Methods
Guideline development was initiated and overseen by a WHO steering
group. AQG recommendations and other guidance were informed by
systematic reviews and determined by the consensus decisions of a
guideline development group (GDG) comprised of subject matter experts in
the area of air quality and health. Evidence evaluation was guided by
the Grading of Recommendations Assessment, Development and Evaluation
approach.6 AQG levels were defined on the basis of
moderate or high certainty evidence supporting a link between a
pollutant and a particular health outcome over a long-term (annual mean
or highest six-month average) or short-term (24-hour) period. Thus,
long-term AQGs took precedence over short-term AQGs when both were
considered. Additional methodological details can be found in the
complete guideline text.
The AQG and interim target recommendations are summarized inTable 1 . Previously established WHO AQGs that are not addressed
in this update remain valid. Good practice statements for the management
of certain types of health risk-associated PM – black carbon/elemental
carbon (BC/EC), ultrafine particles (UFP), and sand and dust storms
(SDS) – are listed in Table 2 . Further discussion of the
rationale and complete citations for the recommendations can be found in
the guideline.