ambient air

Both  limit values should be met by 1 January 2005.

• a limit value for PM₁₀ of 50 mg/m³ (24 hour average, i.e. daily), not to be exceeded more than 35 times a calendar year is set for the protection of human health by the first Daughter Directive for sulphur dioxide, oxides of nitrogen, particulate matter and lead in ambient air (Council Directive 1999/30/EC, Annex III)
• an additional limit value of 40 mg/m³ as annual average has also been set.

EU target values on concentrations of ozone in ambient air

A combined ozone and acidification abatement strategy has been developed by the Commission, resulting in a new Ozone Daughter Directive (2002/3/EC) and a National Emission Ceiling Directive (2001/81/EC). In this legislation, target values for ozone levels and for precursor emissions have been set.

• The Ozone Daughter Directive sets a target value for the protection of human health of 120 mg O₃/m³ as maximum daily 8 hour mean, not to be exceeded more than 25 days per calendar year, averaged over three years. This target should be met in 2010 (short term objective).
• The Ozone Daughter Directive has also set a long-term objective of 120 mg O₃/m³ as a maximum daily 8 hour mean within a calendar year.

Related policy documents

• COM(2001) 245 final. The Clean Air for Europe (CAFE).
  The Clean Air for Europe (CAFE) Programme: Towards a Thematic Strategy for Air Quality COM(2001) 245 final
• Council Directive 96/62/EC of 27 September 1996
  Council Directive 96/62/EC of 27 September 1996 on ambient air quality assessment and management.
• Council Directive 1999/30/EC of 22 April 1999
  Council Directive 1999/30/EC of 22 April 1999 Relating to limit values for sulphur dioxide, nitrogen dioxide and oxides of nitrogen, particulate matter and lead in ambient air
• Directive 2001/81/EC, national emission ceilings
  Directive 2001/81/EC, on nation al emissions ceilings (NECD) for certain atmospheric pollutants. Emission reduction targets for the new EU10 Member States have been specified in the Treaty of Accession to the European Union 2003  [The Treaty of Accession 2003 of the Czech Republic, Estonia, Cyprus, Latvia, Lithuania, Hungary, Malta, Poland, Slovenia and Slovakia. AA2003/ACT/Annex II/en 2072] in order that they can comply with the NECD.
• Directive 2002/3/ EC...ozone in ambient air
  Directive 2002/3/ EC of the European Parliament and of the Council of 12 February 2002 relating to ozone in ambient air

Methodology

Methodology for indicator calculation

Sulphur dioxide (SO₂)

For each urban station, the number of days with a daily averaged concentration in excess of the limit value (125 mg SO₂/m³ as a daily mean) is calculated from the available hourly or daily values. Only time series with a data capture of at least 75 % per calendar year are used (that is with more than 274 valid daily values per calendar year). The selected urban stations include station types "urban background" and "sub-urban background". The number of exceedance days per city is obtained by averaging the results of all "urban" and "sub-urban background" stations.

Particulate matter (PM₁₀)

For each urban station the number of days with a daily mean concentration in excess of the limit value of 50 mg/m³ is calculated from the available hourly or daily values. The selected urban stations include station types "urban background" and "sub-urban background". Only time series with a data capture of at least 75% per calendar year are used (that is with more than 274 valid daily values per calendar year). The number of exceedance days per city, is obtained by averaging the results of all "urban" stations.

Nitrogen dioxide (NO₂)

The annual mean concentration in a city is calculated as the average of the annual mean value measured at all "urban background" and "sub-urban background" stations. Only time series with a data capture of at least 75% are used (that is with more than 274 valid daily values per calendar year).

Ozone (O₃)

The number of exceedance days is calculated for each "urban background" and "sub-urban background" stations. A city average number of exceedance days is obtained by averaging over all available "urban background" and "sub-urban background" stations. Only time series with a data capture of at least 75% are used (that is with more than 274 valid daily values per calendar year).

Methodology for gap filling

No gap-filling is applied for this indicator.

Methodology references

• European exchange of air quality monitoring meta information in 2002 Buijsman et al., 2004, ETC/ACC Technical Paper 2004/1

Data specifications

EEA data references

• AirBase - The European air quality database provided by European Environment Agency (EEA)

Data sources in latest figures

Uncertainties

Methodology uncertainty

The air quality data is officially submitted. It is assumed that data has been validated by the national data supplier. Station characteristics and representativeness is often insufficiently documented. The data is generally not representative for the total urban population in a country. Locally, the indicator is subject to year-to-year variations due to meteorological variability.

