Impact of the temporary closure of a major bridge on local air quality in two large German cities: an accountability study

Abstract

Despite recent achievements in reducing the contribution of road traffic to air pollution, agreed pollutant standards are exceeded frequently in large parts of Europe. Previous studies assessed the effectiveness of traffic interventions in improving local air quality. However, little research exists on the effect of closures of short road sections over longer periods. The multi-week maintenances on the Theodor Heuss Bridge, the main connection over the river Rhine between the German cities Mainz and Wiesbaden, offered the opportunity to investigate its effect on local air pollution. We measured ambient concentrations of major air pollutants and meteorological parameters at the Theodor Heuss Bridge before, during, and after its closure on 800 m in early 2020. We carried out time-series and closure-dependent evaluations of pollutant concentrations at the bridge accounting for wind direction. Furthermore, we performed regression analyses accounting for wind speed additionally. We compared the results with data from surrounding monitoring stations. We recorded higher concentrations at the Theodor Heuss Bridge compared to outside the closure, especially for particulate matter, nitric oxide, and black carbon. Only with wind from specific directions, we could detect reductions of concentrations during the closure for many pollutants as nitrogen dioxide (− 9.8%; 95% confidence interval: − 10.8– − 8.7%), but not for particulate matter. Since we found similar meteorology-dependent pollution reductions during the closure at both the bridge and the surrounding monitoring stations, we assume that regional meteorological factors overlaid a potential closure-related effect on local air quality. These factors must be accounted for in accountability studies on interventions focusing on short roads.

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