Kinetics and Condensed-Phase Products in Multiphase Ozonolysis of an Unsaturated Triglyceride.

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.

Organic Peroxides and Sulfur Dioxide in Aerosol: Source of Particulate Sulfate.

Sulfur oxides (SO) are important atmospheric trace species in both gas and particulate phases, and sulfate is a major component of atmospheric aerosol. One potentially important source of particulate sulfate formation is the oxidation of dissolved SO by organic peroxides, which comprises a major fraction of secondary organic aerosol (SOA). In this study, we investigated the reaction kinetics and mechanisms between SO and condensed-phase peroxides.

Multiphase reactivity of polycyclic aromatic hydrocarbons is driven by phase separation and diffusion limitations.

Benzo[a]pyrene (BaP), a key polycyclic aromatic hydrocarbon (PAH) often associated with soot particles coated by organic compounds, is a known carcinogen and mutagen. When mixed with organics, the kinetics and mechanisms of chemical transformations of BaP by ozone in indoor and outdoor environments are still not fully elucidated. Using direct analysis in real-time mass spectrometry (DART-MS), kinetics studies of the ozonolysis of BaP in thin films exhibited fast initial loss of BaP followed by a slower decay at long exposure times.

Sources of isocyanic acid (HNCO) indoors: a focus on cigarette smoke.

The sources and sinks of isocyanic acid (HNCO), a toxic gas, in indoor environments are largely uncharacterized. In particular, cigarette smoke has been identified as a significant source. In this study, controlled smoking of tobacco cigarettes was investigated in both an environmental chamber and a residence in Toronto, Canada using an acetate-CIMS.

Heterogeneous Chlorination of Squalene and Oleic Acid.

Washing with chlorine bleach leads to high mixing ratios of gas-phase HOCl. Using two methods that are sensitive to surface film composition-attenuated total reflection fourier transform infrared (ATR-FTIR) spectroscopy and direct analysis in real time mass spectrometry (DART-MS)-we present the first study of the chlorination chemistry that occurs when gaseous HOCl reacts with thin films of squalene and oleic acid. At mixing ratios of 600 ppbv, HOCl forms chlorohydrins by adding across carbon-carbon double bonds without breaking the carbon backbone.

Evidence for Gas-Surface Equilibrium Control of Indoor Nitrous Acid.

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 NO in a residence showed that [HONO] varied relatively weakly over contiguous periods of hours, while [NO] fluctuated in association with changes in outdoor [NO].

Epoxide formation from heterogeneous oxidation of benzo[a]pyrene with gas-phase ozone and indoor air.

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).

Kinetics and Products from Heterogeneous Oxidation of Squalene with Ozone.

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.

Formation of environmentally persistent free radicals from the heterogeneous reaction of ozone and polycyclic aromatic compounds.

In the 1980s long-lived radical species were identified in cigarette tar. Since then, environmentally persistent free radicals (EPFRs) have been observed in ambient particulate matter, and have been generated in particulate matter generated from internal combustion engines. For the first time, we measure in situ the formation and decay of EPFRs through the heterogeneous reaction of ozone and several polycyclic aromatic compounds (PAC).

Connecting the oxidation of soot to its redox cycling abilities.

Although it is known that soot particles are emitted in large quantities to the atmosphere, our understanding of their environmental effects is limited by our knowledge of how their composition is subsequently altered through atmospheric processing. Here we present an on-line mass spectrometric study of the changing chemical composition of hydrocarbon soot particles as they are oxidized by gas-phase ozone, and we show that the surface-mediated loss rates of adsorbed polycyclic aromatic hydrocarbons in soot are directly connected to a significant increase in the particle redox cycling abilities. With redox cycling implicated as an oxidative stress mechanism that arises after inhalation of atmospheric particles, this work draws a quantitative connection between the detailed heterogeneous chemistry occurring on atmospheric particles and a potential toxic mechanism attributable to that aerosol.

Application of Direct Analysis in Real Time-Mass Spectrometry (DART-MS) to the study of gas-surface heterogeneous reactions: focus on ozone and PAHs.

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.

Changes in secondary organic aerosol composition and mass due to photolysis: relative humidity dependence.

This study is focused on the relative humidity (RH) dependence of water-soluble secondary organic aerosol (SOA) aging by photolysis. Particles containing α-pinene SOA and ammonium sulfate, generated by atomization, were exposed to UV radiation in an environmental chamber at three RH conditions (5, 45, and 85%), and changes in chemical composition and mass were monitored using an aerosol mass spectrometer (AMS). Under all RH conditions, photolysis leads to substantial loss of SOA mass, where the rate of mass loss decreased with decreasing RH.

Kinetic limitations in gas-particle reactions arising from slow diffusion in secondary organic aerosol.

