Estimating real driving emissions from MAX-DOAS measurements at the A60 motorway near Mainz

Nitrogen oxides (NO_x = NO + NO₂) have a direct and indirect impact on human health. Therefore, the World Health Organization recommends limiting the concentration of nitrogen dioxide (NO₂) in the atmosphere. Nevertheless, these limits are regularly exceeded. Especially, fossil fuel combustion from road traffic is a major contributor to the emission of NO_x.

Multi Axis-Differential Optical Absorption Spectroscopy (MAX-DOAS) is able to measure trace gases in the lower troposphere. Here, this remote sensing method was used to measure NO_x emissions at a highly frequented motorway. Two MAX-DOAS instruments were set up on both sides of the A60 motorway close to Mainz, Germany. The parallel viewing direction allows measuring the background signal at the upwind side and the background plus traffic emissions on the downwind side. Together with the effective wind speed perpendicular to the motorway, it is thus possible to retrieve the total traffic emissions. Compared to the expected emissions calculated from the European emission standards, the derived emissions of NO_x are by a factor 7±4 higher.

In this study, first measurement results are presented and the method is evaluated with regard to the practicability and error margin.