European Air Quality Index

The European Air Quality Index allows users to understand more about air quality where they live, work or travel. Displaying up-to-date information for Europe, users can gain insights into the air quality in individual countries, regions and cities.

The Index is based on concentration values for up to five key pollutants:

• particulate matter (PM₁₀);
• fine particulate matter (PM_2.5);
• nitrogen dioxide (NO₂);
• ozone (O₃);
• sulphur dioxide (SO₂).

It reflects the potential impact of air quality on health, driven by the pollutant for which concentrations are poorest due to associated health impacts.

The index is defined hourly and it consists of two independent layers: the stations layer and the modelled layer.

The station layer shows information for more than 3.500 air quality monitoring stations across Europe, using a combination of Up-To-Date (UTD) data reported by EEA member countries (data is not formally verified by countries) and a forecast of the air quality level following a downscaling of the forecast provided by the Copernicus Atmospheric Monitoring Service (CAMS).

The user can filter the stations by country and by station type. Stations are classified in relation to the predominant emission sources: traffic, industry and background (where the station’s main pollution source is dominated neither by traffic nor by industry). The available viewing options include all stations, traffic stations only, or non-traffic stations (i.e. industrial and background stations).

The modelled layer shows information for every single 1x1 km grid in Europe using a downscaling of the forecast provided by CAMS. This allows getting information also for locations without any monitoring stations nearby.

By default, the Air Quality Index depicts the situation 3 hours ago. Additionally, users can select any hour within the past 48 hours and also view forecast values for the next 48 hours.

European Union legislation sets air quality standardsfor both short-term (hourly or daily) and long-term (annual) air quality levels. The Index indicates the short-term (hourly) air quality situation. It does not reflect the long-term (annual) air quality situation, which may differ significantly (information on this can be found at the quality statistics | European Environment Agency's home page).

The air quality index is not a tool for checking compliance with air quality standards and cannot be used for this purpose.

1. Methodology

Concentration values for up to five key pollutants determine the index level that reflects air quality at each monitoring station in the station layer, or grid in the modelled layer. The index corresponds to the poorest level for any of the five pollutants, according to the table shown below.

 a. Stations layer

The Index uses Up-To-Date (UTD) air quality data officially reported every hour by EEA member countries, complemented (where necessary) by modelled air quality data obtained by downscaling the forecast from the CAMS ,i.e. if there are gaps in the UTD data, it is filled with the downscaled CAMS modelling.

Circles and dots on the map represent the locations of the air quality monitoring stations. The colours reflect the air quality index category at the given hour at that specific station according to the colour coding presented in the table below.

Averaging time for pollutants

To determine the AQI level, hourly concentrations of all five pollutants (PM_2.5, PM₁₀, NO₂, O₃, SO₂) are used.

Determining the index for traffic stations

When determining the index for traffic stations data from all available pollutants are used. However, the station is painted in full colour only when data is available for NO₂ and PM (either PM_2.5, PM₁₀ or both), otherwise the station is painted semi-transparent.

Determining the index for industrial and background stations

Similarly, at industrial and background stations, the index is determined for all stations but only those stations with data for at least the three pollutants NO₂, O₃ and PM (either PM_2.5, PM₁₀ or both) are painted in full colour, i.e. If they don’t have data for all three pollutants, the station is painted semi-transparent.

Stations missing data for certain pollutants

Stations not measuring all necessary pollutants to determine an overall station index are depicted as semi-transparent grey circles, indicating that the index is not determined with the minimum range of pollutants. These include stations that do not report data for all pollutants (or for which missing data cannot be gap-filled with modelled data). However, at there stations, the index is calculted internally for each measuerd pollutat individually. In the event, that the individual pollutant index is poor or worse, then the index colour is used at station level painted semi-transparent.

Small grey dots indicate active stations for which no data have been reported to allow the index to be determined. This might be because measurements are done manually with samplers or Up-To-Date transmission of data has not been established with EEA.

Missing data and gap filling

When data is not reported for a given hour, values are approximated, or 'gap-filled' using a downscaling of CAMS modelled air quality data. In such cases, it is marked with an asterisk in the pollutant timeline of the “Show details” view.

The method used for gap-filling depends on the pollutant.

• For NO₂, PM_2.5 and PM₁₀ a so called Difference method is used.
• For O₃ a Multiplicative method is used.
• No gap filling is performed for SO₂

Difference method: The value is approximated by taking the downscaled CAMS modelled value and adding or subtracting a correction difference. This correction is the average difference between previously measured values and the downscaled CAMS modelled value for the same hour for at least three of the four previous days.

Multiplicative method: The value is approximated by taking the downscaled CAMS modelled value, and applying a correction factor. This correction is the average ratio between the previously measured values and the downscaled CAMS modelled values for the same hour for at least three of the four previous days.

In cases where there are no measured values for the same hour over three of the four previous days, the AQI for the given pollutant is not determined.

