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Glossary Afforestation Planting forest on lands that were originally grasslands or shrublands. Avoided emissions Greenhouse gas emissions reductions resulting from the avoidance or reduction of an emitting activity (e.g., preventing deforestation). Biochar A solid carbon product of biomass thermochemical conversion. Brucite Magnesium hydroxide mineral, Mg(OH)2, commonly formed together with serpentine during hydration of ultramafic rocks. Capillary or residual Immobilization of CO2 as a result of interaction with pore space in a gas trapping geologic storage reservoir. Carbon dioxide Intentional efforts to remove carbon dioxide from the atmosphere. NETs removal complement carbon capture and sequestration methods that primarily focus on reducing CO2 emissions from point sources such as fossil fuel power plants. Carbonates minerals such as magnesite (MgCO3), calcite (CaCO3) and dolomite (MgCa(CO3)2). Formation of carbonate minerals by reaction of CO2 with Mg- and Ca-bearing silicates is commonly called carbonation and carbon mineralization. Calciner A kiln where calcium carbonate is heated with natural gas to produce solid calcium oxide in a direct air capture liquid solvent system. Causticizer A reactor where calcium carbonate is precipitated in a liquid solvent direct air capture system. CO2 equivalent A unit of measure of the amount of CO2 that would have an equivalent global warming impact as a greenhouse gas of interest. Combustion The most oxidizer-enriched of the thermochemical conversion paths, where sufficient oxidizer such as air or oxygen is provided to ensure complete oxidation of biomass for the production of power and/or heat. Crust Relatively low density, SiO2-rich, uppermost layer of the solid Earth; oceanic crust is mafic, and about 7 km thick; continental crust is intermediate to felsic, with more Si, Al, Na, K than oceanic crust, and a variable thickness averaging ~ 36 km. Exergy The capacity of energy to do physical work. Gasification A process where a gasifying agent such as steam, air, or CO2 is used to partially oxidize biomass and produce high yields of combustible gases. Hydrothermal A thermochemical process where biomass is converted to produce liquefaction predominantly liquids via heating in water, where the water acts as a reactant. Integrated assessment A quantitative tool for combining diverse fields (i.e., science, economics, modeling and policy) to assess an impact, in this case the impact of emissions or emissions reductions. PREPUBLICATION COPY 277
278 Negative Emissions Technologies and Reliable Sequestration: A Research Agenda Levelized cost The net present value of energy production over the lifetime of the of energy generating source. Life cycle analysis An assessment of all of the environmental impacts over the lifetime of a or life cycle assessment product, from raw material to consumption. Listvenite rock composed of carbonate minerals + quartz + Fe-oxides + Cr-rich oxides or silicates, produced by complete carbonation of peridotite, in which all Mg and Ca combine with CO2 to form carbonate minerals, most Fe forms oxides, and all SiO2 forms quartz. Mafic rock containing ~ 45-53 wt% SiO2, and/or composed of > 10 wt% Ca-rich plagioclase (> 50% An), typically with olivine, pyroxenes and amphiboles, and no quartz. Mafic lavas are basalts. Mafic plutonic rocks are gabbros (sensu lato). Some mafic intrusions host significant ore deposits ((Ni, Cr, platinum group elements). Gabbroic rocks with very abundant plagioclase are called anorthosites. Mantle Relatively dense, ultramafic layer of the solid Earth, underlying the crust. The upper mantleâfrom the base of the crust to ~ 410 km depthâis composed of peridotite and contains abundant Mg-rich olivine. Negative emissions An approach that removes CO2 from the atmosphere to be sequestered. technology Olivine mineral solid solution between end-members forsterite (Mg2SiO4) and fayalite (Fe2SiO4). Olivine comprises more than 60% of the Earthâs upper mantle, where it is > 88% forsterite. Ophiolite block of oceanic crust and upper mantleâan oceanic plateâthrust onto a continental margin. Peridotite ultramafic rock containing more than 40% olivine (aka the gemstone âperidotâ). Peridotite comprises most of the Earthâs upper mantle. Plagioclase A solid solution mineral, part of the feldspar group, with compositions ranging continuously from anorthite (An, CaAl2Si2O8) to albite (Ab, NaAlSi3O8), including bytownite (Byt, 70-90% An), labradorite (Lab, 50- 70% An), andesine (30-50% An) and oligoclase (10-30% An). Plagioclase, particularly labradorite, is a common constituent of crystalline basalt (mantle-derived lava) and its slowly cooled, plutonic equivalent gabbro, together with ~ 0-20% olivine and 0-40% pyroxenes. Progradation Sediment deposition in wetlands that results in lateral of growth of the seaward edge. Pyrolysis a highly oxidizer deficient or anoxic thermochemical process in which biomass is heated in the absence of air to produce liquids and gases, which may be upgraded to biofuels or directly combusted, and solid carbon-rich biochar, which may be combusted, gasified or distributed in soil for storage and soil amendment. Pyroxene Fe-Mg silicates including orthopyroxene, with Mg-endmember enstatite (En, Mg2Si2O6), and calcium-rich pyroxene with Mg-endmember diopside (Di, CaMgSi2O6). Mg-rich pyroxenes comprise 0-40% of mantle PREPUBLICATION COPY
Glossary 279 peridotites. Rocks with more than 60% pyroxene with less than 10% feldspar are pyroxenites. Quartz SiO2 mineral. Reforestation Planting forest on lands that used to be forest, but were converted to another use. Serpentine hydrous silicate minerals with Mg-endmembers Mg3Si2O5(OH)4. Formation of serpentine plus other minerals by hydration of ultramafic rocks is often called serpentinization. Rocks composed mainly of serpentine are called serpentinites. Polytypes of serpentine include chrysotile, lizardite and antigorite. Chrysotile and lizardite are common products of low temperature hydration of ultramafic rocks and of olivine and pyroxene in mafic rocks. Solubility trapping Secondary trapping mechanism for geologic storage resulting from dissolution of CO2 into an aquifer. Slaker A reactor where calcium oxide reacts with water to regenerate calcium oxide for reuse in a causticizer as part of a liquid solvent direct air capture system. Solid sorbent The capture surface for direct air capture systems utilizing adsoption and desorption to a CO2-sorbent material. Spreading ridge narrow zone of extension and formation of new, igneous oceanic crust from basaltic partial melts of the upper mantle rising between two diverging tectonic plates. Subduction zone thrust fault at zone of convergence between two tectonic plates where one plate is thrust beneath the other; typically, old oceanic crust is thrust into the mantle. Supercritical CO2 CO2 gas compressed to a fluid above its critical temperature and pressure. Transgression (of wetlands) Migration of a tidal wetland into adjacent uplands as sea levels rise. Ultramafic rock containing < 45 wt% SiO2 and > 18 wt% MgO, and/or composed of > 90 wt% âmafic mineralsâ, which are olivine, pyroxenes, amphiboles and serpentines. Ultramafic rocks including peridotite comprise most of the Earthâs upper mantle to a depth of about 410 km below the surface, and also form igneous rocks that host significant ore deposits, including explosively emplaced kimberlites (diamonds), igneous intrusions including peridotites and pyroxenites (Ni, Cr, platinum group elements) and ultramafic lavas known as komatiites (Ni). Wollastonite Ca-silicate mineral CaSiO3 most commonly found where granitic intrusions reacted with limestones. PREPUBLICATION COPY