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| Titel |
The Development of a Nitrogen Dioxide Sonde |
| VerfasserIn |
Wesley Sluis, Marc Allaart, Ankie Piters, Lou Gast |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250038910
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| Zusammenfassung |
| 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 nitrogen dioxide
concentrations in the atmosphere, but validation of these instruments is hampered by 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 meter, and a
measurement range between 1 and 100 ppbv. The instrument is light in weight (±300
gram), cheap (disposable), energy efficient and not harmful to the environment or the
person who finds the package after use. Therefore the popular molybdenum catalytic
converter or a photomultiplier tube can not be used. Instead the sonde uses the
chemiluminescent reaction of NO2 in an aqueous luminol solution. The NO2– luminol
reaction produces a faint blue/purple light (± 425 nm), which is detected by an array of
silicon photodiodes.
The instrument is equipped with a reservoir filled with luminol solution. A small
piezoelectric diaphragm pump, pumps the luminol solution into a reaction vessel. A Teflon
air pump forces the ambient air into the reaction vessel. The NO2 in the ambient
air reacts with the luminol solution, and the emitted light is detected by an array
of silicon photodiodes which are mounted on the reaction vessel. The generated
current in the photodiodes is amplified and relayed to the ground by a Vaisala (RS92)
radiosonde.
The reaction vessel and the amplifiers are mounted in a tin can, to shield against
electrostatic and radio interference, and stray light. All the air tubes used for the instrument
are made of Teflon.
The luminol solution is optimised to be specific to NO2. Sodium sulphate, sodium EDTA
and Triton X-100 are added to the luminol solution to exclude ozone (O3) and PAN (peroxy
acetyl nitrate) interference. 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. Furthermore, treating the luminol solution with clean air for an
extended period before the measurement, makes the luminol / NO2 reaction more
efficient.
The NO2 sonde is compared to a NO2 in-situ monitor with bluelight converter (M200E,
BLC) of RIVM. Both instruments measure the same NO2 variations during a certain period
of time during the day.
During the Cabauw Intercomparison campaign of Nitrogen Dioxide measuring
Instruments (CINDI) in June/July 2009 we measured six vertical profiles of NO2 from the
ground to 5 km altitude. The NO2 sonde measurements will be compared with the Ozone
Monitoring Instrument (OMI) on the EOS-Aura satellite, and other in-situ measurements like
LIDAR and MAX Doas. |
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