Faculty of Arts and Science

Permanent URI for this communityhttps://hdl.handle.net/1807/16827

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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Application of Direct Analysis in Real Time-Mass Spectrometry (DART-MS) to the study of gas-surface heterogeneous reactions: focus on ozone and PAHs
(ACS Publications, 2015-04-04) Zhou, Shouming; Forbes, Matthew W; Abbatt, Jonathan P D
A novel analytical method is presented whereby Direct Analysis in Real Time-Mass Spectrometry (DART-MS) is applied to the study of gas-surface heterogeneous reactions. To illustrate the capabilities of the approach, the kinetics of a well-studied reaction of surface-bound polycyclic aromatic hydrocarbons with ozone are presented. Specifically, using helium as the reagent gas and with the DART heater temperature of 500 °C, nanogram quantities of benzo[e]pyrene (BeP) deposited on the outside of glass melting point capillary tubes were analyzed in positive ion mode with a limit of detection of 40 pg. Using bis(2-ethylhexyl) sebacate as an internal standard, the kinetics of the ozone-BeP reaction were assessed by determining the surface-bound BeP decays, after oxidation in an off-line reaction cell. The reaction is demonstrated to follow the Langmuir-Hinshelwood mechanism, known to prevail for heterogeneous reactions of this type. In addition, a wide array of oxygenated, condensed-phase products has been observed. The present work demonstrates the capability of the DART-MS technique to investigate the heterogeneous chemistry taking place on a wide range of surfaces, such as those that form in both outdoor and indoor environments.
Epoxide formation from heterogeneous oxidation of benzo[a]pyrene with gas-phase ozone and indoor air
(Royal Society of Chemistry, 2017-08-17) Zhou, Shouming; Yeung, Leo W Y; Forbes, Matthew W; Mabury, Scott; Abbatt, Jonathan P D
The formation of two classes of epoxide products from the heterogeneous reaction of benzo[a]pyrene (BaP) with gas-phase ozone was demonstrated. BaP was coated on a Pyrex glass tube and oxidized with different concentrations of ozone. After oxidation, the epoxide products were derivatized by N-acetylcystein (NAC) and then analyzed by liquid chromatography-tandem mass spectrometry (LC-MS/MS). The results show that in addition to mono-epoxides, diol-epoxides were also formed. BaP exposed to genuine indoor air also produces mono- and diol-epoxides, having similar chromatograms to those produced by oxidation of BaP by low concentrations of ozone. Although it is well recognized that diol-epoxides are formed from BaP oxidation in the human body and that they exhibit carcinogenicity via formation of adducts with DNA, this is the first demonstration that such classes of compounds can be formed by abiotic heterogeneous oxidation.
Evidence for Gas-Surface Equilibrium Control of Indoor Nitrous Acid
(American Chemical Society, 2018-10-11) Collins, Douglas B; Hems, Rachel F; Zhou, Shouming; Wang, Chen; Grignon, Eloi; Alavy, Masih; Siegel, Jeffrey A; Abbatt, Jonathan P D
Nitrous acid (HONO) is an important component of indoor air as a photolabile precursor to hydroxyl radicals and has direct health effects. HONO concentrations are typically higher indoors than outdoors, although indoor concentrations have proved challenging to predict using box models. In this study, time-resolved measurements of HONO and NO2 in a residence showed that [HONO] varied relatively weakly over contiguous periods of hours, while [NO2] fluctuated in association with changes in outdoor [NO2]. Perturbation experiments were performed in which indoor HONO was depleted or elevated and were interpreted using a two-compartment box model. To reproduce the measurements, [HONO] had to be predicted using persistent source and sink processes that do not directly involve NO2, suggesting that HONO was in equilibrium with indoor surfaces. Production of gas phase HONO directly from conversion of NO2 on surfaces had a weak influence on indoor [HONO] during the time of the perturbations. Highly similar temporal responses of HONO and semivolatile carboxylic acids to ventilation of the residence along with the detection of nitrite on indoor surfaces support the concept that indoor HONO mixing ratios are controlled strongly by gas-surface equilibrium.
Exploring Conditions for Ultrafine Particle Formation from Oxidation of Cigarette Smoke in Indoor Environments
(American Chemical Society, 2018-03-30) Wang, Chen; Collins, Douglas B; Hems, Rachel F; Borduas, Nadine; Antiñolo, María; Abbatt, Jonathan P D
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.
Fast oxidation of sulfur dioxide by hydrogen peroxide in deliquesced aerosol particles
(National Academy of Sciences, 2020-01-03) Liu, Tengyu; Clegg, Simon L; Abbatt, Jonathan P D
Atmospheric sulfate aerosols have important impacts on air quality, climate, and human and ecosystem health. However, current air-quality models generally underestimate the rate of conversion of sulfur dioxide (SO2) to sulfate during severe haze pollution events, indicating that our understanding of sulfate formation chemistry is incomplete. This may arise because the air-quality models rely upon kinetics studies of SO2 oxidation conducted in dilute aqueous solutions, and not at the high solute strengths of atmospheric aerosol particles. Here, we utilize an aerosol flow reactor to perform direct investigation on the kinetics of aqueous oxidation of dissolved SO2 by hydrogen peroxide (H2O2) using pH-buffered, submicrometer, deliquesced aerosol particles at relative humidity of 73 to 90%. We find that the high solute strength of the aerosol particles significantly enhances the sulfate formation rate for the H2O2 oxidation pathway compared to the dilute solution. By taking these effects into account, our results indicate that the oxidation of SO2 by H2O2 in the liquid water present in atmospheric aerosol particles can contribute to the missing sulfate source during severe haze episodes.
