Street- and census-level NO<sub>2</sub> data for Barcelona with uncertainty and exceedance probability mapping.

Abstract

Air pollution is the leading environmental threat to public health. Despite their value in raising awareness and improving access to complex data, street-level air quality platforms remain scarce. Moreover, uncertainty in high-resolution air pollution estimates is rarely reported. This study presents six years (2019-2024) of nitrogen dioxide (NO₂) concentration data for Barcelona (Spain), along with spatial maps of associated uncertainty. Besides providing high-resolution annual estimates (25 m × 25 m), the database includes daily NO₂ concentrations at census-tract level, enabling temporal assessments with full spatial coverage citywide for the first time. The incorporation of uncertainty estimates represents a milestone for open street-scale air quality data and supports applications in health research, urban planning, and regulatory compliance. Finally, exceedance probability maps are provided, aligned with daily and annual NO₂ thresholds defined by the European Air Quality Directives (2008/50/EC and 2024/2881) and 2021 WHO guidelines. The database is accessible through the uncertAIR platform , offering information to citizens, policymakers, and scientists in Barcelona, while serving as a reference for worldwide open data platforms reporting uncertainty.