Air quality standards for the concentration of particulate matter 2.5, global descriptive analysis

OBJECTIVE: To compare ambient air quality standards for the mass concentration of aerosol particles smaller than approximately 2.5 μm (PM(2.5)) and exposure to these particles in national and regional jurisdictions worldwide. METHODS: We did a review of government documents and literature on air quality standards. We extracted and summarized the PM(2.5) concentration limits effective before July 2020, noting whether standards were enforced, voluntary or target. We compared averaging methods and permitted periods of time that standards may be exceeded. We made a descriptive analysis of PM(2.5) standards by population, total area and population density of jurisdictions. We also compared data on actual PM(2.5) air quality against the standards. FINDINGS: We obtained data on standards from 62 jurisdictions worldwide, including 58 countries. Of the world’s 136.06 million km(2) land under national jurisdictions, 71.70 million km(2) (52.7%) lack an official PM(2.5) air quality standard, and 3.17 billion people live in areas without a standard. The existing standards ranged from 8 to 75 µg/m(3), mostly higher than the World Health Organization guideline annual limit of < 10 µg/m(3). The weakest PM(2.5) standards were often exceeded, while the more stringent standards were often met. Several jurisdictions with the highest population density demonstrated compliance with relatively stringent standards. CONCLUSION: The metrics used in PM(2.5) ambient air quality standards should be harmonized worldwide to facilitate accurate assessment of risks associated with PM(2.5) exposure. Population density alone does not preclude stringent PM(2.5) standards. Modernization of standards can also include short-term standards to unmask PM(2.5) fluctuations in high-pollution areas.