Alam S. Hasson

Production of stabilized Criegee intermediates and peroxides in the gas phase ozonolysis of alkenes: 1. Ethene, trans‐2‐butene, and 2,3‐dimethyl‐2‐butene

Ozone-alkene reactions generate stabilized Criegee intermediates (of the form R1R2COO), which are believed to react with water molecules to form organic hydroperoxides, hydrogen peroxide and carboxylic acids. These reactions are thought to be significant sources of these environmentally important compounds, yet both the yields of stabilized Criegee intermediates and the branching ratios from their reaction with water are not well known. The formation of hydrogen peroxide and organic hydroperoxides was investigated in the gas phase ozonolysis of ethene, trans-2-butene, and 2,3-dimethyl-2-butene for relative humidities (RH) from 0 and 80% by gas chromatography with flame ionization detection and high-performance liquid chromatography with fluorescence detection. Additionally, yields of acetaldehyde and acetic acid from trans-2-butene and acetone from 2,3-dimethyl-2-butene were measured. The reactions of stabilized Criegee intermediates with water were found to proceed almost entirely via organic hydroperoxide or hydrogen peroxide formation with little acid formation. Stabilized Criegee intermediate yields of 0.39, 0.24, and 0.10 were obtained for ethene, trans-2-butene, and 2,3-dimethyl-2-butene, respectively.

An investigation of the relationship between gas-phase and aerosol-borne hydroperoxides in urban air

Abstract Simultaneous measurements of hydroperoxides in both the gas- and the aerosol-phase have been made for the first time. In addition, hydroperoxide levels in the ‘coarse’ (>PM2) and ‘fine’ (PM2) aerosol modes have been characterized. Hydrogen peroxide (H2O2) was found to be the major hydroperoxide present, with trace amounts of methyl hydroperoxide ( CH 3 OOH, MHP ) occasionally being observed. Between May and August 2001, ambient gas- and aerosol-phase hydroperoxide levels were in the range 0.5– 3.5 ppbv , and 0– 13 ng m −3 , respectively. On average, about 40% of aerosol-phase H2O2 was associated with fine particles. The observed aerosol mass loadings correspond to aqueous concentrations of 10−4– 10 −3 M , above the levels necessary to induce lung epithelial cell damage in laboratory studies. The measured H2O2 mass loadings were found to be several times larger than could be explained by the solubility of gaseous H2O2 in liquid water. Potential reasons for this discrepancy are briefly discussed.

(CH3)3COOH (tert-butyl hydroperoxide): OH reaction rate coefficients between 206 and 375 K and the OH photolysis quantum yield at 248 nm

Rate coefficients, k, for the gas-phase reaction of the OH radical with (CH(3))(3)COOH (tert-butyl hydroperoxide) were measured as a function of temperature (206-375 K) and pressure (25-200 Torr (He, N(2))). Rate coefficients were measured under pseudo-first-order conditions using pulsed laser photolysis to produce OH and laser induced fluorescence (PLP-LIF) to measure the OH temporal profile. Two independent methods were used to determine the gas-phase infrared cross sections of (CH(3))(3)COOH, absolute pressure and chemical titration, that were used to determine the (CH(3))(3)COOH concentration in the LIF reactor. The temperature dependence of the rate coefficients is described, within the measurement precision, by the Arrhenius expression k(1)(T) = (7.0 ± 1.0) × 10(-13) exp[(485 ± 20)/T] cm(3) molecule(-1) s(-1) where k(1)(296 K) was measured to be (3.58 ± 0.54) × 10(-12) cm(3) molecule(-1) s(-1). The uncertainties are 2σ (95% confidence level) and include estimated systematic errors. UV absorption cross sections of (CH(3))(3)COOH were determined at 185, 214, 228, and 254 nm and over the wavelength range 210-300 nm. The OH quantum yield following the 248 nm pulsed laser photolysis of (CH(3))(3)COOH was measured relative to the OH quantum yields of H(2)O(2) and HNO(3) using PLP-LIF and found to be near unity.

Branching ratios for the reaction of selected carbonyl-containing peroxy radicals with hydroperoxy radicals.

