Application of Passive DOAS using Scattered Sunlight for quantification of gas emissions from anthropogenic and volcanic sources

Doktorsavhandling, 2009

Monitoring of gas emissions from natural and anthropogenic sources is important due to the negative effects of these emissions on human health, atmospheric quality and ecosystems. Concern over air pollution has increased the need to develop measurement techniques suitable for gas flux determination. Differential Optical Absorption Spectroscopy (DOAS) is a method based on the interaction of light with matter. DOAS has been widely used during the past decades, is capable of quantifying several molecules simultaneously, provides results in real time with good time resolution and is non invasive, as well as precise and flexible to use in different conditions and environments. In this thesis, instruments based on scattered sunlight spectroscopy have been used to successfully quantify gas emissions from anthropogenic (refineries, power plants, chemical industries, urban areas) and volcanic sources during several field campaigns. The studied gas species were sulphur and nitrogen dioxides (SO2, NO2) mainly because of their negative effects on human health as well as oxidation capability, formation of sulphuric and nitric acids respectively and further dry or wet deposition; as well as formaldehyde (HCHO), which plays an important role in the chemistry of the troposphere. Results presented in this thesis demonstrate that the use of mobile and scanning mini-DOAS instruments are accurate for wind speed and plume height calculations as well as for quantification of SO2, NO2 and HCHO emissions. Calculated SO2 and NO2 emissions from Mexican refineries and power plants, conducted during field studies presented in this thesis, are in agreement with published inventories and indicate a significant reduction in emissions over recent years. Measurements conducted in the Houston-Galveston region in the United States show that SO2 and NO2 quantified emissions in some of the industrial areas were comparable with the reported values in the inventory, however slightly above the reported values. In addition HCHO has been identified in urban (Mexico City) and industrial (Houston, Texas) areas. The capability to continuously quantify gas emissions from volcanoes, using scanning mini-DOAS instruments, provides volcanic observatories with a new tool that allows them not only to react when facing a volcanic crisis but also to act proactively and in the best interest of the affected population. Quantified emissions from volcanic sources have been correlated to volcanic seismic activity in order to improve geophysical understanding of volcanic systems and thereby improve volcanic risk assessment.