UBC Theses and Dissertations

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UBC Theses and Dissertations

The morphology of, and impact of wildfire smoke on the development of, the convective boundary layer over Southwestern British Columbia Ferrara, Madison R.


The Weather Research and Forecasting (WRF) model was used to understand spatial and temporal variations in convective boundary layer (CBL) height over Southwestern British Columbia. The model was evaluated with several vertical profiles collected by Windsond weather balloons and was found to be in good agreement with observed data. A comparison between terrain height and CBL height showed that the CBL is more terrain following in the morning and less terrain following in the afternoon. This behaviour was further quantified by calculating r and T values for each hour using mean CBL height data for each month. The least terrain following behaviour occurred at 1400 PST for each month. Mean CBL depth (above ground level) was contoured over the study region and showed that the CBL tended to grow deepest in the eastern half of the Fraser Valley, however, several mountain peaks had a CBL depth similar to those observed over the valley. Mean CBL height (mean sea level) showed that, for all mountain peaks, the CBL was higher than all locations over the Fraser Valley. The large spatial variations in CBL height were shown to be able to result in the formation of elevated layers over the valley via advective venting. A thick layer of wildfire smoke that was present in the lower atmosphere during summer 2017 was documented to understand the impact it had on CBL development. The plume had an aerosol optical depth (AOD) of about 4 during the most intense period and PM₂.₅ concentrations exceeded 50 µg/m³. Windsond profiles collected before and during this event showed a more stable atmosphere existing on the smoke day. The potential temperature gradient was higher near the surface and lower aloft when smoke was present in the atmosphere compared to the clear day. It has been speculated that the impact on atmospheric stability due to wildfire smoke can act as a feedback loop by suppressing CBL growth, allowing pollutants to accumulate in the lower atmosphere, thus further degrading air quality.

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