The global air quality guidelines (AQG) provide recommendations for protecting human health in the form of AQG levels for PM₂.₅, PM₁₀, O₃, NO₂, SO₂ and CO. Additionally, they offer interim targets to guide reduction efforts towards achieving these levels and good practice statements on certain types of PM. Key features of these guidelines are: the use of new methods for evidence synthesis and guideline development; higher certainty in the evidence of health effects occurring at lower levels than previously understood; new AQG levels (i.e. peak season O₃ and 24-hour NO₂ and CO) and interim targets; and the good practice statements.