[Low emission zones in Germany : A reliable measure for keeping current air quality standards?]

Low Emission Zones (LEZs) were implemented as a measure for improving the quality of ambient air. As of February 2018, 58 LEZs were in operation in Germany; however they differ significantly, especially regarding their size.The effectiveness of LEZs has been investigated by dispersion modelling as well as by analysis of PM₁₀ (particles which pass through a size-selective inlet with a 50 % efficiency cut-off at 10 μm aerodynamic diameter) and nitrogen dioxide (NO₂) measurement values. Recent studies show a clear trend. In sufficiently large and strictly regulated LEZs, a reduction of PM₁₀ concentration between 5 and 10% can be shown, and at some traffic sites above 10%. The current (currently valid) limit values for PM₁₀ were introduced in 2005, mainly due to the adverse health effects of fine particles on respiratory and cardiovascular morbidity and mortality. The most health-relevant PM₁₀ particle fraction consists mainly of traffic-related particles and here especially of diesel soot particles. Therefore, the German regulations for LEZs promote using diesel particulate filters in diesel cars.Unfortunately, the evaluation of the LEZ effects is mostly restricted to PM₁₀, a particle fraction containing only a comparatively small portion of highly toxic exhaust-related particles. The analysis of air pollutants that are more traffic specific (such as elemental carbon, ultrafine particles, PM_2.5 [particles which pass through a size-selective inlet with a 50 % efficiency cut-off at 10 μm aerodynamic diameter]) would be more adequate. For "powerful" LEZs, more pronounced reductions of such pollutants have clearly been shown. This also means that the benefit of LEZs on human health is by far greater than is presently visible from routine measurements of PM₁₀.Since the stickers for LEZs are in fact meant to reduce particulate matter, it is not surprising that the introduction of LEZs has not resulted in a demonstrable reduction in NO₂ concentrations.