Indoor Illumination of Terpenes and Bleach Emissions Leads to Particle Formation and Growth
(American Chemical Society, 2019-10-02) Wang, Chen; Collins, Douglas B; Abbatt, Jonathan P D
Application of chlorine bleach solution (major component sodium hypochlorite, NaOCl) in indoor environments leads to the emission of gaseous hypochlorous acid (HOCl) and chlorine (Cl2), both of which are strong oxidants. In contrast to the outdoor atmosphere, where mixing ratios of HOCl and Cl2 tend to be low (10s-100s of ppt), indoor HOCl and Cl2 can reach high levels during cleaning activities (100s of ppb or higher). HOCl and Cl2 may react with unsaturated organic compounds on indoor surfaces and in indoor air. In this study, we studied the reaction of limonene, one of the most common indoor volatile organic compounds (VOCs) arising from use of cleaning products, fragrance, and air fresheners, with HOCl and Cl2 in an environmental chamber. A dark reaction was observed between limonene and HOCl/Cl2 leading to gas-phase reaction products that were investigated using proton transfer reaction mass spectrometry (PTR-MS). With subsequent exposure to indoor fluorescent lights or diffuse sunlight through a nearby window, a substantial mass loading of secondary particles were formed with an averaged mass yield of 40% relative to the amount of limonene consumed. Aerosol mass spectrometry (AMS) measurements indicate a large contribution of particulate chlorine species. Electrospray ionization mass spectrometry (ESI-MS) analysis of filter-collected particles indicates the formation of high molecular weight products. This is the first study of the oxidation of limonene with HOCl and Cl2, and it illustrates the potential for particle formation to occur with indoor lighting during the use of common cleaning products.
Kinetics and Condensed-Phase Products in Multiphase Ozonolysis of an Unsaturated Triglyceride
(American Chemical Society, 2019-10-10) Zhou, Zilin; Zhou, Shouming; Abbatt, Jonathan P D
Ozone is an important oxidant in the environment. To study the nature of multiphase ozonolysis, an unsaturated triglyceride, triolein, of the type present in skin oil, biological membranes, and most cooking oils was oxidized by gas-phase ozone on a surface. A high-performance liquid chromatography/electrospray ionization mass spectrometry (HPLC-ESI-MS) method was developed for analyzing triolein and its oxidized products. Upon exposure to ozone, the decay of thin coatings of triolein was observed, accompanied by the formation of functionalized condensed-phase products including secondary ozonides (SOZ), acids, and aldehydes. By studying the reaction kinetics as a function of average coating thickness and ozone mixing ratio, we determined that the reactive uptake coefficient (γ) is on the order of 10-6 to 10-5. It is also concluded that the reaction occurs in the bulk without a major interfacial component, and the reacto-diffusive depth of ozone in the triolein coating is estimated to be between 8 and 40 nm. The specific nature of the reaction products is affected by the reactions of the Criegee intermediate formed during ozonolysis. In particular, although an increase in the relative humidity to 50% from dry conditions has no effect on the kinetics of triolein decay, the yield of SOZs is significantly depressed, indicating reactions of the Criegee intermediates to form hydroperoxides. Once formed, the SOZ products are thermally stable over periods of at least 48 h at room temperature but decomposition was observed under simulated outdoor sunlight, likely forming organic acids. From an environmental perspective, this chemistry indicates that SOZs and other oxygenates will form via ozonolysis of oily indoor surfaces and skin oil.
Kinetics and Products from Heterogeneous Oxidation of Squalene with Ozone
(ACS Publications, 2016-09-26) Zhou, Shouming; Forbes, Matthew W; Abbatt, Jonathan P D
Motivated by the importance of the heterogeneous chemistry of squalene contained within skin oil to indoor air chemistry, the surface reaction of squalene with gas-phase ozone has been investigated. Using direct analysis in real time mass spectrometry (DART-MS) to monitor squalene, the reactive uptake coefficients were determined to be (4.3 ± 2.2) × 10-4 and (4.0 ± 2.2) × 10-4 for ozone mixing ratios (MRO3) of 50 and 25 ppb, respectively, on squalene films deposited on glass surfaces. At an MRO3 of 25 ppb, the lifetime for oxidation was the same as that in an indoor office with an MRO3 between 22 and 32 ppb, suggesting that O3 was the dominant oxidant in this indoor setting. While the heterogeneous kinetics of squalene and O3 were independent of relative humidity (RH), the RH significantly affected the reaction products. Under dry conditions (<5% RH), in addition to several products between m/z 300 and 350, the major condensed-phase end products were levulinic acid (LLA) and succinic acid (SCA). Under humid conditions (50% RH), the major end products were 4-oxopentanal, 4-oxobutanoic acid, and LLA. The molar yields of LLA and SCA were quantified as 230 ± 43% and 110 ± 31%, respectively, under dry conditions and 91 ± 15% and <5%, respectively, at 50% RH. Moreover, high-molecular weight (molecular weight of >450 Da) products were observed under dry conditions with indications that LLA was involved in their formation. The mechanism of squalene oxidation is discussed in light of these observations, with indications of an important role played by Criegee intermediates.
