Development and Application of Methods based on DOAS and FTIR Absorption Spectroscopy for Atmospheric Research
Doctoral thesis, 1999
Over the past decades concern about the environmental impact on our atmosphere from human activities has been constantly increasing. From the recognition of local industrial pollution in the first part of this century, over regional scale problems related to urbanisation and growth of traffic systems to global environmental problems such as climate change and stratospheric ozone depletion. Today these questions are high on the political agenda, manifested by political agreements like the Montreal protocol with amendments aiming at a total ban of the CFCs responsible for stratospheric ozone depletion, and the Kyoto protocol regulating the emissions of gases affecting the global climate. In parallel with this increased awareness of environmental problems, there has been a strong development in instrumentation and measurement strategies to study basic atmospheric processes, quantify emissions and monitor the state of the atmosphere. In this context, optical remote sensing techniques such as DOAS and Long Path FTIR have played, and are still playing, an important role.
This dissertation deals with the development and application of instrumentation and measurement strategies based on long path UV and IR absorption spectroscopy for atmospheric research. The instrument development comprises a novel design of a transmitting/receiving telescope facilitating the use of single ended DOAS measurements and a unique 1 km open multireflection cell which, combined with an FTIR spectrometer, is capable of ppb level measurements of a large number of different gases. A shorter version of the system, with 200 m optical path, has proven very valuable for industrial hygiene studies. The measurement strategy development involves the use of dual beam DOAS spectroscopy to improve background concentration monitoring, an approach to studying emissions from aircraft using zenith sky DOAS, the development of the Time Correlation Tracer technique for measurements of fugitive emissions, various gradient methods and the megachamber concept for area integrated measurements of biogenic emissions.
The various instruments and techniques have been applied in a large number of field campaigns including measurements of: SO2, NO2, NO, O3, HNO2, and CH2O in urban and background air; biogenic emissions of N2O, CH4, and CO2 from various ecosystems; NH3, N2O and NO from liquid manure spreading; ethylene, propylene, ammonia and various hydrocarbons from industrial activities; terpenes, peracetic acid, ammonia and various hydrocarbons from indoor industry; total methane emission from landfills; and total columns of O3, NO2, HC1, HNO3, HF, ClO, COF2, N2O and ClONO2 of importance for stratospheric ozone depletion. All this work has been carried out in strong international collaboration.
Despite the sometimes demanding environmental conditions, the optical methods have proven to be reliable and competitive tools for increased understanding of our atmospheric environment, thus providing a solid ground for political decisions aiming at minimizing the negative impact of human activities on our planet.