10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Apportionment of Black Carbon to Fossil Fuel and Biomass Burning Sources in the Lower Fraser Valley, British Columbia: Impact of 2017 Wildfires on Local Air Quality
Robert Healy, Geoff Doerksen, UWAYEMI SOFOWOTE, Yushan Su, Jerzy Debosz, Michael Noble, Cheol H. Jeong, Jon M. Wang, Nathan Hilker, Greg J. Evans, Anthony Munoz, Ontario Ministry of the Environment and Climate Change
Abstract Number: 584 Working Group: Carbonaceous Aerosol
Abstract One year Aethalometer datasets collected concurrently at six sites in the Lower Fraser Valley, British Columbia from September 2016 through August 2017 have been analyzed in order to investigate the relative importance of fossil fuel and biomass burning contributions to black carbon (BC) in the region. The sampling sites are located in North Vancouver, Richmond, South Burnaby, Port Moody, Abbotsford and Chilliwack. These sites experienced annual mean BC mass loadings in the range 0.3-0.7 µg m-3, with the highest concentrations observed in Vancouver and the lowest in Chilliwack, a small city located approximately 100 km east of Vancouver. BC was apportioned to fossil fuel and biomass burning sources at hourly resolution using the dual-wavelength optical model approach, first incorporating assumed alpha values of 0.90 and 2.09, respectively. However, applying a value of 2.09 was found to significantly underestimate the fraction of BC from biomass combustion (BCbb) during a prolonged wildfire smoke event which persisted for 10 days in August 2017 and impacted air quality severely in the region. Hourly resolution PM2.5 concentrations in excess of 100 µg m-3 were recorded several times at multiple sites during this event and mean ambient PM2.5 concentrations for the 10 day period were up to eight times higher than mean concentrations for the remainder of the summer. Using a difference approach to estimate the BC mass associated with the wildfire plume enabled an optimization of the alpha value for wildfire aerosol at each site. Similar wildfire alpha values were determined at all six sites using this approach 1.40 ± 0.10, which is sensible considering that all sites were influenced simultaneously by the same plume. The highest hourly resolution wildfire BCbb mass loadings were observed at Chilliwack (7.3 µg m-3), which is situated closest to the wildfire source regions, identified using conditional probability function and quantitative transport bias analyses. For the Lower Fraser Valley sites investigated, approximately 34-45% of total summertime exposure to BC and 64-86% of total summertime exposure to BCbb occurred during the 10 day wildfire event. On an annual scale, however, residential wood combustion is estimated to be a larger contributor to ambient BC than wildfires at every site.