Ian McKendry

Widespread and persistent summer multi-day episodes characterized by dense layers of wild-fire smoke emanating from western wildfires have increased in frequency in recent years acrosswestern Canada. These events often occur under otherwise clear sky anti-cyclonic weatherconditions and have significant impacts on surface temperatures, surface radiation and energybudgets. Here, we present previously undocumented mountain-top, wildfire influencedparticulate matter concentrations and compare them to those recorded in the valley. Thedistribution of particulate matter both temporally and spatially is presented as well. The focusof this observational study is in the vicinity of Grouse Mountain, near Vancouver, BritishColumbia. Observations are made using a GRIMM 1.108 Dustcheck mini-mass-spectrometer,a Dylos DC1100 Pro air quality monitor, a mini micropulse LiDAR (light detection andranging) and vertical sounding using mini sondes (WINDSOND). The Hybrid Single ParticleLangrangian Integrated Trajectory (HYSPLIT) air pollution modelling software is usedto track parcels of wildfire smoke. Results show enhanced mountain-top particulate matterconcentrations with many instances displaying higher concentrations on Grouse than in thevalley, most commonly under anti cyclonic conditions. Evidence of a mountain boundarylayer in the presence of smoke is presented, as well as signs of suppressed convective ventingand more stable vertical profiles, likely due to the radiative effects of smoke.

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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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The accuracy of gridded precipitation products in mountainous environments has been shown to be unreliable compared to other geographic areas due to the complex terrain and sparse network of stations typically found in these regions. This study is an analysis of the accuracy of the North American Regional Reanalysis (NARR) precipitation dataset for the province of British Columbia. Unlike similar gridded precipitation products, the NARR has not yet been evaluated to determine how reliably it reproduces observed patterns of precipitation in this region. The objective of this study is to assess the temporal and spatial patterns of precipitation in the NARR record in order to determine how closely it reproduces observed precipitation. A comparison of the NARR precipitation records with station precipitation records was conducted to evaluate the NARR’s ability to reproduce the interannual, monthly, and daily patterns of precipitation experienced. Streamflow records and NARR precipitation records for a number of basins throughout British Columbia were examined using a water balance approach to better understand the spatial variability of errors. A structural break in the NARR data was observed in 2003, which led to larger inaccuracies in the NARR record in subsequent years. This break was caused by a decision to exclude Canadian rain gauge data from the NARR’s data assimilation process from 2003 onwards. Several clear spatial patterns were observed in the NARR precipitation data. The NARR underpredicted precipitation in mountainous regions due to inaccuracies in its digital elevation model (DEM). The NARR overpredicted precipitation in the northern region of BC’s Interior Plateau due to a lack of available rain gauge data in this area. Finally, the NARR was found to be more accurate at modelling precipitation in areas with flat terrain and adequate station coverage, such as the southern region of the Interior and the Northeast Plateau. This analysis has shown the spatial and temporal variability of errors in the NARR dataset, allowing users to recognize both the strengths and potential shortcomings of this tool.

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The transport of coal by train through residential neighbourhoods in Metro Vancouver, British Columbia, Canada is a growing concern for many residents living near the railway. This study aimed to identify and quantify any potential particulate matter (PM) increase caused by the presence of rail traffic adjacent to John Oliver Park in Delta, BC. Field work was carried out during August and September 2014, using a GRIMM optical particle counter that measured PM concentration at various size ranges. A select number of passing trains were confirmed visually, while the majority of passages were identified with audio data recorded by a microphone. A horizontally operating mini-micropulse lidar system was also set up at the park on three individual days to make intensive backscatter measurements. Wind data were recorded by collocated instruments maintained by Metro Vancouver. Finally, the Corporation of Delta had a dustfall measurement campaign during the same time period. Trains carrying coal are associated with a 5.28, 4.11, and 2.55 µg/m³ average increase in concentration over a 15 minute period, compared to control conditions for PM₃, PM₁₀, and PM₂₀, respectively. These increases are all statistically significant at α=0.01. PM concentrations during train passages of all types were not found to be significantly different from PM concentrations during control conditions. The presence of coal dust particles at the site was confirmed by the dustfall measurements carried out by the Corporation of Delta. Lidar backscatter imagery provided individual snapshots of train passages. However, it is clear that not every train passage causes an increase in PM concentration, and the effect appears to be highly dependent on wind direction and local meteorology.

