Which data to deliver
Data transfer
Data format
City Pages

Join us is designed to accommodate air quality data from a multitude of cities and regions across Europe. You are welcome to join your city. The minimum information required is the year average concentration for the pollutants of main concern. If you want to participate in you only need to deliver the data according to a defined data format. All data processing, including the conversion of monitored values from µg/m3 into the Common Air Quality Index (CAQI), is done by the website. The complete procedure can be downloaded (pdf in english).

To become a member, please follow the instructions below and your air quality data will soon be available in an easy understandable and comparative way side by side with data from other European cities.
You must simply accept the conditions of license.

As a general rule cities are required to deliver two sets of data from monitoring sites representing the urban background and the roadside conditions.

Roadside situation:
NO2 and PM10 as the main pollutants; CO and PM2.5 as auxiliary pollutant (each in µg/m3)

Background situation:
NO2, PM10 and O3 as the main pollutants; CO, PM2.5 and SO2 as auxiliary pollutants (each in µg/m3)

Preferably data from a number of sites is requested, however it is up to each city what they want to contribute. The website will accept whatever a city submits as their data for the roadside and background situation and undertake any averaging calculations required.
Ideally the website accepts the above data on an hourly basis to show the dynamic behaviour of air pollution. However, to attract as many cities as possible and to accommodate different needs and capabilities, cities are free to enter the service on the following levels:

  • Mode 1: a City delivers hourly data in near real-time
  • Mode 2: a City has hourly data available but delivers data once per day or a city has only daily data (e.g. for PM10)
  • Mode 3: a City does not want to submit hourly data but wants to feed annual data*

Hourly and daily data
The File Transfer Protocol (FTP) has been chosen to transfer data to This protocol is easy to use, a remote directory can be treated just as a local directory and a large number of free and cross-platform FTP clients are available. Moreover, the latest FTP servers have improved security. Each city will have its personal directory, named with the city/region name, for uploading data using a Username and Password. The adoption of the FTP protocol assures that control is in the hands of the subscribing cities, who run the upload and don't have to allow external access to their databases.

Annual levels
Annual levels must be submited manually by participating cities using this form.

A common data format for delivering air quality data to has been developed and will be made available for subscribers to The data format uses the UTF-8 character set and consists basically of comma separated values (CSV). This type of data can be easily generated by any system and software. The data format will comprise an ID for the name of the station, its co-ordinates (longitude/latitude), information on the time and the concentration values as such. The details of the Common Data Format for data transfer are described in Annex 1 of the join procedures.

Beyond presentation and comparison of air quality data wants to provide relevant background information for each of the cities. Every city joining this website can present its specific situation according to a fixed format (text, graphs and pictures). Providing this information is not obligatory but it presents an opportunity to show your efforts in air quality management and include a link to your own website. It is meant to provide background information to the comparisons made on this website. A common layout defining which information should be published and the way this city information is presented can be seen at Participating cities page. In Annex 2 of the document with the join procedures (pdf in english) you receive some further guidance on the provision of your input to your City Page.

To join, please download the procedures and send a mail to You will receive a confirmation in short time.

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