Mortality impacts of air pollution and greenness: real-world and counterfactual exposure scenarios in seven Northern European cities

Background: Air pollution and greenness are important determinants of population health. Understanding their long-term impacts can inform integrated urban and environmental policies to reduce mortality and improve health. Objectives: To quantify both the real-world and potential impacts of two decades of changes in air pollution and greenness on all-cause mortality among adults aged 18-65 years in seven Northern European cities. Methods: We conducted a health impact assessment using cohort-derived exposure distributions from 16,404 adults in the Respiratory Health in Northern Europe (RHINE) study. Annual exposures to particulate matter (PM2.5, PM10), nitrogen dioxide (NO2), and greenness (Normalized Difference Vegetation Index, NDVI) were estimated at residential addresses for 1990-2010. Exposure changes were linked to all-cause mortality using established exposure-response functions to estimate population attributable fractions (PAFs). Additional analyses estimated potential health benefits under the 2021 WHO Air Quality Guidelines (AQGs) and enhanced greenness scenarios. Results: Between 1990 and 2010, exposures decreased on average by 3.0 μg/m3 for PM2.5, 4.4 μg/m3 for PM10, and 2.3 μg/m3 for NO2, while NDVI increased by 0.11. These changes corresponded to estimated PAF of 2.15% (95% CI: 1.83%-2.47%) for PM2.5, 2.53% (95% CI: 2.35%-2.72%) for PM10, 0.46% (95% CI: 0.41%-0.51%) for NO2, and 2.07% (95% CI: 1.88%-2.25%) for NDVI, representing the proportion of premature deaths prevented or delayed. Under counterfactual scenarios, alignment with the WHO AQGs would correspond to PAFs of 3.01% (95% CI: 2.58%-3.42%) for PM2.5, 1.56% (95% CI: 1.43%-1.69%) for PM10, and 1.59% (95% CI: 1.41%-1.77%) for NO2, while increasing greenness to the 75th percentile would correspond to 6.44% (95% CI: 5.74%-7.16%). Conclusion: Real-world environmental improvements were estimated to prevent or delay a measurable proportion of all-cause deaths among working-age adults. Larger benefits could be achieved under more ambitious air quality and urban greening targets. These findings support integrated environmental policies to enhance public health.