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|Title:||Studies of atmospheric photochemistry in the European troposhere|
|Authors:||Phillips, Gavin James|
|Presented at:||University of Leicester|
|Abstract:||This thesis focuses on the photochemistry occuring in the troposphere over Europe. The use of the MRP C-130 Hercules aircraft fitted with instrumentation for the measurement of pertinent chemical and physical parameters in the study of the chemistry of the troposphere is described. The calibration and characterisation of the University of Leicester fixed band-width radiometer for the measurement of the photolysis rate coefficient of ozone is also described. This instrument was fitted to the research aircraft in order to provide a measurement of the production rate of reactive radical species in conjuction with the in-situ chemical measurements. Results from the Atmospheric Chemistry and the Transport of Ozone (ACTO) experiment are presented. The average chemical environment is shown along with the relationship between tracer correlations and air mass origins, and shows that the the region of the upper troposphere sampled during the ACTO experiment was perturbed by the lower stratosphere. The results show that influence of the stratosphere was detected as low as 5.5 km and resulted in perturbed ozone, carbon monoxide and NOy levels relative to the background troposphere. The European Export of Precursors and Ozone by Long-range Transport (EXPORT) experiment is described in detail. A study of the average altitude profiles of measured tracers shows the influence of the European continental boundary layer on the lower and middle troposphere. The origin of air masses sampled in EXPORT acertained using a back-trajectory analysis is presented. This analysis shows that the composition of the troposphere during EXPORT with respect to air mass composition and origin was highly varied. The chemical processing in these air masses was studied by the use of a chemical box model and the results are presented. The processing of HOx radicals and ozone is found to be tied to a large extent to the levels of nitrogen oxides present in the air mass. This in turn depends on the altitude and origin of the sampled air mass. A comparison of the production and loss of HOx radicals and ozone in the ACTO and EXPORT experiments is presented. The gross HOx radical production and loss rates are found to be larger in the EXPORT experiment than in the ACTO experiment. However the net production of HOx radicals is found to be similar in both experiments. Net production of HOx radicals is observed at all altitudes in both experiments, with the exception of the polluted European boundary layer sampled in the EXPORT experiment. The net ozone production in both experiments shows a similar trend with altitude: a "c" shape is observed with a net destruction observed in the lower to mid troposphere, and production at higher and lower altitudes. The effect of the polluted European boundary layer is observed in the EXPORT experiment as HOx radical levels are suppressed resulting in net loss of ozone. The influence of the stratosphere is observed in the highest altitudes sampled in the ACTO experiment. Large net destruction rates are observed as a direct result of the large ozone mixing fraction sampled in the stratospherically influenced air masses.|
|Rights:||Copyright © the author. All rights reserved.|
|Appears in Collections:||Theses, Dept. of Chemistry|
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