In metropolitan areas throughout Europe maximum permissible values of nitrogen oxide are consistently breached. It has been a challenge to determine how much each polluter contributes to the emission output. Until now emission levels were mainly calculated by collecting emission data at laboratory testing facilities and subsequently extrapolating them in models. However, the amount of pollutant emissions that vehicles emit on a daily basis depends on numerous factors, for example on individual driving behavior. The recent Diesel scandal showed, for example, that measurements at engine test stands based on the New European Driving Cycle (NEDC) or similar emission testing procedures can be highly uncertain for predicting actual environmental impacts. A large number of new studies have recently been published suggesting that emission levels from test stands have to be adjusted upwards.
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