An important chemical sink for organic peroxy radicals (RO(2)) in the troposphere is reaction with hydroperoxy radicals (HO(2)). Although this reaction is typically assumed to form hydroperoxides as the major products (R1a), acetyl peroxy radicals and acetonyl peroxy radicals have been shown to undergo other reactions (R1b) and (R1c) with substantial branching ratios: RO(2) + HO(2) → ROOH + O(2) (R1a), RO(2) + HO(2) → ROH + O(3) (R1b), RO(2) + HO(2) → RO + OH + O(2) (R1c). Theoretical work suggests that reactions (R1b) and (R1c) may be a general feature of acyl peroxy and α-carbonyl peroxy radicals. In this work, branching ratios for R1a-R1c were derived for six carbonyl-containing peroxy radicals: C(2)H(5)C(O)O(2), C(3)H(7)C(O)O(2), CH(3)C(O)CH(2)O(2), CH(3)C(O)CH(O(2))CH(3), CH(2)ClCH(O(2))C(O)CH(3), and CH(2)ClC(CH(3))(O(2))CHO. Branching ratios for reactions of Cl-atoms with butanal, butanone, methacrolein, and methyl vinyl ketone were also measured as a part of this work. Product yields were determined using a combination of long path Fourier transform infrared spectroscopy, high performance liquid chromatography with fluorescence detection, gas chromatography with flame ionization detection, and gas chromatography-mass spectrometry. The following branching ratios were determined: C(2)H(5)C(O)O(2), Y(R1a) = 0.35 ± 0.1, Y(R1b) = 0.25 ± 0.1, and Y(R1c) = 0.4 ± 0.1; C(3)H(7)C(O)O(2), Y(R1a) = 0.24 ± 0.15, Y(R1b) = 0.29 ± 0.1, and Y(R1c) = 0.47 ± 0.15; CH(3)C(O)CH(2)O(2), Y(R1a) = 0.75 ± 0.13, Y(R1b) = 0, and Y(R1c) = 0.25 ± 0.13; CH(3)C(O)CH(O(2))CH(3), Y(R1a) = 0.42 ± 0.1, Y(R1b) = 0, and Y(R1c) = 0.58 ± 0.1; CH(2)ClC(CH(3))(O(2))CHO, Y(R1a) = 0.2 ± 0.2, Y(R1b) = 0, and Y(R1c) = 0.8 ± 0.2; and CH(2)ClCH(O(2))C(O)CH(3), Y(R1a) = 0.2 ± 0.1, Y(R1b) = 0, and Y(R1c) = 0.8 ± 0.2. The results give insights into possible mechanisms for cycling of OH radicals in the atmosphere.

Method development for the measurement of quinone levels in urine

A method was developed for the quantification of 1-4 ring quinones in urine samples using liquid-liquid extraction followed by analysis with gas chromatography-mass spectrometry. Detection limits for the ten quinones analyzed are in the range 1-2 nmol dm(-3). The potential use of this approach to monitor urinary quinone levels was then evaluated in urine samples from both Sprague-Dawley rats and human subjects. Rats were exposed to 9,10-phenanthraquinone (PQ) by both injection and ingestion (mixed with solid food and dissolved in drinking water). Urinary levels of PQ were found to increase by up to a factor of ten compared to control samples, and the levels were found to depend on both the dose and duration of exposure. Samples were also collected and analyzed periodically from human subjects over the course of six months. Eight quinones were detected in the samples, with levels varying from below the detection limit up to 3 μmol dm(-3).

Performance of commercial nonmethane hydrocarbon analyzers in monitoring oxygenated volatile organic compounds emitted from animal feeding operations

Quantifying non-methane hydrocarbons (NMHC) from animal feeding operations (AFOs) is challenging due to the broad spectrum of compounds and the polar nature of the most abundant compounds. The purpose of this study was to determine the performance of commercial NMHC analyzers for measuring volatile organic compounds (VOCs) commonly emitted from AFOs. Three different NMHC analyzers were tested for response to laboratory generated VOCs, and two were tested in the field at a commercial poultry facility. The NMHC analyzers tested included gas chromatography/flame ionization detector (GC/FID), photoacoustic infrared (PA-IR) and photoionization detector (PID). The GC/FID NHHC analyzer was linear in response to non-polar compounds, but detector response to polar oxygenated compounds were lower than expected due to poor peak shape on the column. The PA-IR NMHC instrument responded well to the calibration standard (propane), methanol, and acetone, but it performed poorly with larger alcohols and ketones and acetonitrile. The PA-IR response varied between compounds in similar compound classes. The PID responded poorly to many of the most abundant VOCs at AFOs, and it underreported alcohols by>70%. In the field monitoring study, total NMHC concentrations were calculated from sum total of VOC determined using EPA Methods TO-15 and TO-17 with GC-MS compared to results from NMHC analyzers. NMHC GC/FID values were greater than the values calculated from the individual compound measurements. This indicated the presence of small hydrocarbons not measured with TO-15 or TO-17 such as propane. The PA-IR response was variable, but it was always lower than the GC/FID response. Results suggest that improved approaches are needed to accurately determine the VOC profile and NMHC emission rates from AFOs. Implications: Commercial nonmethane hydrocarbons (NMHC) analyzers that monitor volatile organic compounds (VOCs) will underreport true concentrations of VOCs if the compound profiles have significant levels of polar compounds. Laboratory experiments showed that the commercial instruments accurately measured nonpolar compounds, but polar compounds were being underreported by NMHC analyzers with known standards. Field experiments showed that laboratory instruments underreported true concentration in the field due to the fact that the most abundant NMHC associated with animal feeding operations were polar VOCs. This report recommends not using NMHC analyzers for quantifying VOCs at animal feeding operations.