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

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.

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.

We obtained data on standards from 62 jurisdictions worldwide, including 58 countries. Of the world's 136.06 million km² land under national jurisdictions, 71.70 million km² (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/m³, mostly higher than the World Health Organization guideline annual limit of < 10 µg/m³. 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.

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.