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Richard White


Atmospheric sulfur dioxide data became available in 1982 during and after the eruption of El Chichon, when the Total Ozone Mapping Spectrometer, TOMS, received increased absorption in the shortest wavelength channels of the instrument. TOMS was designed to map the daily global total ozone field. The increased absorption was later determined to be due to sulfur dioxide because it is a gaseous volcanic substituent that has corresponding absorption to that seen in the TOMS data. Currently there is no way to develop an algorithm that will accurately subtract the effects of sulfur dioxide from the TOMS data in order to obtain the correct ozone amounts because the temperature dependence of sulfur dioxide absorption cross sections is unknown.

The experimental design to find the temperature dependence involves getting the ultra violet absorption spectra of sulfur dioxide in the wavelength region of 290-340 nm at 298 K, 210K and at least one temperature in between. There is very little low temperature data currently available, so the data is very important to develop an accurate model and algorithm.

The most important factor in the temperature dependence is the affect temperature has on the population of rotational energy levels. At room temperature molecules are able to occupy levels other than ground state. As the temperature is dropped, however, the higher energy levels become less populated and the ground level becomes more populated according to the Boltzmann distribution. The values of cross sections were observed to increase with temperature if they corresponded to a transition that was originated from a ground energy level and to decrease with temperature if the transition originated from a higher energy level.

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