In 2025, annual average PM2.5 concentrations increased across Northern America, driven primarily by intense wildfire activity. Canada experienced a significant impact, reclaiming the highest regional pollution rank with a national the second most severe on record.80 The United States recorded a more moderate rise of 3%, reaching an annual The environmental consequences were acute in Flin Flon, Manitoba, the region's most polluted city in 2025. In late May, residents evacuated as fires originating in Saskatchewan crossed provincial borders; by June, Manitoba's PM2.5 Range of 2025 average PM2.5 (μg/m3) across regional cities Transboundary smoke also degraded air quality in U.S. states like Michigan and Minnesota, where levels nearly doubled in July relative to the previous year. Consequently, the proportion of regional cities meeting the WHO annual PM2.5 guideline fellfrom 29% in 2024 to 23% in 2025. Despite this historic wildfire activity, nearly one-third of regional cities demonstrated improved PM2.5 levels, suggesting that localied emission reductions or meteorological factors mitigated the impact in certain areas. quality monitoring network, accounting for 54% of the global monitoring stations and 45% of the total cities featured in the Report. In 2025, the number of monitored infrastructure is increasingly defined by the adoption of emerging technology; notably, low-cost sensors contributed 90% of the region's total data. The reliance on this hardware is even more pronounced at the municipal level, as 68% of the region's cities relied exclusively on 三 Burbank, CA, USA low-cost sensors for their air quality reporting. While these sensors have vastly increased the geographic reach of the network, they now represent the primary backbone of Northern America air quality data collection, providing the 三Astoria, OR, USA