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High resolution diode laser carbon dioxide environmental monitor


To develop a new instrument for measuring atmospheric CO2 based on diode laser absorption spectroscopy.

Carbon dioxide is a very well known gas, and its importance for greenhouse effect is well established. All
around the world there is a network of measurement points (GAW, Global Atmospheric Watch of the World
Meteorological Organization) in order to measure its change in the local or in the global scale. In Italy the two
stations in this network are on the Cimone Mountain (owned by the Air Force) and at the Lampedusa Island
(belonging to ENEA). The Italian National Electricity Committee owns a further station at Plateau Rosa. In
Germany there are several stations belonging to the Umweltbundesamt and three other ones are in the area of
Garmish-Partenkirchen (Garmish-Partenkirchen itself, Wank Peak and Zugspitze). The knowledge of the exact
value of CO2 concentration in the atmosphere is fundamental for the determination of the actual contribution
of this gas to greenhouse effect and to give an estimation of the future trend. The average concentration of CO2
(referred to dry air) is about 350 ppm, and for an isolated station the range of variation is at most 345-375 ppm.
Higher values are obtained nearby woods, towns or plants. Moreover, the seas have a buffer effect on CO2.
A percentage in the range 20-50% of CO2 produced by burning fossil fuels is estimated to be absorbed by the
oceans. The uncertainty in this value is due to the lack of knowledge of the mechanism of exchange of CO2 at
the water surface. Performing CO2 measurement for climatological studies requires precise, fast and water
vapour insensitive instruments. The only kind of instrument presently used in this field is based on the
absorption of infrared radiation by carbon dioxide. Measurements are performed continuously and the output
values are sampled at intervals greater than the time necessary to completely change the air in the absorption
cell. This kind of instrument is widely used all over the world because it satisfies almost all the requirements
and there are practically no alternatives. The main problem of this type of device is stability. As a matter of
fact, during routine operation calibration is performed at intervals in the range 1-12 hours. A more stable
instrument would be preferable, in order to reduce the overall dimensions of the apparatus, the calibration gases
consumption and the time wasted during the calibrations.
The instrument to be developed would satisfy the following ideal requirements: Resolution 0.1 ppm; High
stability (ideally one day between two calibrations); Unaffected by water vapour; Possibility of remote operation;
Low power consumption; High repetition rate of the measurements (one measurement every few seconds). The
instrument is based on the latest technologies in the field of high resolution spectroscopy (FM technique with
DFB diode lasers) and would constitute a significant improvement in terms of performance, energy consumption,
size and ownership cost. Therefore this new instrument would result ideal for installation in remote sites such
as mountains.The experience gained in the development of this instrument will contribute to further
improve the know-how of the partners also in view of the possible future design of other high performance
environmental monitoring instruments.


T.R.I. Srl
Via Aldo Moro
24020 Scanzorosciate

Participants (2)

Ente per le Nuove Tecnologie, l'Energia e l'Ambiente (ENEA)
Via Enrico Fermi 27
00044 Frascati
Tullastr. 72
79108 München