Estimating real driving emissions from multi-axis differential optical absorption spectroscopy (MAX-DOAS) measurements at the A60 motorway near Mainz, Germany

摘要

In urban areas, road traffic is a dominant source of nitrogen oxides ( NO x = NO + NO 2 ). Although the emissions from individual vehicles are regulated by the European emission standards, real driving emissions often exceed these limits. In this study, two multi-axis differential optical absorption spectroscopy (MAX-DOAS) instruments on opposite sides of the motorway were used to measure the NO 2 absorption caused by road traffic at the A60 motorway close to Mainz, Germany. In combination with wind data, the total NO x emissions for the occurring traffic volume can be estimated. Hereto, the ozone-dependent photochemical equilibrium between NO and NO 2 is considered. We show that for 10?May 2019 the measured emissions exceed the maximum expected emissions calculated from the European emission standards for standardised test cycles by a factor of 11±7 . One major advantage of the method used here is that MAX-DOAS measurements are very sensitive to the integrated NO 2 concentration close to the surface. Thus, all emitted NO 2 molecules are detected independently from their altitude, and therefore the whole emission plume originating from the nearby motorway is captured, which is a key advantage compared to other approaches such as in situ measurements.