Kinetic and mass-spectrometric studies of atmospherically relevant mercury-bromine chemistry Elise-Andrée Guérette Department of Chemistry McGill University Montréal, Québec, Canada October 2010 A thesis submitted to McGill University in partial fulfilment of the require­ ments of the degree of Master of Science ©Elise-Andrée Guérette, 2010. All Rights Reserved. Acknowledgements My thanks go out to Dr. Daniel Deeds for his help with everything having to do with atmospheric pressure chemical ionization mass spectrometry. Working with you was always a pleasure. Alain Tessier from CBAMS at Concordia Univer­ sity was immensely helpful and creative in his problem solving. Thanks also to Graydon Snider for helpful discussions and helping me get started with the kinetic work. Edward Hudson, Nermin Eltouny, Daniel Deeds, Graydon Snider and Ma­ hamud Subir all proofread this thesis and provided helpful comments. I would also like to extend grateful thanks to my supervisor, Parisa Ariya, for her understanding and patience, and for providing me with this opportunity. Thanks also for reading this thesis before its submission and for providing valu­ able comments. Fred Kluck, Rick Rossi and George Kopp from the Department of Chemistry deserve mention for their help building and repairing things, often at short notice. Thanks also to FQRNT, the Department of Chemistry at McGill, and the Dr. and Mrs. Milton Leong fund for providing personal financial assistance during the course of my studies. Thanks last, but perhaps most of all, to my spouse, Craig Titchener, who stood by me every step of the way. Thank you. II Abstract Bromine radicals are thought to play an important role in the chemistry of atmospheric elemental mercury, however uncertainties remain concerning the rate and the mechanism of the reaction. The products of the atmospheric reaction are thought to be mercury halides of the form HgBrX, where X = Cl, Br, I. This thesis describes the early stages of development of a methodology for the detection of atmospheric mercury halides by Atmospheric Pressure Chem­ ical Ionisation Mass Spectrometry (APCI-MS). It also reports the results of labor­ atory experiments aimed at identifying the product(s) and determining the rate coefficient of the reaction at near atmospheric conditions. The kinetics were studied using the relative rate method with 1-butene as the reference molecule and / k k − the value of the Hg Br 1 C 4 H 8 Br ratio was mapped for a wide variety of ex­ perimental conditions. The experiments confirm the lack of oxygen dependence of the mercury reaction. A rate coefficient of (3.1 ± 1.9) x 10-13 cm3 molecule-1 s-1 was obtained, which is in agreement with the most recent peer-reviewed study. Using solid- phase micro-extraction (SPME) in the gas phase, HgBr2 was confirmed as one of the end products of the mercury reaction under our laboratory conditions, and two products of the 1-butene reaction (1-bromo-2-butanone and 1-bromo-2-butanol) were also identified for the first time. III Résumé Les radicaux de brome jouent potentiellement un rôle important dans la chimie atmosphérique du mercure élémentaire, mais la vitesse ainsi que le méca­ nisme de la réaction demeurent incertains. Dans l'atmosphère, les produits de la réactions sont probablement des halogénures de mercure de la forme HgBrX (X = Cl, Br, I). Ce mémoire décrit les premiers stades de développement d'une méthode pour la détection des halogénures de mercure dans l'air par ionisation chimique à pression atmosphérique et spectrométrie de masse (APCI-MS). Les résultats d'ex­ périences de laboratoire visant l'identification du ou des produits de la réaction ainsi que la détermination de sa constante de vitesse sous des conditions quasi-at­ mosphériques sont aussi présentés. La méthode des vitesses relatives a été utilisé pour étudier la cinétique de la réaction. Le 1-butène était la molécule de référence. / k k − Le ratio des constantes de vitesse, Hg Br 1 C 4 H 8 Br , a été déterminé sous des conditions variées. Les résultats confirment que la vitesse de réaction ne dépend pas sur la pression partielle d'oxygène dans le système. Une constante de vitesse de (3.1 ± 1.9) x 10-13 cm3 molécule-1 s-1 a été obtenue. Ce résultat est comparable à ceux pu­ bliés par d'autres groupes récemment. La micro-extraction sur phase solide a per­ mis de confirmer que HgBr2 est l'un des produits finaux de la réaction sous nos conditions expérimentales. Deux produits de la réaction entre les radicaux de brome et le 1-butène, le 1-bromobutan-2-one et le 1-bromobutan-2-ol, ont aussi été identifiés pour la première fois. IV Table of Contents 1 Introduction......................................................................................................1 1.1 Background ..............................................................................................1 1.1.1 Mercury – The Element ...................................................................1 1.1.2 Mercury throughout History.............................................................2 1.1.2.1 Mercury and the Ancients ........................................................2 1.1.2.2 Alchemy....................................................................................5 1.1.2.3 Mercury in Medicine ................................................................5 1.1.2.4 Mercury in Scientific Discovery...............................................8 1.1.2.5 Mercury as a Commodity..........................................................9 1.1.2.6 Modern stance – Mercury as a global pollutant .....................11 1.2 Atmospheric chemistry of mercury .......................................................12 1.2.1 Analytical methods for the determination of atmospheric mercury14 1.2.1.1 Current methods .....................................................................14 1.2.1.2 Potential methods ...................................................................20 1.2.2 Pathways for the chemical formation of gaseous oxidized mercury (GOM)......................................................................................................22 1.2.2.1 Chemical transformation of GEM: insights from field data...22 1.2.2.2 Chemical transformation of GEM: insights from laboratory- based experiments...............................................................................23 1.2.2.3 The homogeneous gas-phase reaction of elemental mercury and bromine radicals Hg0 + Br· ↔ HgBr...........................................28 1.3 Objectives ..............................................................................................31 2 Methodology..................................................................................................32 2.1 Method development for the determination of mercury halides in ambient air through atmospheric chemical ionization mass spectrometry (APCI-MS) analysis.....................................................................................32 2.1.1 Preliminary tests .............................................................................33 2.1.2 Gold solid-phase micro-extraction (Au-SPME).............................34 V 2.1.2.1 Modification of the original APCI probe for SPME desorption .............................................................................................................35 2.1.2.2 Sampling device - Au-SPME..................................................36 2.2 Homogeneous gas-phase reaction of elemental mercury and bromine radicals: product and kinetic studies ............................................................37 2.2.1 General considerations ...................................................................37 2.2.1.1 Experimental set-up.................................................................38 2.2.1.2 Preparation of the reactant mixtures .......................................40 2.2.2 Detection of reaction products using solid-phase micro-extraction (SPME)....................................................................................................42 2.2.2.1 Solid-phase micro-extraction coupled with electron impact mass spectrometry (SPME-GC-EI-MS) .............................................42 2.2.3 Kinetics studies ..............................................................................45 2.2.3.1 Methodology – the relative rate method ...............................45 2.2.3.2 Chemical Analysis: Kinetic experiments................................46 2.2.3.3 Preliminary tests .....................................................................47 2.2.3.4 Initial slope experiments ........................................................50 2.2.3.5 Error analysis ..........................................................................50 2.3 Materials & Supplies..............................................................................52 3 Results and Discussion...................................................................................53 3.1 General considerations............................................................................53 3.2 Method development for the determination of mercury halides in ambient air through atmospheric chemical ionization mass spectrometry (APCI-MS) analysis.....................................................................................54 3.2.1 Preliminary tests..............................................................................54 3.2.2 Gold solid-phase micro-extraction (Au-SPME) results..................55 3.2.3 Reducing unfavourable ions reactions in the