Regional Scale Modelling of Boundary Layer Ozone and Influences of Climate Change
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Ozone is a major air quality parameter, a key player in atmospheric chemistry and instrumental in greenhouse gas forcing. Consequently, the subject of ozone pollution warrants significant consideration in the construction of efficient pollution control measures. Ozone is a powerful oxidising agent, and has a complex chemistry with nonlinear relationships between precursors and ozone formation. In order to make any worthwhile predictions about the future of ozone levels their consequences for the earth's climate, models must have the ability to simulate accurately ozone trans- port, chemistry and long term trends accurately. Existing climate models have not been able to reproduce the rising trends in background ozone levels that have been observed at remote marine sites. This calls into question the ability of such models to predict future ozone trends. Background ozone levels are influenced by the hemispheric transport of ozone and relevant removal processes during such transport. One such removal process is the dry deposition of ozone to the ocean surface. Although the downward flux of ozone to land surfaces exceeds the downward flux to water by an order of magnitude, the dry deposition of ozone to water surfaces is a sizeable removal process for tropospheric ozone given that two thirds of the earth's surface is covered by water. The mechanisms involved in the deposition process are not entirely understood, current knowledge on dry deposition being unable to account for some elevated flux measurements. The enhancement of ozone deposition due to reactions between ozone and organic matter has been identified as a possible mechanism accelerating the rate of dry deposition, but the kinetics ofsea-surface reactions between ozone and organic matter are still relatively unknown,as is the effect of these reactions on deposition rates of ozone to the ocean. This thesis advances the current knowledge of processes governing the dry deposition of ozone to the ocean and investigates the effects of emission mitigation and changing meteorology on air quality with respect to tropospheric ozone levels using regional climate model, REMOTE. Results show that although modelled boundary layer ozone levels are relatively insensitive to the rate of ozone deposition, an upward flux of iodine compounds occurs as a consequence of marine ozone deposition. This flux is sensitive to the deposition rate and was quantified as being of potential global significance. Further results indicate a photoenhancement of reactions influencing ozone deposition which may bridge the gap between observed elevated flux measurements and flux magnitudes accounted for by current theory. Finally, the effect of changing precursor emissions and changing meteorology on future ozone pollution levels was investigated. Results suggest that over the European mainland, future ozone levels will be predominantly driven by emissions whereas in the clean marine environment of the North East Atlantic, changing meteorology will predominate in determining future ozone levels.
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