Low-emission zones (LEZs) have been implemented widely in Europe to tackle air pollution sourced from vehicular emissions. We quantify the effectiveness of the world's largest LEZ—London's LEZ—in reducing its target pollutant, PM10. Using a difference-in-difference (DID) framework, we find that the least stringent phase I of London's LEZ induced a short-term increase in the roadside PM10 within the zone by about 14.8%, whereas the longer and more restrictive phase II significantly drove down the PM10 by 5.5%. We explore the underlying reasons behind the disparity in policy effect across stages. We show that upon the introduction of phase I, the traffic volume of targeted heavy goods vehicles (HGVs) and temporarily exempted light goods vehicles (LGVs) has substantially increased, outweighing the environmental effect of a higher proportion of greener vehicles. We provide possible behavioral explanations for this phenomenon.

低排放区（LEZs）已在欧洲广泛实施，以解决由车辆排放源引起的空气污染。我们量化了世界上最大的LEZ（伦敦的LEZ）在减少其目标污染物PM10方面的有效性。使用差异差异（DID）框架，我们发现伦敦LEZ最不严格的第一阶段导致该区域内路边PM10的短期增加约14.8％，而更长且更具限制性的第二阶段显着使PM10下降了5.5％。我们探索了跨阶段政策效果差异背后的根本原因。我们表明，在第一阶段推出后，目标重型货车（HGV）和临时豁免的轻型货车（LGV）的交通量已大大增加，超过了更高比例的绿色车辆对环境的影响。我们为这种现象提供了可能的行为解释。