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Exceedances of air quality objectives due to traffic

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Justification for indicator selection

This indicator of transport contribution to air quality focuses on particulate matter (PM10) and nitrogen dioxide (NO2). The negative impacts of these two pollutants on human health are outlined in CSI 004 and road transport is the largest or among the largest sources of emissions related to these pollutants. Especially in urban areas, where the majority of the European population lives and works, the contribution of road transport to the observed concentrations is especially high, leading to increased exposure levels to the two pollutants. It is therefore relevant to compare the concentrations observed at traffic stations (stations located close to road traffic emission sources which are often in the city centres) to those observed at background stations.

Scientific references:

  • No rationale references available

Indicator definition

The indicator compares concentrations at background stations to those at traffic stations. This comparison provides an estimate of the increased levels of air pollution that the population is exposed to when accessing areas with increased road traffic, as well as a measure of the impact of the technical and non-technical measures adopted to reduce the contribution of the road transport sector to the observed concentrations. 

The indicator makes use of the data submitted to Airbase. Data permitting, a pan-European coverage is attempted and the indicator focuses on selected station pairs (traffic and urban background stations) from capital cities across and where data in capital cities is not available the next largest city is chosen.

Values are presented for single monitoring stations that provide reliable time series data for the period 2000 to 2011.


Average yearly, average daily and average weekly variations of the concentrations at traffic and urban background stations (in micro g/m3).

Policy context and targets

Context description

This indicator is relevant information for the current European air quality legislation related to the setting of national emission targets (National Emission Ceiling Directive 2001/81/EC), the reduction of transport related emissions (discussed in detail in TERM 34) and the protection of human health from harmful air pollutant levels (Directives 1999/30/EC for sulphur dioxide, nitrogen dioxide and particulate matter and 2002/3/EC for ozone, both discussed in detail in CSI 004). The Directive on ambient air quality and cleaner for Europe (Directive 2008/50/EC) also sets target and limit values for PM2.5 (particulate matter which passes through s size-selective inlet with a 50% efficiency cut-off at 2.5 um aerodynamic diameter), since 2010.


EU limit values on concentrations of nitrogen dioxide in ambient air

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

  • In the 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.
  • An hourly limit value of 200 mg NO2/m3 not to be exceeded more than 18 times a calendar year has also been set.

EU limit values on concentrations of PM10 in ambient air

Both limit values had to 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 has been set in Council Directive 1999/30/EC (Annex III)
  • a limit value of 40 mg/m3 as annual average has also been set.


EU limit values on concentrations of other pollutants:

- sulphur dioxide

Two limit values have been set for the protection of human health. Both limit values had 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 1999/30/EC, Section I of Annex I.
  • an hourly limit value for the protection of human health has been set at 350 mg

- ozone 

A combined ozone and acidification abatement strategy has been developed by the European 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.
  • The Ozone Daughter Directive has also set a long-term objective of 120 mg O3/m3 as a maximum daily 8 hour average within a calendar year (not to be exceeded any day).

Related policy documents


Methodology for indicator calculation

Data submitted to Airbase has been used. The average diurnal variation was obtained by averaging each hour of the hourly data available at the selected measurement station. Average weekly variation was obtained by averaging the daily average for each day of the week (hourly or average daily data where used, depending on data availability) at the selected measurement station. Average yearly data was obtained from average hourly or average daily data, whichever was available at the selected measurement station (see data availability table for details). For all of the above, data gaps were not filled in.

Methodology for gap filling

No gap-filling is applied for this indicator, however the databases and spreadsheets used for the production of the indicator contain gap-filled values.

Methodology references

No methodology references available.

Data specifications

EEA data references

Data sources in latest figures


Methodology uncertainty

The air quality data is officially submitted data. It is assumed that data has been validated by the national data supplier. Station characteristics and representativeness is often insufficiently documented. The data is thought to be representative for the urban population in each city. Locally (at the city level) the indicator is subject to year-to-year variations due to meteorological variability.

Data sets uncertainty

Strengths and weaknesses (at data level): officially reported data by the countries to Airbase is used, however the data reported across countries varies in quantity. Also the station characterisation (urban background or traffic) is difficult to compare across countries. Reliability, accuracy, robustness, uncertainty (at data level): The uncertainties are discussed separately for each graph. The data quality cannot be commented upon, since it data reported by the individual countries, but data availability is sometimes low and does not allow for robust conclusions/intercomparisons (see data availability table for details). Main problem is the lack of data and not the actual quality of the data available.

Rationale uncertainty

No uncertainty has been specified

Further work

Short term work

Work specified here requires to be completed within 1 year from now.

Work description

Timeseries Countries should improve data availability in Airbase, in terms of the yearly coverage. A suggestion would be that for stations that have recently been included in Airbase, also the past data could be uploaded, if available. A continuous problem is that stations close down and therefore timeseries become redundant as new stations must be used. Pollutants In terms of the pollutant coverage, all countries should ensure that there is at least one station of each type in Airbase, for the largest urban agglomeration and measuring all “basic” pollutants such as NO x , CO, PM 10 , SO 2 . In this analysis NO 2 has been used instead of NO x due to the lack of available data. When looking at traffic contribution, it would be more appropriate to study NO x data, so improvement in this direction would also be necessary. Furthermore, as scientific evidence indicates that PM 2.5 form the largest part of the PM 10 measured at traffic stations, it should become obligatory for the member states to measure PM 2.5   in urban agglomerations, namely at traffic stations. The new Directive on ambient air quality and cleaner for Europe (Directive 2008/50/EC) sets target and limit values for PM 2.5 and is expected to increase the availability and submission of such data to Airbase, enabling its consideration in future indicator analysis. Other data Meteorological data is needed in order to estimate the meteorologically induced variation in the concentrations observed. Member States should be encouraged to submit such data to a relevant database, perhaps Airbase could be extended to include such information also, as it is always needed in an air quality analysis. Station information in Airbase It is not sufficient to just know the station type but rather it is necessary to understand the geometry of the area the station is located in and also where within the urban area (in relation to major roads and significant industrial sources) it is located. Such data is requested by Airbase, but following the EoI decision, it is not obligatory for the MS to deliver this data. It is important that countries submit this type of data, as this would greatly help with this type of analysis. Spatial coverage Based on measurements, spatial coverage of all EEA member countries is not possible. This can only be done with the assistance of models. In order to draw conclusions for the urban areas as a whole (and not station specific conclusions) using measurements only, adequate coverage in terms of number of stations is necessary. This is not the case for the urban areas at present. Other transport modes Based on available measurements, only road transport can be considered in this analysis.

Resource needs

No resource needs have been specified


In progress


2015/12/31 00:00:00 GMT+1

Long term work

Work specified here will require more than 1 year (from now) to be completed.

General metadata

Responsibility and ownership

EEA Contact Info

Cinzia Pastorello


European Environment Agency (EEA)


Indicator code
TERM 004
Version id: 1
Primary theme: Transport Transport


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Frequency of updates

Updates are scheduled once per year in October-December (Q4)


DPSIR: State
Typology: Descriptive indicator (Type A - What is happening to the environment and to humans?)

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