Disparities in Global Air Quality: Analysis of PM2.5 Concentrations Across Six Regions of the Globe

Globally, the leading cause of outdoor air pollution is ambient particulate matter smaller than 2.5 microns (PM2.5). It is an environmental health risk that is associated with 4.2 million premature deaths annually. Understanding differences in the geographical distribution of PM2.5 can inform more efficient and equitable policymaking and resource allocation as part of global responses to air pollution. Using open-source data from the WHO 2016 Air Quality Database, we extracted and analyzed variables covering the annual mean concentrations of PM2.5 across six geographic areas of the globe – Africa (AFR), Europe (EUR), The Americas (AMR), South-East Asian Region (SEAR), Western Pacific Region (WPR), and the Eastern Mediterranean Region (EMR). We compared the PM2.5 concentrations using the Kruskal-Wallis test followed by Dunn’s post hoc estimation with Sidak adjustment. The data included 47(24.5%) AFR countries, 51(26.6%) EUR, 27(14.1%) WPR, 11(5.7%) SEAR, 35(18.2%) AMR, and 21(10.9%) EMR countries. Two EUR countries, Estonia and Sweden, recorded the lowest annual PM2.5 of 5.73µg/m³, while Niger, an AFR country, recorded the highest of 93.18µg/m³. At regional aggregate, WPR had the lowest median PM2.5 concentration (10.95µg/m³), followed by EUR (14.04µg/m³), AMR (20.5µg/m³), SEAR (33.15µg/m³), AFR (40.81µg/m³), and EMR (43.8µg/m³); these differences were statistically significant per the Kruskal-Wallis test (χ2 = 104.097; p = 0.0001) at the 95% confidence level. Dunn’s pairwise comparison revealed a 2-way split – PM2.5 concentrations for the EUR-WPR-AMR trio had non-significant pairwise comparisons but were significantly different from the AFR-SEAR-EMR trio which also had non-significant pairwise comparisons. There are significantly large disparities in average outdoor air quality across the different geographical regions, as proxied by PM2.5. Generally, developing countries have higher PM2.5 levels with the most polluted country being over 16 times worse off compared to the least polluted. To achieve the UN Sustainable Development Goal (SDG) targets for PM2.5 (SDG Indicator 11.6.2), national and regional level responses must account for the underlying causes of the disproportionate pollution and potential health impacts within the crucial debate on climate equity, to make human cities and settlements more resilient, safe, and sustainable (SDG 11).