Long-range PM_2.5 pollution and health impacts from the 2023 Canadian wildfires

Smoke from extreme wildfires in Canada adversely affected air quality in many regions in 2023^1,2. Here we use satellite observations, machine learning and a chemical transport model to quantify global and regional PM_2.5 (particulate matter less than 2.5 μm in diameter) exposure and human health impacts related to the 2023 Canadian wildfires. We find that the fires increased annual PM_2.5 exposure worldwide by 0.17 μg m^-3 (95% confidence interval, 0.09-0.26 μg m^-3). North America had the largest increase in annual mean exposure (1.08 μg m^-3; 0.82-1.34 μg m^-3), but there were also increases in Europe (0.41 μg m^-3; 0.32-0.50 μg m^-3) owing to long-range transport. Annual mean PM_2.5 exposure in Canada increased by 3.82 μg m^-3 (3.00-4.64 μg m^-3). In the USA, the contribution of the Canadian fires to increased PM_2.5 was 1.49 μg m^-3 (1.22-1.77 μg m^-3), four times as large as the contribution from the 2023 wildfires originating in the USA. We find that 354 million (277-421 million) people in North America and Europe were exposed to daily PM_2.5 air pollution caused by Canadian wildfires in 2023. We estimate that 5,400 (3,400-7,400) acute deaths in North America and 64,300 (37,800-90,900) chronic deaths in North America and Europe were attributable to PM_2.5 exposure to the 2023 Canadian wildfires. Our results highlight the far-reaching PM_2.5 pollution and health burden that large wildfires can have in a single year.