NO₂ lidar profile measurements for satellite interpretation and validation

Abstract

Satellite instruments are efficient detectors of air pollutants such as NO 2 . However, the interpretation of satellite retrievals is not a trivial matter. We describe a novel instrument, the RIVM NO 2 mobile lidar, to measure tropospheric NO 2 profiles for the interpretation and validation of satellite data. During the DANDELIONS campaign in 2006 we obtained an extensive collection of lidar NO 2 profiles, coinciding with OMI and SCIAMACHY overpasses. On clear days and early mornings a comparison between lidar and in situ measurements showed excellent agreement. At other times the in situ monitors with molybdenum converters suffered from NO y interference. The lidar NO 2 profiles indicated a well‐mixed boundary layer, with high NO 2 concentrations in the boundary layer and concentrations above not differing significantly from zero. The boundary layer concentrations spanned a wide range, which likely depends on the wind directions and on the intensity of local (rush hour) traffic which varies with the day of the week. Large diurnal differences were mainly driven by the height of the boundary layer, although direct photolysis or photochemical processes also contribute. Small‐scale temporal and spatial variations in the NO 2 concentrations of the order of 20–50% were measured, probably indicative of small‐scale eddies. A preliminary comparison between satellite and lidar data shows that the satellite data tend to overestimate the amount of NO 2 in the troposphere compared to the lidar data.