Wildfires were the primary factor. Record emissions from wildfires in Europe and Canada contributed roughly 1,380 megatonnes of carbon from biomass burning globally in 2025. Regions that had historically performed well on air quality saw levels slip precisely because wildfire smoke doesn't respect borders or planning assumptions. The data underscores a growing disparity in air quality: while 75 countries saw reductions in particulate matter, 54 others experienced increases.
Central and South Asia remained the most polluted region in the world, with 17 of the 20 most polluted cities globally concentrated there. Pakistan ranked as the most polluted country at 67.3 μg/m³, more than 13 times the WHO guideline. New Delhi recorded a capital city average of 82.2 μg/m³. In January alone, Hanoi residents faced conditions that were hazardous for nearly a third of all hours in the month.
One of the more significant findings in the report isn't about the pollution levels themselves. It's about the monitoring infrastructure that tracks them.
In March 2025, the U.S. State Department ended its global air quality monitoring program, which had provided primary data sources for cities across dozens of countries. According to reporting cited in the report, monitoring efforts were weakened in 44 countries, leaving six nations with no data coverage at all. Countries already underrepresented in global datasets, particularly across Africa and West Asia, lost one of their most reliable benchmarks.
For sustainability and ESG professionals at companies with global supply chains or international operations, this matters in a practical way. Environmental risk assessments, disclosure frameworks, and investor-facing climate reports increasingly depend on credible, location-specific air quality data. When that data disappears or becomes unreliable in markets where you operate, the gaps don't stay invisible. They surface in disclosure reviews and due diligence processes.
The picture isn't entirely negative. Brazil saw a 33% reduction in its annual average PM2.5 concentration. Bogotá won the prestigious Earthshot Prize for clean air improvements after cutting pollution 24% since 2018. Several Southeast Asian countries met WHO Interim Target 1 for the first time. Thailand's parliament unanimously passed a Clean Air Act in 2025.
Progress is possible. But as the report's executive summary puts it, air quality is a fragile asset rather than a fixed achievement. The 2025 data is a useful reminder that sustainability teams need to treat air quality monitoring as an ongoing operational concern, not a box checked at the start of a reporting cycle.