The potential for aerosol physical properties, such as phase, morphology and viscosity/ diffusivity, to affect particle reactivity remains highly uncertain. We report here a study of the effect of bulk diffusivity of polycyclic aromatic hydrocarbons (PAHs) in secondary organic aerosol (SOA) on the kinetics of the heterogeneous reaction of particle-borne benzo[a]pyrene (BaP) with ozone. The experiments were performed by coating BaP-ammonium sulfate particles with multilayers of SOA formed from ozonolysis of alpha-pinene, and by subsequently investigating the kinetics of BaP loss via reaction with excess ozone using an aerosol flow tube coupled to an Aerodyne Aerosol Mass Spectrometer (AMS).

Kinetic study of gas-phase reactions of OH and NO3 radicals and O3 with iso-butyl and tert-butyl vinyl ethers.

Using a relative rate technique, kinetic studies on the gas-phase reactions of OH radicals, ozone, and NO(3) radicals with iso-butyl vinyl ether (iBVE) and tert-butyl vinyl ether (tBVE) have been performed in a 405 L Duran glass chamber at (298 ± 3) K and atmospheric pressure (750 ± 10 Torr) in synthetic air using in situ FTIR spectroscopy to monitor the reactants. The following rate coefficients (in units of cm(3) molecule(-1) s(-1)) have been obtained: (1.08 ± 0.

Evaluation of the effects of ozone oxidation on redox-cycling activity of two-stroke engine exhaust particles.

The effect of oxidation on the redox-cycling activity of engine exhaust particles is examined. Particles obtained from a two-stroke gasoline engine were oxidized in a flow tube with ozone on a one-minute time scale both in the presence and absence of substantial gas-phase exhaust components. Whereas ozone concentrations were high, the ozone exposures were approximately equivalent to 60 ppb ozone for 2-8 h.

Rate coefficients for the gas-phase reactions of OH and NO3 radicals and O3 with ethyleneglycol monovinyl ether, ethyleneglycol divinyl ether, and diethyleneglycol divinyl ether.

Kinetic studies have been performed on the reactions of OH and NO(3) radicals and ozone with three ethyleneglycol vinyl ethers (EGVEs), that is, ethyleneglycol monovinyl ether (EGMVE, HOCH(2)CH(2)OCH=CH(2)), ethyleneglycol divinyl ether (EGDVE, H(2)C=CHOCH(2)CH(2)OCH=CH(2)), and diethyleneglycol divinyl ether (DEGDVE, H(2)C=CHOCH(2)CH(2)OCH(2)CH(2)OCH=CH(2)). Using a relative rate technique, rate coefficients have been determined for the reactions in a 405 L borosilicate glass chamber at (298 +/- 3) K in one atmosphere of synthetic air using in situ FTIR spectroscopy to monitor the reactants. The following rate coefficients (in units of cm(3) molecule(-1) s(-1)) were obtained: (1.

Atmospheric chemistry of acetylacetone.

A kinetic study on the reactions of the OH radical and ozone with acetylacetone (AcAc) has been performed in a 1080 L quartz glass reaction chamber using in situ FTIR spectroscopy analysis. Temperature dependent rate coefficients for the reaction of AcAc with the OH radical were determined over the temperature range 285-310 K using the relative kinetic method. The following Arrhenius expression was derived: k = 3.

Investigations on the gas-phase photolysis and OH radical kinetics of methyl-2-nitrophenols.

Methyl-2-nitrophenols can be emitted directly to the atmosphere or can be formed in situ via the oxidation of aromatic hydrocarbons. Nitrophenols possess phytotoxic properties and recent studies indicate their photooxidation is effective in producing secondary organic aerosols. Therefore, investigations on the major photooxidation pathways of these compounds with respect to assessing their environmental impacts and effects on human health are highly relevant.

Product study of the OH, NO3, and O3 initiated atmospheric photooxidation of propyl vinyl ether.

A product study is reported on the gas-phase reactions of OH and NO3 radicals and ozone with propyl vinyl ether (PVE). The experiments were performed in a 405 L borosilicate glass chamber in synthetic air at 298 +/- 3 K using long path in situ FTIR spectroscopy for the analysis of the reactants and products. In the presence of NO(x) (NO + NO2) the main products for the OH-radical initiated oxidation of PVE were propylformate and formaldehyde with molar formation yields of 78.

Kinetic study of the gas-phase reactions of OH and NO3 radicals and O3 with selected vinyl ethers.

Kinetic studies on the gas-phase reactions of OH and NO3 radicals and ozone with ethyl vinyl ether (EVE), propyl vinyl ether (PVE) and butyl vinyl ether (BVE) have been performed in a 405 L borosilicate glass chamber at 298 +/- 3 K in synthetic air using in situ FTIR spectroscopy to monitor the reactants. Using a relative kinetic method rate coefficients (in units of cm3 molecule(-1) s(-1)) of (7.79 +/- 1.