Browsing by Subject "Chlorine"

Now showing 1 - 4 of 4

Absorption of chlorine and mercury in sulfite solutions
(2002-08) Roy, Sharmistha; Rochelle, Gary T.
Halogen chemistry and stable chlorine isotope composition of thermal springs and arc lavas in the Cascade arc
(2013-08) Cullen, Jeffery Todd; Barnes, Jaime Danielle
The stable isotope compositions (chlorine, oxygen, and hydrogen), major anion concentrations, and major/minor cation concentrations of 37 thermal (any spring water with temperature at least 6.5° C above mean ambient air temperature) and mineral springs from the Cascade volcanic arc system were measured in order to better determine chlorine sources within the Cascades hydrothermal systems, and thus place better constraints on halogen flux through the subduction zone. Typically, most subduction zone flux calculations have been limited to the study of the erupted magmas and gases from fumarole vents, yet magmatic discharge through thermal springs may be considerable, particularly those in the often ignored forearc. Additionally, 9 geochemically well characterized lavas from across the Mt. St. Helens/Mt. Adams region of the Cascade arc (Leeman et al. 2001, 2005) were analyzed for their halogen concentrations, as well as their Cl stable isotope composition. Cl concentrations in the thermal springs range from 6 to 13,850 ppm and have δ37Cl values that range from -0.1‰ to + 1.9‰ (average = +0.8 ± 0.4‰; error = ± 0.2‰), with no systematic variation along or across the arc. The slightly positive values (~0.0 to +0.9‰) may be explained by fluid-rock interaction with underlying lithologic units, such as 37Cl-enriched volcanic sequences, and/or serpentinites or oceanic crust of accreted oceanic terranes. Another process possibly contributing to these positive δ37Cl values, particularly those with δ37Cl > 1‰, is magmatic HCl fractionation during degassing generating an enriched 37Cl vapor which mixes with thermal waters. We cannot completely rule out slab-derived altered oceanic crustal chlorine that has degassed into the springs, although most slab Cl is believed to have already been devolatilized from the slab before reaching sub-arc depths corresponding to longitudes where these springs are located at the surface. Lavas from the Columbia transect across the arc exhibit highest Cl concentrations at the volcanic front compared to the forearc and backarc. Br, like Cl, exhibits highest concentrations along the volcanic front. F and I show a progressive decrease in concentration from forearc to backarc which may demonstrate the putative early surge of fluids/fluid mobile element loss early in subduction at relatively shallow depth. δ37Cl values range from -0.1 to +0.8‰ (error = ± 0.2‰) and may reflect a component of assimilation of crustal material, or is derived from an enriched mantle, although we cannot completely rule out some isotopic fractionation and/or slab-derived chlorine.
Particulate matter formation from volatile chemical products including combustion and non-combustion sources
(2018-10-09) Dhulipala, Surya Venkatesh; Hildebrandt Ruiz, Lea; Corsi, Richard; Allen, David; Rochelle, Gary; Xu, Ying
New evidence on the contribution of volatile chemical products from non-combustion sources to ambient particulate matter formation has renewed interest in policy-makers and atmospheric scientists to quantify these emissions which have historically been under-reported. In this dissertation, several representative compounds are chosen to provide a holistic comparison of particulate matter formation from both combustion and non-combustion sources. For this purpose, an environmental chamber is employed with state-of-art-instruments to monitor the formation and decay of air pollutants in the gas-phase and particle-phase. The Aerosol Chemical Speciation Monitor (ACSM) is used to measure the total concentration and bulk composition of particulate matter less than 1 µm in size (PM₁). The High Resolution Time-of-Flight-Mass-Spectrometer (HR-Tof-CIMS) along with a Filter Inlet for Aerosols and Gases (FIGAERO) is used to measure the gas-phase composition in real-time and the particle-phase composition in a semi-continuous manner. Toluene, an aromatic compound, is commonly used in solvents. Its reaction with OH radicals, the most abundant radical in the atmosphere, is well understood but its reaction with chlorine radicals is not. Chlorine is an important oxidant in both in-land and coastal areas. Here, high oxidative states of organic aerosol (component of PM) and gas-phase products formed during toluene-Cl photo-oxidation are reported. Secondary OH radical production is also observed. Long-chain alkanes are associated with vehicular exhaust and their reactions with chlorine also remain poorly understood. Here, the Cl-initiated photo-oxidation of alkanes with 10 carbons – n-decane, 2-methyl nonane and butyl cyclohexane are reported under low NO [subscript x] environments and variable relative humidity (0% and 35-55%). Presence of gas-phase and particle-products associated with OH radical chemistry are reported in the presence of chlorine. A class of compounds defined as Low Vapor Pressure Volatile Organic Compounds (LVP-VOCs) by policy-makers and referred to as Intermediate-Volatility Organic Compounds (IVOCs) by atmospheric scientists includes commercial grade mineral spirits, diethylene mono butyl glycol ether (DEGBE) and Texanol®, which are commonly used in solvents and coatings. Here, the Cl- and OH-radical initiated particulate matter formation from these IVOCs are discussed and compared to alkanes of similar volatility but originating from a combustion source (n-pentadecane and 2,6,10 trimethyl dodecane).
The behavior of halogens (F, Cl, Br, I) in altered oceanic crust during prograde subduction zone metamorphism and devolatilization
(2022-05-05) Beaudoin, Grace Margaret; Barnes, Jaime Danielle; Lassiter, John C; John, Timm; Penniston-Dorland, Sarah; Stockli, Daniel F
Halogens (F, Cl, Br, I) are volatile elements enriched in Earth’s surface reservoirs. Following seafloor alteration and tectonic convergence, halogens are carried into subduction zones. Prograde metamorphism of altered ocean crust (AOC) results in hydrous mineral breakdown and the release of volatiles. Halogen devolatilization is not well constrained, particularly for Br and I. To explore the halogens fluxes and behaviors during subduction of AOC, this study investigates bulk rock concentrations from seafloor AOC drill cores (n=21) and paleo-subduction settings that expose exhumed metamorphic rocks (n=44) that record the chemical evolution of AOC during prograde metamorphism. Chapter 2 juxtaposes eclogitic and AOC samples to gauge broadscale changes to the halogen budget between the trench and the depths of ~80 km. Chapter 3 focuses on a suite of petrogenetically-related meta-ophiolites from the Western Alps that record progressive metamorphism and shed light on halogen loss across metamorphic grade, especially at low P-T conditions. To study how halogens partition during phase breakdown and fluid transport, Chapter 4 examines a ~1 m transect of eclogitic samples that preserve evidence of high pressure vein formation and fluid-rock interactions. Findings from this work reveal that halogens are not evenly distributed in AOC. Basalts are F-rich and gabbros are Cl- and Br-rich. During subduction, F is decoupled from the heavy halogens (Cl, Br, I) displaying compatibility and immobility. Chlorine and Br are closely coupled; they preferentially partition into fluid phases and are efficiently removed from the mafic slab. Iodine behaviors are more cryptic, with many high-P samples preserving protolith-level abundances. Halogen mobility in devolatilizing AOC is as follows: Cl ≈ Br > I ≫ F. New flux estimates find that ≤40% of initial F and I and ~70% of initial Cl and Br is removed from subducting AOC prior to depths of arc magma genesis, with much of this loss occurring early in the forearc, before the transition to blueschist assemblages. Fluorine is broadly distributed among phases. The heavy halogen inventory is not controlled by a dominant phase (i.e., amphibole). Rather, these elements are distributed at low concentrations among many phases or are predominantly hosted in non-lattice sites.