Indoor air pollution estimates at a city-wide scale in Barcelona

Abstract

Urban air quality presents a significant global environmental challenge. In this context, understanding indoor and outdoor air quality levels is key to assessing population exposure better. Despite extensive research on modeling and monitoring air quality, studies that simultaneously model both remain limited. This study addresses this gap by combining Nitrogen Dioxide (NO2) outdoor levels from the CALIOPE-Urban air quality model with indoor-outdoor parametric relations. Bias-corrected NO2 concentration levels at the street scale are used. These NO2 levels are based on a kriging data-fusion method, merging monitoring station data and the CALIOPE-Urban dispersion model. Two parametric relations depending on building use are assessed for deriving indoor air quality levels: infiltration rates and indoor-outdoor ratios. Bias-corrected outdoor levels and the parametric relations are combined to obtain unprecedented city-wide maps containing indoor NO2 concentrations accounting for uncertainty quantification. Despite large confidence intervals in our results, the validation against observational data shows satisfactory model performance. Results reveal significant variations in indoor NO2 concentrations across different districts, with the highest levels observed in areas with heavy traffic such as the l’Eixample district. Specifically, in this area, 70% of homes have a probability of 50% or higher of exceeding the legal threshold of 40 μg/m³, posing considerable health risks for their inhabitants. This comprehensive approach refines the understanding of indoor and outdoor air quality dynamics in Barcelona, revealing NO2 pollution hotspots and enabling reliable and comprehensive air pollution exposure studies.