Impact of low emission zones and local traffic policies on ambient air pollution concentrations

Background: Evaluations of the effectiveness of air pollution policy interventions are scarce. This study investigated air pollution at street level before and after implementation of local traffic policies including low emission zones (LEZ) directed at heavy duty vehicles (trucks) in five Dutch cities. Methods: Measurements of PM₁₀, PM_2.5, 'soot', NO₂, NO_x, and elemental composition of PM₁₀ and PM_2.5 were conducted simultaneously at eight streets, six urban background locations and four suburban background locations before (2008) and two years after implementation of the policies (2010). The four suburban locations were selected as control locations to account for generic air pollution trends and weather differences. Results: All pollutant concentrations were lower in 2010 than in 2008. For traffic-related pollutants including 'soot' and NO_x and elemental composition (Cr, Cu, Fe) the decrease did not differ significantly between the intervention locations and the suburban control locations. Only for PM_2.5 reductions were considerably larger at urban streets (30%) and urban background locations (27%) than at the matching suburban control locations (20%). In one urban street where traffic intensity was reduced with 50%, 'soot', NO_x and NO₂ concentrations were reduced substantially more (41, 36 and 25%) than at the corresponding suburban control location (22, 14 and 7%). Conclusion: With the exception of one urban street where traffic flows were drastically reduced, the local traffic policies including LEZ were too modest to produce significant decreases in traffic-related air pollution concentrations.