Air quality is an international issue which has been the subject of several European directives on pollution levels as atmospheric pollutants can have significant effects on human health, ecosystems and climate change, especially at high levels. In the UK the largest sources of atmospheric pollutants are products of combustion from power generation and motor vehicles including NO[subscript x] (NO and NO[subscript 2]), CO, VOCs and particulate matter. Hence it is becoming increasingly important to measure changes in these air pollutants especially in urban areas where these pollutants are at the highest levels. Differential Optical Absorption Spectroscopy is now commonly used as an air quality tool; primarily through the measurements of nitrogen dioxide (NO[subscript 2]). CityScan is a Hemispherical Scanning Imaging Differential Optical Absorption Spectrometer (HSI-DOAS) which has been optimised to measure concentrations of NO[subscript 2]. This thesis will describe the development and subsequent deployment of three CityScan instruments and the first results from these deployments. CityScan has a 95° field of view (FOV) between the zenith and 5° below the horizon. Across this FOV there are 128 resolved elements which are measured concurrently, the spectrometer is rotated azimuthally 1° per second providing full hemispherical coverage every 6 minutes. Three CityScan instruments were built between 2009 and 2012 and deployed in various locations, including Leicester, London and Bologna. Data from one of these instruments has been validated with a MAX-DOAS instrument (TROPOGAS) and in situ monitors. The comparison with the TROPOGAS instrument produced gradient values between 0.7 and 1 with R² values rarely lower than 0.7. An NO[subscript 2] detection limit of CityScan has been calculated to be 4 x 10[superscript 15] mol cm[superscript -2]. The extensive field of view of the CityScan instruments has allowed NO[subscript 2] concentrations to be mapped on city-wide scales allowing areas of high and low pollution to be identified with a spatial resolution which has never been possible before without the use of models.

Numerous current environmental problems result from changes to the trace gas composition of the Earth's atmosphere. Issues such as smog formation, acid rain and stratospheric ozone depletion all result from the chemical transformation of pollutants in the atmosphere and understanding the nature and rapidity of these chemical changes is consequently an important goal of atmospheric science. Laboratory studies of the kinetics and product channels of important atmospheric reactive species - atoms and free radicals - aim to provide data for inclusion into numerical models to simulate changing atmospheric compositioa Typically, the limitation of such laboratory studies is the sensitivity required for monitoring very low concentrations of very short-lived gas phase species. The work described in this thesis addresses mislimitation in new instrument development and in application of an existing instrument to studies of reactions of the atmospherically important CIO free radical. This thesis therefore describes two principal areas of research. In the first part, the design, construction, and testing of an experimental technique for the study of gas phase chemical reactions in a flow system are detailed. This apparatus consists of a conventional discharge flow tube in which reactions take place, coupled to a novel detection system This detection, based upon chemical ionisation mass spectrometry (CIMS), uses a novel chemical ionisation scheme using proton transfer from H3+ ions. A high-pressure electrical discharge system using H2 has been developed and used as the source of H3+ An electrostatic ion guide has also been designed and tested to transport ions efficiently from their region of interaction with the gas under study, to the detector. Experiments to characterise the detection efficiency and instrumental sensitivity have been carried out, along with studies of a variety of chemical systems.

A mesoporous silicate has been developed for the removal of volatile organic compounds (VOCs). The indoor air pollutants of interest were formaldehyde, toluene, ethylbenzene, o-xylene, cumene and dichlorobenzene. The indoor air pollutants were actively sampled onto (i) Tenax filled sampling tubes and subsequently analysed by thermal desorption gas chromatography mass spectrometry or (ii) chemically modified C₁₈ silica cartridges analysed by high performance liquid chromatography ultraviolet spectroscopy. A pollutant atmosphere suitable for testing the sorbents chambers were created in-house. Mesoporous silicates were synthesised to control the surface area, pore size and pore volume of the material. Several preparation methods were used to produce the final mesoporous silicate sorbent. The mesoporous silicates were mainly synthesised using tetraethyl orthosilicate as a precursor with either a quaternary ammonia silicate or triblock copolymer as the organic template synthesising MCM-41 and SBA-I5, respectively. A selection of the successfully synthesised mesoporous silicates were modified with propyl amine to investigate the possibility of formaldehyde chemisorption. Material characterisation was performed using powder x-ray diffraction, transmission electron microscopy, scanning electron microscopy, nitrogen adsorption and elemental analysis. Sorbents were selected for adsorption efficiency testing based on the characterisation results. The synthesised mesoporous sorbent VOC and formaldehyde adsorption efficiencies were then compared with commercially available sorbents. It was observed that the commercial sorbents were inefficient at adsorbing both the formaldehyde and the selected VOCs. The modified sorbents adsorbed formaldehyde strongly compared to the unmodified parent sorbent. However when using the modified mesoporous silicate an unwanted release of toluene was also recorded. Simulated closed environments were generated with the selected VOCs. SBA-15 was efficient in reducing the VOC chamber concentration over a period of 2 hours. SBA -15 adsorbed ethylbenzene, cumene and dichlorobenzene with efficiency rates of 89.4, 99.9 and 97.7 %, respectively. The adsorption efficiency for toluene was reduced at 35.4 %.

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