1. European Commission’s Joint Research Centre (JRS)
https://ghsl.jrc.ec.europa.eu/
2. Air Quality in Europe—2020 Report
https://www.eea.europa.eu/publications/air-quality-in-europe-2020-report
3. WHO Air Quality Guidelines for Particulate Matter, Ozone, Nitrogen Dioxide and Sulfur Dioxide. Global Update 2005,2005
4. Legal Act of the European Union: Directive 2008/50/EC of the European Parliament and of the Council of 21 May 2008 on Ambient Air Quality and Cleaner Air for Europe OJ L 152; (BG, ES, CS, DA, DE, ET, EL, EN, FR, IT, LV, LT, HU, MT, NL, PL, PT, RO, SK, SL, FI, SV) Special edition in Croatian: 11 June 2008; 2008; Volume 29, Chapter 15, pp. 169–212
http://data.europa.eu/eli/dir/2008/50/oj
5. WHO Global Air Quality Guidelines: Particulate Matter (PM2.5 and PM10), Ozone, Nitrogen Dioxide, Sulfur Dioxide and Carbon Monoxide,2021