Munich's selective diesel vehicle ban and its impact on nitrogen dioxide concentrations: A quasi-experimental study

The current limit on NO₂ concentrations of 40 μg/m³, set by the European Union, has been regularly exceeded in Munich, Germany. This limit will likely be reduced towards the WHO recommended target of 10 μg/m3. Against this backdrop, the city implemented a selective diesel vehicle ban within the existing low-emission zone in February 2023, targeting Euro 4 and older diesel vehicles. Our study investigated the effect of Munich's selective diesel vehicle ban on NO₂ concentrations, focusing on the half-year period following its implementation.

Our study utilized a synthetic control approach (primary analysis) and a controlled interrupted time series approach (secondary analysis). These quasi-experimental methodologies create a 'counterfactual' no-intervention scenario, enabling comparison between observed and counterfactual scenarios to estimate an intervention effect. We employed historical controls, using routine data from multiple monitoring stations located within and outside the low-emission zone for 2014 to 2022, and considered possible confounders.

NO₂ concentrations within Munich's low-emission zone showed overall declining trends from August 2014 to July 2023. Effects of the selective diesel vehicle ban were small and wide confidence intervals indicate large uncertainty in the magnitude and direction of the effect. At Landshuter Allee, the average intervention effect was -2.67 μg/m³ (95 %-CI = [-12.72; 7.38]), at Stachus it was -2.74 μg/m³ (95 %-CI = [-9.91; 4.42]), and at Lothstrasse it was -1.03 μg/m³ (95 %-CI = [-7.75; 5.69]). The secondary analysis confirmed these findings, reinforcing uncertainty about the effect of the intervention.

Our study suggests that Munich's selective diesel vehicle ban had a limited effect on lowering NO₂ concentrations. Possible explanations include the ban's focus on Euro 4 and older diesel vehicles, many exemptions to the selective ban, and unclear enforcement. This highlights that comprehensive approaches and ongoing, well-designed monitoring and evaluation are crucial for addressing urban air pollution and protecting public health.