Paris and London are Europe’s two megacities. Both experience poor air quality with systemic breaches of the NO2limit value. Policy initiatives have been taken to address this; some European-wide (e.g. Euro emission standards) and others local (e.g. Low Emission Zones). A study by Font et. al. evaluated trends in NOX, NO2 and particulate matter (PM10, PM2.5) for 2005 to 2016 in the background and roadside locations in Paris and London.
The study also looked at trends in traffic increments that were calculated in both cities to address their impact. Trends in traffic counts and the distribution in Euro standards for diesel vehicles were also evaluated.
Despite NO2 decreasing, at current rates, roads will need 20 years (Paris) and 193 years (London) to achieve the European Limit Value. Euro 5 light diesel vehicles were associated with a decrease in roadside PM10. An increase in motorcycles in London since 2010 contributed to the lack of a significant trend in PM2.5 roadside increment in 2010.
The success of current and future policies relies on the real-world emissions of new vehicles being less than the ones they replace. It is clear from comparing the traffic composition between the two cities that London’s low emission zones successfully replaced the intended vehicle types. However, it did not provide the expected impact on ambient pollutant concentrations, especially in NO2.
The responsibility for the transference of this success into ambient concentrations must, therefore, rest with the vehicle manufacturers that have previously engineered differences between type-approval tests and real-world emissions.
Euro 6/VI vehicles will include on-road testing as part of their standard emission testing and an improvement in ambient air quality in urban areas is therefore expected.
However, results from this study highlight that motorcycles may be causing hotspots of air pollution in European cities. A continued increase in the number of motorcycles and diesel car growth, especially light goods vehicles, could confound policies to reduce NO2 and PM concentrations.