Sources of Wintertime Atmospheric Organic Pollutants in a Large Canadian City: Insights from Particle and Gas Phase Measurements

Although atmospheric organic pollutants have been extensively studied to elucidate summertime urban photochemical air pollution, uncertainties remain concerning the quality of wintertime air in large northern North American cities. Here, we used online mass spectrometric measurements of volatile organic compounds (VOCs) and organic aerosol (OA), combined with positive matrix factorization (PMF), to identify sources of organic pollutants in downtown Toronto, Canada during February–March 2023. In some cases, comparable PMF factors were identified for both VOCs and OA, such as from traffic, cooking, and background oxygenated sources. However, VOC PMF yielded additional information, such as a factor associated with human-related emissions of VOCs. Additionally, VOC PMF yields two traffic factors: one likely related to gasoline and one to diesel use. Despite cold and relatively dark conditions, the OA and VOC oxygenated factors both grow in intensity during the daytime, indicative of photochemical activity, whereas the traffic and cooking factors were enhanced in the morning and late evening due to the timing of vehicle use, cooking, and boundary layer effects. This study illustrates the benefits that arise from the parallel source–receptor analyses of organic gases and aerosol particles.