A model analysis of anthropogenic influences on ozone and related species: The interaction of transport and chemistry

In the first part of this thesis, the UIUC's two-dimensional chemical transport model (2D CTM) is employed to investigate possible effects of heterogeneous reactions of ozone on aircraft-generated carbon particles. Several studies in modeling atmospheric processes have suggested that heterogeneous chemistry on soot emitted from high altitude aircraft could affect stratospheric ozone depletion. However, these modeling studies were limited because they did not adequately consider the decrease in reaction probability with time as the surface of the soot becomes "poisoned" by its interactions with various gases. The UIUC's 2D CTM is therefore implemented to calculate ozone uptake probabilities and determine the available active sites on soot given partial pressures of the reactants, temperature, and time since soot emission in order to investigate ozone decrease. The results show that, even if active sites on soot surfaces are regenerated, upper tropospheric and lower stratospheric ozone losses on aircraft emitted soot occurring through heterogeneous reactions are insignificant once poisoning effects are considered.;Significant seasonal variations in the concentrations of several trace gases were observed in the southern tropical Pacific during the PEM-TROPICS-A (PT-A) and PEM-TROPICS-B (PT-B) campaigns. In the second part of this thesis, a 3D CTM, MOZART, is used to investigate the ozone budget and identify its controlling factors over this region. The model reproduced the main features of the observed seasonal variation in ozone and CO. The ozone burden during the PT-A was larger due to the transport of ozone into the central Pacific middle-troposphere from the west, whereas a net outflow of ozone from this region to the east resulted in a reduction of ozone burden during the PT-B period. Transport of ozone from the Northern Hemisphere into this region was found to be much larger during the PT-B period compared to the PT-A period. Results from MOZART were also used to generate correlations in the ratios of non-methane hydrocarbons and the variability in their mixing ratio distributions as a function of their local lifetimes. Comparisons between this correlation with experimental observations enabled us to identify a source-receptor relationship over the southern tropical Pacific region.