Suggested Citation:"Glossary." National Academies of Sciences, Engineering, and Medicine. 2019. Negative Emissions Technologies and Reliable Sequestration: A Research Agenda. Washington, DC: The National Academies Press. doi: 10.17226/25259.
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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. |
| Calciner | A kiln where calcium carbonate is heated with natural gas to produce solid calcium oxide in a direct air capture liquid solvent system. |
| Capillary or residual gas trapping | Immobilization of CO2 as a result of interaction with pore space in a geologic storage reservoir. |
| Carbon dioxide removal | Intentional efforts to remove carbon dioxide from the atmosphere. Such efforts 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. |
| Causticizer | A reactor where calcium carbonate is precipitated in a liquid solvent direct air capture system. |
| CO2e | A unit of measure of the amount of CO2 that would have an equivalent global warming impact as a greenhouse gas of interest. |
Suggested Citation:"Glossary." National Academies of Sciences, Engineering, and Medicine. 2019. Negative Emissions Technologies and Reliable Sequestration: A Research Agenda. Washington, DC: The National Academies Press. doi: 10.17226/25259.
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| 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 liquefaction | A thermochemical process where biomass is converted to produce predominantly liquids via heating in water, where the water acts as a reactant. |
| Integrated assessment modeling | A quantitative tool for combining diverse fields (i.e., science, economics, and policy) to assess an impact, in this case the impact of emissions or emissions reductions. |
| Levelized cost of energy | The net present value of energy production over the lifetime of the generating source. |
| Life cycle analysis or life cycle assessment | An assessment of all of the environmental impacts over the lifetime of a 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. |
Suggested Citation:"Glossary." National Academies of Sciences, Engineering, and Medicine. 2019. Negative Emissions Technologies and Reliable Sequestration: A Research Agenda. Washington, DC: The National Academies Press. doi: 10.17226/25259.
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| Mantle | Relatively dense, ultramafic layer of the solid Earth, underlying the crust. The upper mantle—from the base of the crust to ~410 km depth—is composed of peridotite and contains abundant Mg-rich olivine. |
| Negative emissions technology | An approach that removes CO2 from the atmosphere to be sequestered. |
| Olivine | Mineral solid solution between endmembers forsterite (Mg-2SiO4) and fayalite (Fe2SiO4). Olivine comprises more than 60% of Earth’s upper mantle, where it is > 88% forsterite. |
| Ophiolite | Block of oceanic crust and upper mantle, an oceanic plate, thrust onto a continental margin. |
| Peridotite | Ultramafic rock containing greater than 40% olivine (aka the gemstone “peridot”). Peridotite comprises most of Earth’s 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 peridotites. Rocks with |
Suggested Citation:"Glossary." National Academies of Sciences, Engineering, and Medicine. 2019. Negative Emissions Technologies and Reliable Sequestration: A Research Agenda. Washington, DC: The National Academies Press. doi: 10.17226/25259.
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| greater 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. |
| 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. |
| Solubility trapping | Secondary trapping mechanism for geologic storage resulting from dissolution of CO2 into an aquifer. |
| 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% “mafic minerals,” which are olivine, pyroxenes, amphiboles, and serpentines. Ultramafic |
Suggested Citation:"Glossary." National Academies of Sciences, Engineering, and Medicine. 2019. Negative Emissions Technologies and Reliable Sequestration: A Research Agenda. Washington, DC: The National Academies Press. doi: 10.17226/25259.
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| rocks including peridotite comprise most of Earth’s 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. |
