Atmospheric Measurement Techniques

Abstract. We present car Multi-Axis (MAX-) DOAS ob-servations of tropospheric NO2 carried out on circles around the cities of Mannheim and Ludwigshafen (Germany) on 24 August 2006. Together with information on wind speed and direction, the total emissions of the encircled source(s) are quantified from these measurements. In contrast to recent similar studies based on zenith scattered sun light (elevation angle of 90◦), we use a MAX-DOAS instrument mounted on a car, which observes scattered sun light under differ-ent elevation angles (here 45◦, and 90◦). Compared to sim-ple zenith sky observations, MAX-DOAS observations have higher sensitivity and reduced uncertainty, and avoid sys-tematic offsets in the determination of the vertically inte-grated trace gas concentration. The determination of the ab-solute value of the integrated tropospheric trace gas concen