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Ozone (03) and nitrogen dioxide (N02) are two of a series of air pollutants targeted in the UK Air Quality Strategy, by virtue of their adverse effects on human health and the natural environment. Because 03 and N02 are rapidly chemically inter-converted in the atmosphere, their behaviour is coupled and they can be collectively referred to as 'oxidant' (OX). Sources and trends of OX in the UK have been examined through a combination of dedicated field measurements of 03, N02 and nitric oxide (NO), over three years (January 2005 - December 2007) at the Silwood Park Atmospheric Research Station (SPARS) near Ascot; and through analysis of data for the same species at 31 sites across the UK, which are part of the UK Automatic Urban and Rural Network (AURN). SPARS measurements have contributed to data available from the London Air Quality Network (LAQN), the site being referred to as "Windsor and Maidenhead - Ascot" (MW3). Total Oxidant [OXh can be interpreted in terms of: (i) a Global hemispheric baseline, [OX]H, representing the baseline air transported into the UK; (ii) a Regional modification, [OX]R, which has contributions from production via regional-scale photochemical processing of emitted volatile organic compounds (VOC) and nitrogen oxides (NOx), and loss via deposition; and (iii) a Local enhancement, [OX]L, from direct emissions of N02 (e.g., road vehicle exhaust). Separation of these components involved an air mass screening methodology, using back-trajectories calculated with meteorological models. [OX]H makes the major contribution to [OXh at rural and polluted urban centre sites, although either of the other components can dominate during episodes. [OX]R is typically enhanced during the period from April to September when meteorological conditions are favourable and photochemical processes operate efficiently. [OX]L is largest at polluted urban sites close to emission sources, and maximises in the winter months when dispersion is least efficient. Abstract Annual mean data since the 1990s show an increasing trend for [OX]H (a consequence of increasing emissions of methane and NOx), while [OX]R and [OX]L show decreasing trends because of emissions control strategies within the EU and UK. Seasonal and spatial variations in [OX]H and [OX]R are valuable for forecasting and modelling 03. [OX]H is important for policy when baseline 03 concentrations exceed international air quality standards. 11.

Particulates in the atmosphere can have a significant effect on human health and climate. Combustion is a major source of atmospheric particulates and primarily originates from the burning of fossil fuels and biomass. This work concentrates on the combustion of three compounds; n-decane to represent hydrocarbon fossil fuels, eugenol to represent the lignin component of biomass and furfural to represent the holocellulose component of biomass. The use of proxy compounds eliminates contaminants found in natural biomass samples and results can later be applied to studies of more complex structures. Combustion is carried out using a diffusion type burner and analysis techniques include the use of two single particle mass spectrometers (ATOFMS and SPLAT) and an SMPS. Results are presented for the analysis of soot generated by combustion of the named fuels. Fractal dimension values of n-decane and eugenol soot decrease by approximately 10% from early to late stage combustion indicating an increase in the irregularity of particle shape but furfural soot values increase by 4% indicating a small increase in particle sphericity. Comparison of soot produced by the three fuels reveals significant differences in the molecular structure of their P AHs; n-decane soot is dominated by 4-ring P AHs and their alkyl derivatives, eugenol soot is dominated by 4-ring P AHs and ions with larger mJz values separated by 12 and 24 amu, and furfural soot is dominated by 3-ring and 4-ring PAHs and their alkyl derivatives. Results show that the specific processes to form P AHs from each fuel are not identical but there are similarities and they could be explained by a number of soot formation pathways with a different contribution from each pathway for each fuel. No evidence is found of oxygenated compounds in the soot from any fuel.

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One of the major issues in road transport today is poor air quality and the associated negative health impacts. In particular, diesel vehicles are found to contribute substantially to atmospheric levels of particulate matter (PM) and ozone (O3). Pollutant mass emission rates from motor vehicles vary greatly according to their operating mode. Consequently, changes in road layout or traffic behaviour may have a significant impact on local air quality. Improved understanding of the underlying emission mechanisms can help at the traffic planning stage in order to assess environmental impacts and aid in the design of more efficient air quality management methods. However, existing planning tools do not adequately represent the variable and transient nature of pollutant emission rates from vehicles, especially with regard to emissions of PM. This thesis addresses the issue of how motor vehicles, and in particular, light-duty diesel vehicles contribute to local air pollution. It does so with reference to a series of experiments conducted with a 1999 model-year Ford Focus turbo-diesel test vehicle. The vehicle was equipped with an on-board monitoring system developed and validated for this research to address the shortcomings of existing devices. The resultant data are used to examine the second-by-second mass emission rates of pollutant species, including PM. The extension of an existing instantaneous model for gaseous pollutants to represent PM emissions is then examined, with an adjustment to the model structure found to improve emission estimates. The experimental techniques developed in this thesis are compared to reference data obtained using a chassis dynamometer emissions test facility. The models are compared to the on-board measurements for both laboratory and on-road tests. These comparisons show that on-board monitoring offers a more precise representation of the pollutant mass emission rates than the modelling techniques considered. Nevertheless, the model performance is sufficiently good to suggest that realistic estimates may be obtained through the simulation of vehicle trajectories and the associated pollutant emission rates. Importantly, the techniques developed in this research are able to replicate the high-emission episodes associated with transient vehicle operation. This offers the possibility to assess the impact of traffic management schemes on PM emission levels more accurately than has previously been possible.