Birmingham Clean Air Zone (CAZ) is an area of central Birmingham, England where traffic is restricted to reduce air pollution. It became the third UK Clean Air Zone, after London and Bath, when it launched on 1 June 2021. A study of the zone’s effectiveness, published in 2023, found mixed results, with "modest, but significant reductions" in nitrogen dioxide but "no detectable impact in the concentrations of fine particles... the air pollutant with greatest health effects".