Application of Infrared and UV-Visible Remote Sensing Techniques for Studying the Stratosphere and for Estimating Antrophogenic Emissions

Abstract: Infrared and UV/visible broadband absorption techniques have been used in three applications related to environmental research and atmospheric science. The techniques are based on measuring the attenuation of light by the atmosphere in the infrared and UV/visible region, and since a very large number of species absorb light in these wavelength regions, the techniques studied allow the measurement of several species simultaneously.

Measurements of high resolution infrared solar spectra have been conducted during 1995 to 1998 at an observatory in Norway (60.2^oN, 10.75^oE). From the solar spectra, atmospheric columns of O₃ and the most abundant nitrogen, chlorine and fluorine species in the stratosphere have been retrieved, such as: HCl, ClONO₂, ClO, HNO₃, N₂O, HF and COF₂. In addition, height concentration profiles of HCl, O₃, HF, N₂O and CH₄ have been retrieved from the spectra. These were compared to several other techniques, indicating uncertainties of 10-20% at 20 km decreasing both upwards and downwards in altitude. Chlorine activation, i.e. conversion of the reservoir species HCl and ClONO₂ to ClO on ice particles in the stratosphere, could be quantified on several occasions during the measurement period. The measurements also indicated significant ozone depletion in the Arctic polar stratosphere of 1995.

In the second application a new method for quantitative estimation of fugitive emissions of hydrocarbons from petrochemical industries has been developed. Tracer gases are released on the location of the leakages, and then concentration measurements are conducted downwind, over a long atmospheric path, by infrared absorption technique. What is unique with the method is a new approach based on the correlation of the tracer and the source gas concentrations over time. The method has been used to measure diffuse emissions of ethylene and propylene at several industrial sites during 1994 to 1998. Sensitivity experiments and comparison with other techniques indicate the possibility of 20% accuracy for flux measurements of different volume and area sources with variable strengths 5-30 kg/h.

The third application studied concerns the development of a method for in situ measurements of environmental pollutants (NO, NO₂, SO₂ and NH₃) in flue gases by UV/visible absorption technique. The temperatures can be very high in the flue gases and, since the absorption line strengths are sensitive to the temperature, errors of up to 70% at 700K can be obtained if not taken into account. A laboratory study was conducted on this issue together with modeling of NO spectra. The concentrations of pollutants can be very high in flue gases why the absorption becomes nonlinear and yields errors of up to 30%. This has been studied in laboratory studies and modeling of NO spectra. The results from the laboratory studies were applied to compensate for the temperature and nonlinearity effects in real measurements.