Abstract. A growing number of space-borne instruments measures nitrogen dioxide (NO₂) concentrations in the troposphere, but validation of these instruments is hampered by the lack of ground-based and in situ profile measurements.

The Royal Netherlands Meteorological Institute (KNMI) has developed a working NO₂ sonde. The sonde is attached to a small meteorological balloon and measures a tropospheric NO₂ profile. The NO₂ sonde has a vertical resolution of 5 m and a measurement range between 1 and 100 ppbv. The instrument is light in weight (0.7 kg), cheap (disposable), energy efficient and not harmful to the environment or the person who finds the package after use. The sonde uses the chemiluminescent reaction of NO₂ in an aqueous luminol solution. The NO₂-luminol reaction produces faint blue/purple light (at about 425 nm), which is detected by an array of silicon photodiodes. The luminol solution is optimised to be specific to NO₂.

An on-ground comparison with measurements from a Photolytic Analyser of The National Institute for Public Health and the Environment (RIVM) shows that both instruments measure similar NO₂ variations in ambient air.

During the Cabauw Intercomparison campaign of Nitrogen Dioxide measuring instruments (CINDI) in June/July 2009, six vertical profiles of NO₂ from the ground to a 5 km altitude were measured, which clearly show that the largest amount of NO₂ is measured in the boundary layer. The measured boundary layer heights of the NO₂ sonde are in good agreement with boundary layer heights determined by a LD40 Ceilometer at Cabauw.