Breathing Cities: Air Quality, Population Exposure, and Sustainability Implications in 33 European Capitals

This study investigates long-term urban air quality and population-level exposure in 33 European capital cities between 2010 and 2024. Using over 3.5 million hourly observations retrieved from official monitoring networks, city-level Air Quality Index (AQI) values were calculated and analyzed for exceedance frequency, seasonal dynamics, and spatial disparities. To account for public health relevance and sustainability implications, the analysis incorporated population-weighted exposure indicators reflecting both pollution severity and urban demographic scale. The results reveal substantial differences in air quality across the continent: cities such as Oslo and Reykjavik consistently maintain low AQI levels, while Sarajevo, Lisboa, and Madrid experience frequent exceedances. Notably, Paris shows the highest cumulative population exposure despite moderate pollution intensity, highlighting how urban density amplifies public health burdens. The use of harmonized AQI and exposure-adjusted metrics enables standardized comparisons across cities and supports sustainability-oriented urban planning. By quantifying unequal exposure burdens across Europe’s capitals, this study contributes to the evidence base for Sustainable Development Goal 11, emphasizing the need for data-informed air quality policies that address both environmental risks and population vulnerability.