(5)In September 2021, the WHO updated its Air Quality Guidelines, based on a systematic review of the scientific evidence on health effects of air pollution. The updated WHO Air Quality Guidelines highlight new evidence about effects occurring at low levels of exposure to air pollution, and formulate lower air quality guideline levels for particulate matter (PM 10 and PM 2,5 ) and for nitrogen dioxide compared to previous guidelines. This Directive takes into account the latest scientific evidence, including the most up-to-date WHO Air Quality Guidelines.