Contribution of Charge-Transfer Complexes to Absorptivity of Primary Brown Carbon Aerosol

Light-absorbing organic aerosol, or brown carbon (BrC), has significant but poorly constrained effects on climate. A large fraction of the absorptivity of ambient BrC is unassigned, and organic charge-transfer (CT) complexes have the potential to contribute to this fraction. Here, the contributions of CT complexes to the absorptivity of laboratory-generated BrC and ambient aerosol material influenced by biomass burning have been investigated, using a wide range of chemical, spectroscopic, and physical analyses. Chemical functionalization experiments are inconclusive about the role of CT complexes, whereas fluorescence spectra exhibit distinct spectral features indicative of individual chromophores. Determinations of the concentration and temperature dependences of absorbance are more conclusive. In particular, for laboratory-generated BrC extracted in either water or methanol, absorbance scaled linearly with orders-of-magnitude changes in concentration, indicating that intermolecular complexes do not contribute to the absorptivity. Furthermore, whereas the absorbance of BrC extracts in dimethyl sulfoxide exhibited a slight temperature dependence, consistent with a 15% contribution from intramolecular CT complexes at 15 °C, the complete temperature independence of absorbance of water-soluble extracts from surrogate and ambient BrC indicates a negligible role for CT complexes. Overall, our results find little evidence for CT complexes in the primary BrC studied, suggesting that they do not contribute significantly to the missing absorptivity of ambient BrC

Exploring Conditions for Ultrafine Particle Formation from Oxidation of Cigarette Smoke in Indoor Environments

Cigarette smoke is an important source of particles and gases in the indoor environment. In this work, aging of side-stream cigarette smoke was studied in an environmental chamber via exposure to ozone (O₃), hydroxyl radicals (OH) and indoor fluorescent lights. Aerosol mass concentrations increased by 13–18% upon exposure to 15 ppb O₃ and by 8–42% upon exposure to 0.45 ppt OH. Ultrafine particle (UFP) formation was observed during all ozone experiments, regardless of the primary smoke aerosol concentration (185–1950 μg m^–3). During OH oxidation, however, UFP formed only when the primary particle concentration was relatively low (<130 μg m^–3) and the OH concentration was high (∼1.1 × 10⁷ molecules cm^–3). Online aerosol composition measurements show that oxygen- and nitrogen- containing species were formed during oxidation. Gas phase oxidation of NO to NO₂ occurred during fluorescent light exposure, but neither primary particle growth nor UFP formation were observed. Overall, exposure of cigarette smoke to ozone will likely lead to UFP formation in indoor environments. On the other hand, UPF formation via OH oxidation will only occur when OH concentrations are high (∼10⁷ molecules cm^–3), and is therefore less likely to have an impact on indoor aerosol associated with cigarette smoke

The Green Chemistry Initiative’s contributions to education at the University of Toronto and beyond

The Green Chemistry Initiative (GCI) is a student-led group founded in 2012 with the primary mission of promoting green chemistry education at the University of Toronto. In order to achieve this, the GCI’s activities have included undergraduate curriculum development, arrangement of an external speaker seminar series, and organization of an annual three-day symposium along with biweekly trivia challenges. To broaden education beyond the Department of Chemistry, a successful YouTube video campaign articulating the Twelve Principles of Green Chemistry in an accessible manner has also been undertaken (acquiring over 40,000 views), in addition to monthly blog posts and conference/outreach presentations. Descriptions of these activities are discussed in this paper, along with the resulting impact they have had. Through such efforts, undergraduate and graduate students are showing a growing understanding of the relevance of green chemistry in today’s world, with the GCI serving as a platform for similar groups to build upon across Canada.</p