BBOA Collection. Forest fire BBOA was collected on 47 mm PTFE membrane filters (MTL, USA) at the University of British Columbia -Okanagan (Kelowna, Canada) and Thompson Rivers University (Kamloops, Canada) (see sample locations in Figure ) in early August 2021 during heavy forest fire activity. Here we focus on two samples: one collected in Kelowna from August 3 rd to August 6 th and one collected in Kamloops from August 2 nd to August 5 th . PM2.5 concentrations during the two sampling periods reached over 200 µg m -3 , according to British Columbia air quality monitoring stations located in the same cities as the collection sites (Figure ). The air quality monitoring stations were approximately 10 km away in Kamloops and 2 km away in Kelowna. Data was acquired from the BC Air Data Archive Website. 67 PM2.5 concentrations during sampling were on average higher in Kamloops than in Kelowna (Figure , Table ). From January 1 st 2021 to June 20 th 2021, before the start of the wildfire season, the mean daily PM2.5 concentrations in Kelowna and Kamloops were 4.8 and 5.5 µg m -3 , respectively (Figure , Table ).