The Lower Fraser Valley, straddling the USA-Canada border in western North America, often experiences episodes of elevated tropospheric ozone in summertime. The meteorology governing those episode days is characterized by a stagnant high pressure system, light wind, strong insolation and the occurrence of sea breezes. To shed some light on the mesometeorology of ozone episodes in the LFV, this study employed the Regional Atmospheric Modelling System from Colorado State University, a non hydrostatic, three-dimensional mesoscale modelling system to simulate the detailed structure of air flows over the valley for one specific episode day. Significant code modifications have been made to enhance the model's ability to represent surface energy fluxes and predict surface temperatures in the surface of complex terrain and land-use patterns. Evaluation of the model performance was made against an extensive set of observation son the episode day. Pollutant transport on the modelling day was explored with a Lagrangian particle dispersion model. Specifically, forward trajectories were calculated for particles released at various locations in the Lower Fraser Valley and at different times. A systematic qualitative and quantitative model evaluation with the statistical method of Willmott showed that the model could adequately simulate the observed sea breeze another interactive terrain-induced flows such as slope wind and channel flow. Trajectory studies indicated that pollutant recirculations occurred largely from sources originating in the northwest part of the valley where most emission sources are located, and ended in a region where the highest ozone concentrations were observed. Recirculations were due to pollutants traveling with the interactive flows of sea breeze and upslope winds, and later being captured and directed back to the valley by the down slope winds. Particles released in other part of the valley all travelled outside the valley, having a minimal contribution to the episode buildup.

The Lower Fraser Valley, straddling the USA-Canada border in western North America, often experiences episodes of elevated tropospheric ozone in summertime. The meteorology governing those episode days is characterized by a stagnant high pressure system, light wind, strong insolation and the occurrence of sea breezes. To shed some light on the mesometeorology of ozone episodes in the LFV, this study employed the Regional Atmospheric Modelling System from Colorado State University, a non hydrostatic, three-dimensional mesoscale modelling system to simulate the detailed structure of air flows over the valley for one specific episode day. Significant code modifications have been made to enhance the model's ability to represent surface energy fluxes and predict surface temperatures in the surface of complex terrain and land-use patterns. Evaluation of the model performance was made against an extensive set of observation son the episode day. Pollutant transport on the modelling day was explored with a Lagrangian particle dispersion model. Specifically, forward trajectories were calculated for particles released at various locations in the Lower Fraser Valley and at different times. A systematic qualitative and quantitative model evaluation with the statistical method of Willmott showed that the model could adequately simulate the observed sea breeze another interactive terrain-induced flows such as slope wind and channel flow. Trajectory studies indicated that pollutant recirculations occurred largely from sources originating in the northwest part of the valley where most emission sources are located, and ended in a region where the highest ozone concentrations were observed. Recirculations were due to pollutants traveling with the interactive flows of sea breeze and upslope winds, and later being captured and directed back to the valley by the down slope winds. Particles released in other part of the valley all travelled outside the valley, having a minimal contribution to the episode buildup. / Arts, Faculty of / Geography, Department of / Graduate

Surface deposition is an important sink for tropospheric ozone. The rate of ozone deposition may be measured by measuring the downward flux of ozone in the atmospheric surface-layer. This thesis presents eddy correlation measurements of ozone fluxes, taken on eight days in August, 1994, at a grassland site located in the Lower Fraser Valley of British Columbia. Surface resistances to ozone deposition were calculated from the flux measurements. Much of the variability in measured surface resistances was found to be attributable to variations in ambient light levels and in the degree of moisture stress at the site. Measurements of surface resistance from this site agreed quite well with other measurements of ozone deposition to grassland surfaces. Measured surface resistances were compared to surface resistances calculated using the Wesely (1989) parameterization (W89) for surface resistance. W89 underestimated surface resistance, particularly in the mid afternoon and early evening. This was attributed to the model's neglect of the effects of water stress on stomatal resistance, as well as to a low value for resistance to ground surface deposition in the model. The eddy correlation fluxes were compared to ozone fluxes derived using an assumption of cospectral similarity between ozone and heat flux and to ozone fluxes measured using the variance method and the gradient method. The cospectral similarity method worked well and allowed a considerable relaxation of the sampling speed requirements of the eddy correlation method. The variance method produced biased flux measurements due to high frequency noise from the ozone sensor. Flux measurements using the gradient method had a great deal of scatter, due to inaccuracies in the measurement of gradients.

Surface deposition is an important sink for tropospheric ozone. The rate of ozone deposition may be measured by measuring the downward flux of ozone in the atmospheric surface-layer. This thesis presents eddy correlation measurements of ozone fluxes, taken on eight days in August, 1994, at a grassland site located in the Lower Fraser Valley of British Columbia. Surface resistances to ozone deposition were calculated from the flux measurements. Much of the variability in measured surface resistances was found to be attributable to variations in ambient light levels and in the degree of moisture stress at the site. Measurements of surface resistance from this site agreed quite well with other measurements of ozone deposition to grassland surfaces. Measured surface resistances were compared to surface resistances calculated using the Wesely (1989) parameterization (W89) for surface resistance. W89 underestimated surface resistance, particularly in the mid afternoon and early evening. This was attributed to the model's neglect of the effects of water stress on stomatal resistance, as well as to a low value for resistance to ground surface deposition in the model. The eddy correlation fluxes were compared to ozone fluxes derived using an assumption of cospectral similarity between ozone and heat flux and to ozone fluxes measured using the variance method and the gradient method. The cospectral similarity method worked well and allowed a considerable relaxation of the sampling speed requirements of the eddy correlation method. The variance method produced biased flux measurements due to high frequency noise from the ozone sensor. Flux measurements using the gradient method had a great deal of scatter, due to inaccuracies in the measurement of gradients. / Arts, Faculty of / Geography, Department of / Graduate