Data sets uncertainty

SO₂

Strength and weakness (at data level): The air quality data is officially submitted to the European Commission under the Exchange of Information Decision. It is assumed that the air quality data has been validated by the national data supplier. Station characteristics and representativeness is often insufficiently documented. Data coverage in non EEA-32 member countries needs improvement; data availability over the period 1980-1995 needs improvement.

Reliability, accuracy, robustness, uncertainty (at data level): The number of available data series varies considerably from year to year and is for the first part of the 1990s insufficient. The data is generally not representative for the total urban population in a country. Availability of data before 1990 is too low to include in the indicator; data for non EU Member States is largely missing before 1995. Locally, the indicator is subject to large year-to-year variations due to meteorological variability. When averaging over EEA member countries this meteorologically induced variation decreases in importance provided spatial data coverage is sufficient. Due to deficiencies in information on station characteristics, the selection of urban sites (i.e. of the type "urban background" and "sub-urban background") might not always result in a representative selection of polluted zones. As a consequence, the indicator may be biased (see at 6).The representativeness of the selection is different for different cities which reduces the comparability between cities. It is not possible at this stage to select a sufficiently large set of stations covering the entire time period since the stations with available data change from year to year.

PM₁₀

Strength and weakness (at data level): The air quality data is officially submitted to the European Commission under the Exchange of Information Decision. It is assumed that the national data supplier has validated the air quality data. Station characteristics and representativeness is often insufficiently documented. Geographical coverage and data availability needs improvement; as the majority of the stations is located in EU-15 Member States, the indicator will underexpose the situation in Accession Countries. Data has been considered both from monitoring with the reference method (gravimetry) and with other methods. It is not documented whether countries have applied correction factors for non-reference methods, and if so, which factors have been applied. Uncertainties associated with this lack of knowledge may be several tens of percents.

Reliability, accuracy, robustness, and uncertainty (at data level): The number of available data series varies considerably from year-to-year and is insufficient for the period before 1997. The data is generally not representative for the total urban population in a country. Locally, the indicator is subject to year-to-year variations due to meteorological variability. When averaging over EEA-32 this meteorologically induced variation decreases in importance provided spatial data coverage is sufficient. Due to deficiencies in information on station characteristics, the selection of urban (type "urban background" and "sub-urban background") sites might not always result in a representative selection of polluted areas. The indicator may be biased due to insufficient representative coverage of the pollution situation. The representativeness of the selection is likely to be different for different cities which reduces comparability.

NO₂

Strength and weakness (at data level): The air quality data is officially submitted to the European Commission under the Exchange of Information Decision. It is assumed that the air quality data has been validated by the national data supplier. Station characteristics and representativeness is often insufficiently documented. Data coverage in non EEA-32 member countries needs improvement; data availability over the period 1980-1995 needs improvement.

Reliability, accuracy, robustness, uncertainty (at data level): The number of available data series varies considerably from year-to-year and is for the first part of the 1990s insufficient. The data is generally not representative for the total urban population in a country. Availability of data before 1990 is too low to include in the indicator; data for non EU Member States is largely missing before 1995. When averaging over EEA-32 this meteorologically induced variation decreases in importance provided spatial data coverage is sufficient. Due to deficiencies in information on station characteristics, the selection of urban sites might not always result in a representative selection of polluted zones. As a consequence, the indicator may be biased. The representativeness of the selection is different for different cities which reduces the comparability between cities. It is not possible in this stage to select a sufficiently large set of stations covering the entire time period since the stations with available data change from year to year.

O₃

Strength and weakness (at data level): The air quality data is officially submitted to the European Commission under the Exchange of Information Decision. It is assumed that the air quality data has been validated by the national data supplier. Station characteristics and representativeness is often insufficiently documented. Data coverage in non EEA-32 member countries needs improvement; data availability over the period 1980-1995 needs improvement.

Reliability, accuracy, robustness, uncertainty (at data level): The number of available data series varies considerably from year to year and is for the first part of the 1990s insufficient. Yearly changes in indicator value may result from changes in monitoring density and/or selected cities which will influence the total monitored population. The indicator is subject to year-to-year fluctuations as it represents episodic conditions, and these depend on particular meteorological situations, the occurrence of which varies from year to year.

Data coverage in non EEA-32 member countries needs improvement; data availability over the period 1980-1995 needs improvement.

Rationale uncertainty

Work description

Resource needs

No resource needs have been specified

Status

Deadline