With the help of the research aircraft Geophysica, European scientists took to searching for the cause of the widening hole in the ozone layer. Geophysica is a retrofit of the stratospheric research shuttle Myasishchev M55 and reaches heights of 22 km. A laser diode spectrometer is on board to simultaneously determine the H2O and HNO3 contents of the cirrus clouds.
The tests were supervised by P. Mazzinghi of the Istituto Nazionale di Ottica Applicata (INOA), Florence. The cirrus clouds that were analyzed (PSC = polar stratospheric clouds) have a temperature of –70 °C to –90 °C and are located between 15 and 28 km above the earth’s surface.
It is generally assumed that such aerosol particles as HNO3/H2SO4/H2O and HNO3-nH2O, which are present in these cirrus clouds, are partially responsible for the depletion of the ozone layer.
On board the Geophysica, gas concentration measurements have to be done not only selectively but also with high sensitivity and speed. This is truly an area predestined for the application of laser diode spectroscopy!
For example, when measuring the concentration of HNO3 within a 2.5 sec. time period using a single-mode lead salt laser at 1,719.3 cm-1, 4 ppb HNO3 were detected within the absorption cell. A corresponding concentration of 0.1 ppb HNO3 can be calculated for the area outside of the absorption cell.
For a measurement campaign in Aracatuba, Brazil, in February 2005 the measurement system was refitted with a lead salt laser suitable for CO absorption.
The findings depict the inhomogeneity of the stratosphere. Substructures commonly 4 km in size were found. In addition, an inverted correlation between carbon monoxide and ozone content was discovered. This could be shown with the help of another independent measurement system when spots with a lower concentration of ozone also showed increased concentrations of CO.
This evidence is a new discovery in climate research!
Reference:
G. Toci, P. Mazzinghi, B. Miele and L. Stefanutti: “An airborne diode laser spectrometer for the simultaneous measurement of H2O and HNO3 content of stratospehric cirrus clouds” Opt. & Las. Eng. 37, pp. 459-480 (2002).