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In recent years, the frequency of forest fires has been increasing in western North America. With an increase in forest fire activity, attention has been drawn to the negative effects forest fire smoke has on air quality and visibility. This study quantifies the relationship between smoke, air quality and visibility. Determining how much smoke produced by forest fires influences air quality and visibility will improve air quality forecasting. This study was conducted from 2007 through 2011 during the fire season (April - October) in southwestern British Columbia, focusing on the Georgia Basin airshed. A host of tools were used to determine how air quality and visibility were influenced by forest fire smoke. Satellite Fire Detection from National Oceanic and Atmospheric Administration (NOAA)’s, National Geophysical Data Centre(NDGC) was used to determine on which days during the four year period smoke was present in southwestern British Columbia. To determine where smoke particles were transported from, NOAA’s HYbrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model was used. Backward trajectories were computed from Vancouver International Airport on days which smoke was present. PM₂.₅ (particles with a diameter less than 2.5 microns) and O₃ (ozone) concentrations were examined at twelve locations. Gases and aerosols produced by forest fires are known to degrade visibility. A semi-automated approach was used to calculate visibility using digital images. Southwestern British Columbia's air quality and visibility was negatively influenced by smoke. Up to 30% of summer days in the Georgia Basin airshed were influenced by smoke. The summer of 2009 experienced the most smoke days. Smoke and aerosol concentrations were largely influenced by dominating weather patterns. Two weather patterns dominate in the Georgia Basin airshed on smoke days. One pattern creates favourable conditions to produce forest fires and the other is likely to transport smoke from the interior of British Columbia into the Georgia Basin airshed. Concentrations of fine particulate matter increased on average by 5 µgm⁻³ and ozone increased by 7 ppb when smoke was present. Visual range (VR) decreased on average by 60 km and estimated extinction values increased during smoke events.

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Temperature structure within complex terrain is fundamental to determining stability, thermally-induced circulations, and mountain weather, all of which impact those living, working, and recreating within it, as well as those external to it that depend on water from snowmelt. While numerous studies and text books outline many factors affecting slope air and free air temperatures, the interactions of these factors with the complex terrain makes predictability of temperature structures very difficult. This is further compounded by sparse observational data that has limited representativeness due to numerous localized effects. In preparation for the 2010 Olympic and Paralympic Winter Games, temperature sensors were placed along the west slope of Whistler Mountain, and radiosondes were launched twice daily, creating a rare opportunity to investigate slope and free air temperature structure and evolution within a mountain valley. Daytime and nighttime temperature profiles are categorized by cloud cover, and very consistent lapse rates are found within categories. Profiles are compared for slope and free air within each category, and between categories. Case studies provide further detail in describing temperature structure evolution. Clear days give rise to the least uniform slope air temperature structure, but a consistent, fairly representative, linear lapse rate is nonetheless found. Overcast conditions effectively eliminate microclimates, producing a relatively linear slope air temperature structure. Additionally, consistent free air lapse rates are defined for each cloud cover category. While the majority of slope and free air lapse rates are statistically indistinguishable, significant slope-free air temperature differences still exist. Lastly, linear regression is used to develop an equation that successfully determines slope air temperatures from a given free air temperature, or vice versa. Together with the representative lapse rates, one is able to construct slope and free air temperature profiles given a single slope or free air temperature measurement. These results show that by separating profiles by weather condition, consistent temperature structures and relations can be extracted from a seemingly incoherent collection of complex mountain slope and free air profiles. In doing this, it becomes feasible to accurately predict these profiles, providing great utility to those impacted by mountain temperatures.

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An observational study was conducted to characterize atmospheric conditions at an air chemistry monitoring site on the summit of Whistler Mountain, British Columbia, Canada. Discrimination of air samples from the observatory as either representative of the free troposphere (FT) or modified by air from the valley-based planetary boundary layer (PBL) is critical to the proper interpretation of air chemistry datasets. Atmospheric data from a one-year study period were used to evaluate indicators and possible driving forces of PBL influence at the Whistler site. Diurnal cycles in water vapour and aerosol concentration were attributed primarily to convective uplift of PBL air during daytime heating hours. Analysis of these variables found that PBL influence was common in the spring and summer months and relatively rare in late fall through early winter. For the one-year period, 37% of the days had diurnal cycles in aerosol concentration that were considered typical of thermally induced vertical transport processes. Patterns of slope and valley winds were also identified for Whistler, and the presence of these diurnal wind systems was associated with enhanced aerosol concentration at the summit. Synoptic classification methods were used to describe the prevailing conditions on days with well-defined indicators of PBL influence. Strong solar insolation and light synoptic scale winds were found to be common on such days. Case studies of particular days confirmed that a deep convective boundary layer (CBL) of well-mixed air can encompass the mountain summits, even during the winter season. During the summer, a tendency for PBL constituents to remain aloft through the night means that the summit observatory can be unrepresentative of the FT for several days at a time. Separation of air chemistry measurements into periods of FT conditions and times of PBL influence requires careful analysis of a variety of datasets on both local and regional scales.

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