Faculty of Arts and Science

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Since the first classics, chemistry, philosophy and physics classes were taught at King’s College — U of T’s precursor — in 1843, the Faculty of Arts & Science has evolved into one of the most comprehensive and diverse academic divisions in North America and established itself as the heart of one of the world’s leading universities. Home to the majority of undergraduates on the St. George campus, Arts & Science offers an unparalleled breadth of programs leading to bachelor’s degrees in arts, science and commerce.

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Browsing Faculty of Arts and Science by Author "Abbatt, Jonathan P.D."

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    An Experimental Assessment of the Importance of S(IV) Oxidation by Hypohalous Acids in the Marine Atmosphere
    (Wiley, 2020-02-10) Liu, Tengyu; Abbatt, Jonathan P.D.
    Atmospheric aerosol particles contribute to the direct and indirect forcing of the Earth's climate. A large portion of aerosol particle mass is sulfate, formed from chemical reactions involving the oxidation of sulfur dioxide. Significant uncertainties in assessing global radiative forcing arise from uncertainties in the formation mechanisms of sulfate aerosols in the marine atmosphere. Model studies have suggested that aqueous oxidation of sulfur dioxide by hypochlorous and hypobromous acids plays an important role in sulfate production in the marine atmosphere. However, the validity of these model studies remains uncertain because the reaction rate constants of two key reactions—hypochlorous and hypobromous acids reacting with bisulfite—have never been experimentally measured. Here, we show with laboratory experiments that the reaction rate constant of hypochlorous acid with bisulfite is 3 orders of magnitude lower than that used in atmospheric models. A simple chemical kinetics model predicts that the reaction rate constant of hypobromous acid with bisulfite is 2 orders of magnitude lower than the value assumed in atmospheric models. As a result, sulfate production via the hypochlorous acid pathway in the marine atmosphere may not be as important as previously believed, while sulfate production through hypobromous acid reactions remains atmospherically important.
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    Ice nucleating behavior of different tree pollen in the immersion mode
    (Elsevier, 2020-04-11) Gute, Ellen; Abbatt, Jonathan P.D.
    Biological particles, including pollen, are released into the atmosphere in large amounts and carry components which can initiate ice nucleation (IN) under cloud conditions. In this study, we investigate in immersion mode the ice nucleation ability of eleven different tree pollen from deciduous and evergreen trees. Droplet freezing experiments are conducted, where we find the IN ability of filtered tree pollen aqueous suspensions to vary over more than 10 °C and ice nucleation to be triggered by subpollen particles that are smaller than 0.45 μm in size. The presence of full pollen grains in the sample does not significantly change the median freezing temperature. The IN activity of the pollen samples is complemented by total organic carbon (TOC) analysis, which allows calculation of the number of ice nucleating particles per mass of carbon. Infrared analysis of the bulk samples does not clearly indicate whether specific functional groups are correlated to the ability of the subpollen particles to nucleate ice.
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    Suppression of OH Generation from the Photo-Fenton Reaction in the Presence of α-Pinene Secondary Organic Aerosol Material
    (ACS Publications, 2017-09-19) Hems, Rachel F.; Hsieh, Jeremy S.; Slodki, Mark A.; Zhou, Shouming; Abbatt, Jonathan P.D.
    Although Fenton and Photo-Fenton chemistry is thought to be an important source of OH in cloud and fog water, a high dissolved organic content, especially of secondary organic aerosol (SOA) material, may affect the production of OH via this mechanism. The relative production of OH was measured for Fenton and Photo-Fenton reactions with H2O2 and Fenton-like and Photo-Fenton-like reactions with α-pinene ozonolysis SOA material, under cloud water relevant conditions (5 μM iron, 45 μM H2O2, and 1500 μM SOA). It is demonstrated that the generation of OH radicals from Photo-Fenton chemistry can be significantly suppressed by addition of α-pinene SOA material, where the OH yield for solutions containing H2O2 and SOA material together was decreased by a factor of 6 compared to that when only H2O2 was present, likely because of complexation by carboxylic acids (such as pinonic acid). When SOA is examined without additional H2O2 present, OH is generated by Photo-Fenton chemistry but at a rate lower than that for Photo-Fenton chemistry with H2O2 alone. Without taking into account the suppression by SOA material, one may overestimate the generation of OH by Photo-Fenton chemistry. Furthermore, the suppression of Photo-Fenton chemistry in aqueous organic aerosol may be enhanced by a higher SOA material concentration.