Potential multi-path spectroscopic differential absorption systems for the measurement of trace gases in the atmosphere are presented. Recommendations are made for system designs to be used for tomographic differential optical absorption spectroscopy (DOAS) measurements. The difficulties in producing multiple simultaneous beams from a single artificial light source are discussed, while the need for further tomographic resolution information is highlighted. An innovative prototype scanning-DOAS system is presented. The system is designed to generate multiple sequential paths, without the need for bulky and expensive mechanical systems. The scanning DOAS system can easily be placed in an industrial production plant or in a street canyon for multiple direction monitoring. The scanning DOAS system is currently being tested at the Cork Institute of Technology (CIT).
We present the results of preliminary research investigating the generation of two-dimensional pollutant gas concentration maps of street canyons. This research uses computed tomography (CT) to reconstruct the spatial distribution of gas concentrations from path-integral data obtained using differential optical absorption spectroscopy (DOAS). This work represents a novel application
of these two techniques and is aimed at the validation of theoretical gas distribution models in selected urban settings. The derived results are based on model data and investigate the
viability of constrained geometry sensing networks and the accuracy of current computed tomography algorithms. We also present results on the use of an evolutionary algorithm applied to pollutant reconstruction in an open area as part of initial investigations
into its applicability to street canyon pollutant reconstruction. Future work will include the reconstruction of gas distributions in a real urban setting with the long-term goal of a system that is capable of performing this task in near real-time allowing the visualisation of short to medium time scale spatial dynamics.