2011-03-01: The development of a nitrogen dioxide sonde
The sonde uses the chemiluminescent reaction of NO2 in an aqueous luminol solution. Chemiluminescent is an exothermic reaction, but instead of heat, light is emitted. 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 optimized to be specific to NO2 only.
The instrument is housed in a polystyrene (PS) foam box. PS is light in weight and a good insulator. The inside of the PS box is painted black, so ambient light is absorbed and can not disturb the measurement. To have an extra light barrier the instrument is placed in a black cardboard box. A radio transmitter (Vaisala RS92 radiosonde) is attached to the outside of the PS box, and sends the measurements back to the radio receiver.
Design of the instrument:
Figure 1 shows a schematic diagram of the design of the instrument.
During the Cabauw Intercomparison campaign of Nitrogen Dioxide measuring Instruments (CINDI) in June/July 2009, six NO2 sondes were launched and measured six NO2 profiles. Figure 2 shows the six profiles that were measured. The first NO2 sonde was launched on 18 June 2009, Figure 2a. This profile shows a maximum NO2 concentration around 930 m altitude and a clear top of the boundary layer at 2 km. Its vertical resolution is higher than that of the other sondes, because it had a smaller vertical velocity. The profile of 23 June 2009 (Figure 2b), shows at an altitude of 4.8 km a peak in NO2 concentration. This peak could have been caused by a layer of airplane exhaust. The profile of 30 June 2009 (Figure 2c) shows a second NO2 layer (1-3 km) above the boundary layer (0 – 1 km). The origin of this “second layer” could not be determined from meteorological measurements at Cabauw.
In December 2010, an article about the NO2 sonde is published in Atmospheric Measurement Techniques (AMT). More detailed information about the NO2 sonde can be found here.