Health-based air-quality guidelines
- WHO air-quality guidelines inform national standards
- Air-quality guideline comparisons require matching averaging periods
- Interim air-quality targets guide progressive exposure reduction
- Some particulate pollutants have qualitative good-practice guidance
- WHO 2021 PM2.5 guidance distinguishes annual and daily exposure
- The 2021 WHO update changed pollutant guidelines unevenly
- Single-pollutant guidelines do not quantify every mixture exposure
- Particle size affects penetration into lungs and bloodstream