Forecast index

Forecast values for the following 48 hours are shown as transparent circles. Circles are coloured as grey if the minimum number of required pollutants, depending on the type of station, could not be forecasted and the forecast index is good, fair or moderate.

To calculate the forecast values for the following 48 hours, CAMS modelled air quality data are downscaled and corrected using the gap-filling methods described above. No forecast values are provided for SO₂.

 b. Model layer

In this case there are no missing values, since a model is used and it pvoidesprovides results for every single 1x1km grid in the covered territory. The downscaled CAMS model is used for every hour, and the previous 48 hours together with the forecasted next 48 hours are presented.

2. Bands of concentrations and index levels

The AQI bands that determine the category thresholds are linked to health impacts, specifically to the risk factor of mortality due to short-term exposure.

The first two bands (Good and Fair) are set based on the World Health Organization Air Quality Guidelines (AQG, published by WHO in 2021) on long-term and short-term exposure, For SO₂, that does not have a long-term AQG level defined, the annual limit value in the revised Ambient Air Quality Directive (EU 2024/2881) was used instead.

The higher pollution bands (Moderate, Poor, Very Poor, Extremely Poor) were defined first for PM_2.5 considering the WHO interim targets and then for the rest of pollutants by estimating equivalent health risks to those for PM_2.5.

The Very Poor category for O₃ was adjusted to align with the EU information threshold, ensuring better public communication.

Other pollutant bands were rounded to match EU alert and information levels.

3. Health messages

The index bands are complemented by health-related messages that provide recommendations for both the general population and sensitive populations. The latter includes both adults and children with respiratory problems and adults with heart conditions.

4. Additional information

 a. Station layer

When clicking on a station , a pop-up window appears with the following additional information:

1. The name of the station and the air quality index at that station and hour.

2. The Index level at the given station.

3. A “Show details” option, with a summary of the station information; the air quality index and the associated health advice for the general population and sensitive populations; links to information on air pollution for the country where the station is located and to the webpage of the administration in charge of reporting the concentrations for that station; and two graphs, a pie- chart and a horizontal pie-chart.

The values indicated when hovering over the horizontal pie -chart show the hourly AQ Index, the hourly concentrations for all pollutants measured at the station or gap-filled over the last 7 days. An asterisk next to a value indicates that the value has been gap-filled.

The pie -chart indicates the number of days that fell under each Index band over the past 365 days, with the highest hourly index level recorded on a given day determining the daily index classification.

4. A “View station location” option, that provides the location of the station using © Google Maps.

 b. Modelled layer

When clicking on any point of the modelled layer, similar information to the one for stations appears for the grid to which the points belong to, although without the pie chart and the “View location” option.

Further information

The European Environment Agency publishes a range of information on air quality:

• Air pollution web page
• Air quality live: Up-to-date air quality measurement
• Key air quality statistics for the main air pollutants: map viewer
• Air quality status report
• Air pollution country profiles

The European Air Quality Index was developed jointly by the European Commission’s Directorate General for Environment and the European Environment Agency to inform citizens and public authorities about the recent air quality status across Europe.

Circles and dots on the station layer represent the locations of air quality monitoring stations. Similarly, coloured grids in the modelled layer represent squares sized 1x1km. The colour corresponds to the air quality index at the given hour at that station or grid.

Note that this hourly concentration may be quite differ to the annual average (see additional information under “About the European Air Quality Index)

Measurements of up to five key pollutants supported by modelled data determine the index level that describes the current air quality situation at each monitoring station or grid. The index corresponds to the poorest level for any of five pollutants according to the following scheme.

For the stations layer, the colour scheme is provided to give information on the status of the air quality at each station. Colours at the stations are either full or semi-transparent:

1. Full colour: the minimum number of pollutants required needed to calculate the index are met (see “About the European Air Quality Index” for details).
2. Semi-transparent colour: the minimum pollutant requirements for calculating the index are not met. The circle appears grey unless the available subset of pollutants indicates poor or worse air quality, in which case the corresponding index colour is shown.
3. Forecast values: Always displayed as semi-transparent. The index colour is shown if the forecast meets the minimum pollutant requirements, or if the forecasted index is poor or worse. If the minimum requirement is not met and the forecast indicates moderate or better air quality, the circle appears grey.

The grey dots indicate stations for which: no data has been reported nor could be gap-filled (using modelled data) to allow the index to be calculated.

For the map layer, colours are always solid as there are no missing data for any pollutant.

The graphs presented under “Show details” when clicking on a station or grid on the maps follows the same colour scheme as the station and gird. When hovering over the horizontal pie chart, the displayed concentrations correspond to:

• The hourly concentrations for all pollutants (PM₁₀, PM_2.5, NO₂, O₃ and SO₂)

For stations, an asterisk next to a value indicates that the value has been gap-filled (see details under “About the European Air Quality Index”).

The pie chart (only available for stations) indicates the number of days for each index category for the past 365 days (the highest hourly index level in a day determines the daily index category considered).

Details on the methodology to calculate the AQ Index can be found by clicking on “About the European Air Quality Index”.