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Abstract
Nitrogen dioxide is an important pollutant in the atmosphere, it is toxic for living species, it forms photochemical tropospheric ozone, and acid rain. There is a growing number of space-borne instruments to measure the nitrogen dioxide concentration in the atmosphere, but calibration and validation of these instruments is hampered by a lack of ground based and in-situ measurements. We are currently developing a nitrogen dioxide sonde. The sonde is attached to a small meteorological balloon and will measure a NO2 profile from the ground to approximately 20 km altitude. We aim for a vertical resolution of 5 meters, and a sensitivity between 0.1 and 1 micrograms per cubic meter. The design of the instrument poses a number of challenges. The instrument should be light weight, cheap (disposable), energy efficient and not harmful to the environment or the person who finds the package after use. Therefore we can not make use of the popular molybdenum catalytic converter or a photomultiplier. Instead, we will use the chemilumenescent reaction of NO2 with an aqueous luminol solution. The NO2-luminol reaction produces a faint blue/purple light (425 nm), that will be detected by an array of photodiodes.
We exclude interfering compounds like ozone and sulpher dioxide by adding sodium sulphate. Interference from nitrogen monoxide and PAN (peroxy acetyl nitrate) is reduced by adding a small amount of a primary alcohol and triton x-100, respectively. The goal for the specificity of the luminol reaction to NO2 will be 90%. The efficiency of the NO2 luminol reaction depends on the PH of the solution. To avoid acidification of the system by carbon dioxide the chemicals are refreshed constantly.
By our knowledge this is the first and only NO2 sonde in the world. We will compare the performance of the NO2 sonde relative to the LIDAR and the MAX-DOAS at the CINDI (Cabauw Intercomparison Campaign of Nitrogen Dioxide measuring Instruments) campaign in June 2009.