The Barcelona Low Emission Zone: a post-implementation Health Impact Assessment from 2020 to 2022

Abstract Background A Low-Emission Zone (LEZ) is an area that restricts the use of polluting vehicles, aimed at cutting ambient air pollution (a major environmental health risk factor), thus improving public health. Barcelona introduced the Ring Roads LEZ (area = 95km2) in 2020, but its ex-post health impact remains unknown. Methods The LEZ effect on nitrogen dioxide (NO2) concentrations was estimated by the synthetic control method at six urban background and two traffic monitoring stations, accounting for pollution trends, COVID-19 restrictions, and meteorological effects from 2020 to 2022. NO2 reductions at the census-tract level (n = 1068) were modeled using linear regression, linking station-level NO2 reductions to changes in traffic volume from 2016 to 2021. We estimated these reductions as 2020-2022 averages and subtracted them from the baseline concentrations in 2019, obtaining net post-LEZ concentrations for each census tract. The impact on natural-cause mortality was assessed by the comparative risk assessment method, based on census-tract-level age- and sex-specific mortality data, using a prototype of healthiar (R package by the European-Union project BEST-COST). Results Among census tracts, the median NO2 concentration in 2019 was 38.0 µg/m3 (range: 16.3-46.6). The LEZ led to a median NO2 reduction of 5.3 µg/m3 (3.7-7.9), with an estimated median reduction in NO2 mortality burden of 24.4 deaths per year per 100,000 people aged over 20 (1.6-96.5). City-wide, this translates to 351 annual preventable deaths (95% CI: 223-464). The intervention was most effective in curbing the highest exposures (>40 µg/m3), shifting most of the population exposure to the 30-40 µg/m³ range. The estimated mortality reduction due to the LEZ is accordingly higher in areas with higher NO2 mortality burden at baseline (Spearman's ρ = 0.87). Conclusions Barcelona's LEZ reduced air pollution, with associated health benefits, particularly in areas with high NO2 concentrations at baseline. Key messages • The Barcelona low emission zone was effective at achieving and maintaining lower NO2 concentrations in ambient air. • The reduction in NO2 concentrations is associated with a reduction in mortality attributable to NO2, ranging from 223 to 464 annual deaths, thus providing health benefits to the population.