Title Chamber investigations of atmospheric mercury oxidation chemistry Author(s) Darby, Steven B. Publication date 2015 Original citation Darby, S. B. 2015. Chamber investigations of atmospheric mercury oxidation chemistry. PhD Thesis, University College Cork. Type of publication Doctoral thesis Rights © 2015, Steven B. Darby http://creativecommons.org/licenses/by-nc-nd/3.0/ Item downloaded http://hdl.handle.net/10468/2076 from Downloaded on 2017-09-05T01:12:52Z Chamber investigations of atmospheric mercury oxidation chemistry Steven Ben Darby ¡ NATIONAL UNIVERSITY OF IRELAND, CORK FACULTY OF SCIENCE DEPARTMENT OF CHEMISTRY Thesis submitted for the degree of Doctor of Philosophy January 2015 Head of Department: Prof Martyn Pemble Supervisor: Dr Dean Venables Contents Contents List of Figures . iv List of Tables . ix Acknowledgements . xi Abstract . xii 1 Introduction 1 1.1 Background . .1 1.2 Mercury as a toxin . .2 1.2.1 Mechanism of toxicity . .3 1.2.2 Minamata . .4 1.2.3 Iraq . .4 1.2.4 Hg Regulation . .5 1.3 Sources and Sinks . .6 1.4 Mercury the element . .9 1.4.1 Mercury Detection . 11 1.4.2 Environmental Chemistry . 12 1.4.3 Mercury Depletion Events . 13 1.5 Units used in this thesis . 14 2 Development of atmospheric mercury detectors 15 2.1 Atmospheric mercury measurement techniques . 16 2.1.1 Detection of GEM . 16 2.1.2 Detection of RGM . 19 2.1.3 Detection of PHg . 21 2.2 Flux measurement techniques . 21 2.2.1 Dynamic Flux Chamber . 22 2.2.2 Micrometeorological Methods . 22 2.2.3 Differential absorption LIDAR . 23 2.2.4 Radon Flux Correlation . 23 2.3 Instrument Development . 24 2.3.1 Laser system . 24 2.3.2 Frequency control . 26 2.3.3 Laser performance . 27 2.3.4 Sum Frequency Generation . 31 2.4 Cavity Enhanced Absorption Spectroscopy . 32 2.4.1 Experimental . 34 2.4.2 Results and Discussion . 35 2.4.3 Application to other gases . 39 2.4.4 Summary . 40 2.5 Conclusions . 41 3 Chamber setup for study of mercury oxidation kinetics 42 3.1 Introduction . 42 3.1.1 Mercury Chamber Studies . 43 3.2 Chamber Description . 44 i Contents 3.2.1 Chamber cooling . 45 3.2.2 Volume determination and flush rate . 46 3.2.3 Mixing time . 48 3.2.4 Wall Losses . 48 3.2.5 Reagent introduction . 50 3.3 Cavity Enhanced Absorption Spectrometers . 52 3.3.1 Cavity enhancement factor calibration . 55 3.3.2 Retrieving [Br2] ........................... 59 3.3.3 [Br2] Artefacts . 61 3.4 Origin of the temperature-induced artefact . 63 3.4.1 Temperature stability of CEAS system . 64 3.4.2 Reproducing the artefact . 70 3.5 Photolytic flux measurement . 72 3.5.1 Observation of [Br2] under photolysis . 72 3.5.2 Standard reaction . 74 3.5.3 Calibrated spectroradiometer . 75 3.6 Experimental procedure . 78 3.6.1 Chamber preparation . 78 3.6.2 Typical experiment . 79 3.6.3 Injection sequence . 79 3.7 Uncertainty Budget . 80 3.7.1 Calibration . 80 3.7.2 Br2 Injection . 80 3.7.3 Br2 Retrieval . 81 3.7.4 Wall loss . 82 3.7.5 Hg Concentrations . 82 4 Chamber results 83 4.1 Overview of chemical kinetics . 83 4.2 Review of rates . 84 4.2.1 Br source . 87 4.2.2 Oxidation of Hg . 88 4.2.3 Reduction of HgBr . 89 4.2.4 Oxidation of Hg(1+)........................ 90 4.2.5 Reactions involving Oxygen . 91 4.2.6 Other reactions . 93 4.3 Simulation of chamber results . 101 4.4 Reactions in the dark . 102 4.4.1 Data Analysis . 102 4.4.2 Photolysis from LEDs and laser . 106 4.4.3 Surface reaction . 107 4.4.4 Dark reaction in the presence of amylene . 109 4.4.5 Temperature effect on dark reaction . 110 4.4.6 Source of Dark reaction . 111 4.5 Reactions under illumination . 113 4.5.1 Data analysis . 113 ii Contents 4.5.2 Temperature effect on illuminated reaction . 115 4.5.3 NOx ................................... 117 4.5.4 BrO . 118 4.5.5 Reactions with larger surface area . 120 4.5.6 Sea Salt Aerosol . 120 4.5.7 Reactions in contaminated air . 122 4.6 Fate of Reaction Products . 124 4.6.1 Scavenge from chamber air . 124 4.6.2 Heating walls . 125 4.6.3 Swabbing walls . 125 4.7 Analysis of whole Hg decay profile . 125 4.7.1 Order in Hg . 125 4.7.2 Simulation of whole decay curve . 126 4.7.3 Influence of each parameter . 128 4.7.4 Reactions under illumination . 132 4.7.5 Order of reaction in Br2 . 134 4.7.6 Reaction in the dark . 138 4.7.7 Conclusions . 140 4.8 Application to environmental studies . 141 5 Conclusions and Further Work 143 5.1 Hg Detector . 143 5.1.1 Future Work . 143 5.2 Hg Chamber Reactions . 144 5.2.1 Main Results . 144 5.2.2 Future work . 146 iii List of Figures List of Figures 1.1 The global mercury budget. Total inventories (numbers in white 1 boxes) are in Mg, and fluxes in Mg yr− . The percentage values in brackets are the estimated increases in inventories in the past 100 years due to anthropogenic activities. Image taken from the Technical Background to the Global Mercury Assessment, UNEP. 1 ........7 1.2 [Hg] with ice depth in a North American glacier. Image from the Global Mercury Assessment, UNEP. 2 ....................8 2.1 Optical design of the proposed Hg monitoring instrument. 25 2.2 Photograph of the ECDL in operation. Laser diode is on right, grating and beam steering mirror in centre and tuned wavelength output on left. 28 2.3 Highly dispersed modes of the ECDL projected onto a fluorescent screen. Contrast and brightness are adjusted to see modes more clearly. Scale in cm. 28 2.4 ECDL emission spectrum at 120 mA injection current and 30 mW output power, showing 16 dominant modes spread over 1 nm. 29 2.5 (a) Free running diode emission with no feedback grating or lens at different currents. (b) Diode emission at 41 mA, showing close to SLM operation. 29 2.6 (a) Diode emission with a collimating lens at a range of currents. (b) Diode emission at 44 mA, showing close to SLM operation. 30 2.7.