Long path Fourier transform absorption spectroscopy for investigating pollution in the urban boundary layer
The control of atmospheric pollution in the urban environment has, in recent years, taken on important local, national and international significance. Legislation has been introduced in many countries to improve air quality in urban areas. Monitoring air pollution is an important part of understanding and improving air quality. Current standard methods of measuring air pollution only monitor at a single point in space which can lead to ambiguities when assessing air quality over an extended region, such as a city centre or a road intersection. Optical remote sensing techniques, such as long path Fourier transform absorption spectroscopy, overcome the limitations of point measurements by integrating over long paths and thus measuring the average ambient pollutant concentrations. A commercially available Fourier transform infrared (FTIR) spectrometer, together with custom built external optics has been used to make measurements of air pollution in Oxford city centre. It has been shown that it is possible to measure the concentrations of several pollutants simultaneously and in short measurement times. Issues relating to the performance of the spectrometer have been studied, their effects quantified and solutions proposed. Optimal estimation techniques have been applied to the analysis of the single beam spectra recorded by the FTIR spectrometer. This technique has previously only been applied to radiance and transmission spectra and so extensions were necessary. High resolution laboratory measurements of the absorption cross-sections of benzene and 1,3-butadiene have been made and the potential for detecting them in ambient urban air determined.