Organic Surfactants Protect Dissolved Aerosol Components against Heterogeneous Oxidation
(American Chemistry Society, 2019-03-01) Faust, Jennifer A; Abbatt, Jonathan P D
Oxidative aging alters the composition of organic aerosols over time, in turn affecting the ability of aerosols to seed cloud formation and scatter solar radiation. Here we explore the heterogeneous photooxidation of model organic particles with and without a soluble surfactant coating. Tricarballylic acid (TCA), a proxy for α-pinene oxidation products, serves as a representative small organic solute. Sodium dodecyl sulfate (SDS) was selected as the representative soluble surfactant because its surface properties have been extensively characterized. A flow reactor and aerosol mass spectrometer were used to determine the second-order reaction rate constant ( k = (1.9 ± 0.1) × 10-11 cm3 molecule-1 s-1) and reactive uptake coefficient (γ = 3.0) for the heterogeneous photooxidation of uncoated TCA particles by gas-phase OH radicals; such a high uptake coefficient implicates radical chain reactions in the oxidation mechanism. SDS dramatically slows the disappearance of TCA: when the SDS concentration approaches monolayer coverage, the rate of reaction of TCA with OH decreases by ∼60% relative to the rate in the absence of SDS. These results indicate that small concentrations of surface-active molecules on atmospheric particles can protect organic solutes in the bulk from oxidative aging. This effect extends the environmental lifetime of dissolved pollutants.
Role of Aerosol Liquid Water in Secondary Organic Aerosol Formation from Volatile Organic Compounds
(American Chemical Society, 2017-01-26) Faust, Jennifer A; Wong, Jenny P S; Lee, Alex K Y; Abbatt, Jonathan P D
A key mechanism for atmospheric secondary organic aerosol (SOA) formation occurs when oxidation products of volatile organic compounds condense onto pre-existing particles. Here, we examine effects of aerosol liquid water (ALW) on relative SOA yield and composition from α-pinene ozonolysis and the photooxidation of toluene and acetylene by OH. Reactions were conducted in a room-temperature flow tube under low-NOx conditions in the presence of equivalent loadings of deliquesced (∼20 μg m-3 ALW) or effloresced (∼0.2 μg m-3 ALW) ammonium sulfate seeds at exactly the same relative humidity (RH = 70%) and state of wall conditioning. We found 13% and 19% enhancements in relative SOA yield for the α-pinene and toluene systems, respectively, when seeds were deliquesced rather than effloresced. The relative yield doubled in the acetylene system, and this enhancement was partially reversible upon drying the prepared SOA, which reduced the yield by 40% within a time scale of seconds. We attribute the high relative yield of acetylene SOA on deliquesced seeds to aqueous partitioning and particle-phase reactions of the photooxidation product glyoxal. The observed range of relative yields for α-pinene, toluene, and acetylene SOA on deliquesced and effloresced seeds suggests that ALW plays a complicated, system-dependent role in SOA formation.
Selective Uptake of Third-Hand Tobacco Smoke Components to Inorganic and Organic Aerosol Particles
(American Chemical Society, 2018-10-22) Collins, Douglas B; Wang, Chen; Abbatt, Jonathan P D
Third-hand smoke (THS) is an emerging route of exposure to tobacco smoke in the indoor environment. Few studies have investigated the chemical behavior of THS, although initial findings suggest that semivolatile components of THS can partition to indoor aerosol. By exposing single-component particles to THS in an environmental chamber, this study demonstrates a pronounced dependence of THS uptake on aerosol composition. First, it was found that primarily reduced nitrogen compounds (that produced C xH yN z+ ion signal) in THS partitioned strongly to acidic ammoniated sulfate particles, whereas overall THS uptake to more pH-neutral sodium sulfate particles was minimal. Second, THS uptake to pure hydrocarbon particles (squalane) was even greater than to ammoniated sulfate particles with the uptake arising from mainly C xH y compounds. The greater uptake of THS to squalane was mostly driven by the dominant fraction of C xH y compounds in the side stream cigarette smoke aerosol, the composition of which is likely to be broadly similar to THS in these experiments. Third, oxygenated organic particles (sucrose) and solid ammonium sulfate particles showed minimal uptake. These results indicate that particulate THS inhalation exposure will be strongly dependent on the chemical nature of the particles present in the indoor environment.

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