Atmospheric methane removal is a category of potential approaches being researched to accelerate the breakdown of methane that is in the atmosphere, for the purpose of mitigating some of the impacts of climate change. [1]
Atmospheric methane has increased since pre-industrial times from 0.7 ppm to 1.9 ppm. [2] From 2010 to 2019, methane emissions caused 0.5 °C (about 30%) of observed global warming. [3] [4] Global methane emissions approached a record 600 Tg CH4 per year in 2017. [1]
Methane has a limited atmospheric lifetime, about 10 years, due to substantial methane sinks. The primary methane sink is atmospheric oxidation, from hydroxyl radicals (~90% of the total sink) and chlorine radicals (0-5% of the total sink). The rest is consumed by methanotrophs and other methane-oxidizing bacteria and archaea in soils (~5%). [5]
Different methods to remove methane from the atmosphere include thermal-catalytic oxidation, photocatalytic oxidation, biological methanotrophic methane removal, concentration with zeolites or other porous solids, and separation by membranes. [6]
Potential methods can be categorized by the underlying catalytic process, or the potential deployment form.
Enhanced Atmospheric Methane Oxidation is the concept of enhancing the overall oxidative methane sink in the atmosphere, through generating additional hydroxyl or chlorine atmospheric radicals.
Iron salt aerosols are one proposed method of enhanced atmospheric methane oxidation which involves lofting iron-based particles into the atmosphere (e.g. from planes [7] or ships) to enhance atmospheric chlorine radicals, a natural methane sink. [8] Winds over the Sahara raise dust into the troposphere and disperse it over the Atlantic. [9] A 2023 study suggests that this has contributed to natural atmospheric methane oxidation. [10] [11]
Iron salt aerosols are being studied for the potential of iron(III) chloride (FeCl3) to catalyze chlorine radical production. [12] Chlorine atoms are produced by photolysis from the FeCl3 stemming from iron-containing airborne dust aerosol particles in the oceanic boundary layer. [13]
The chlorine atoms initiate methane oxidation:
The resulting methyl radical is unstable and oxidises naturally to CO2 and water:
Fine particles dispersed in the atmosphere can serve as cloud condensation nuclei and thereby cause marine cloud brightening [14]
Eventually all FeCl3 particles are washed out of the air and fall on land or water, where they dissolve into iron compounds and salt. [12]
Iron salt aerosols may also therefore contribute to iron fertilization.
Soil bacteria and archaea account for approximately 5% of the natural methane sink. Early research is going into how the activity of these bacteria may be able to be enhanced, either through the use of soil amendments, or introduction of selected or engineered methane-oxidizing bacteria. [15]
Catalytic engineered systems are designed to pass air from the atmosphere, either passively or actively, through catalytic systems which leverage energy from the sun, an artificial light, or heat to oxidize methane. These catalysts include thermocatalysts, photocatalysts, and radicals produced artificially through photolysis (using light to break apart a molecule). [15]
Sulfur dioxide or sulphur dioxide is the chemical compound with the formula SO
2. It is a toxic gas responsible for the odor of burnt matches. It is released naturally by volcanic activity and is produced as a by-product of copper extraction and the burning of sulfur-bearing fossil fuels. It was known to alchemists as "volatile spirit of sulfur" since at least 16th century.
The sulfate or sulphate ion is a polyatomic anion with the empirical formula SO2−4. Salts, acid derivatives, and peroxides of sulfate are widely used in industry. Sulfates occur widely in everyday life. Sulfates are salts of sulfuric acid and many are prepared from that acid.
Iron(III) chloride describes the inorganic compounds with the formula FeCl3(H2O)x. Also called ferric chloride, these compounds are some of the most important and commonplace compounds of iron. They are available both in anhydrous and in hydrated forms which are both hygroscopic. They feature iron in its +3 oxidation state. The anhydrous derivative is a Lewis acid, while all forms are mild oxidizing agents. It is used as a water cleaner and as an etchant for metals.
Cloud condensation nuclei (CCNs), also known as cloud seeds, are small particles typically 0.2 µm, or one hundredth the size of a cloud droplet. CCNs are a unique subset of aerosols in the atmosphere on which water vapour condenses. This can affect the radiative properties of clouds and the overall atmosphere. Water vapour requires a non-gaseous surface to make the transition to a liquid; this process is called condensation.
The hydroxyl radical, •HO, is the neutral form of the hydroxide ion (HO–). Hydroxyl radicals are highly reactive and consequently short-lived; however, they form an important part of radical chemistry. Most notably hydroxyl radicals are produced from the decomposition of hydroperoxides (ROOH) or, in atmospheric chemistry, by the reaction of excited atomic oxygen with water. It is also an important radical formed in radiation chemistry, since it leads to the formation of hydrogen peroxide and oxygen, which can enhance corrosion and SCC in coolant systems subjected to radioactive environments. Hydroxyl radicals are also produced during UV-light dissociation of H2O2 (suggested in 1879) and likely in Fenton chemistry, where trace amounts of reduced transition metals catalyze peroxide-mediated oxidations of organic compounds.
The pedosphere is the outermost layer of the Earth that is composed of soil and subject to soil formation processes. It exists at the interface of the lithosphere, atmosphere, hydrosphere and biosphere. The pedosphere is the skin of the Earth and only develops when there is a dynamic interaction between the atmosphere, biosphere, lithosphere and the hydrosphere. The pedosphere is the foundation of terrestrial life on Earth.
Trace gases are gases that are present in small amounts within an environment such as a planet's atmosphere. Trace gases in Earth's atmosphere are gases other than nitrogen (78.1%), oxygen (20.9%), and argon (0.934%) which, in combination, make up 99.934% of its atmosphere.
The iron cycle (Fe) is the biogeochemical cycle of iron through the atmosphere, hydrosphere, biosphere and lithosphere. While Fe is highly abundant in the Earth's crust, it is less common in oxygenated surface waters. Iron is a key micronutrient in primary productivity, and a limiting nutrient in the Southern ocean, eastern equatorial Pacific, and the subarctic Pacific referred to as High-Nutrient, Low-Chlorophyll (HNLC) regions of the ocean.
The hydrogen cycle consists of hydrogen exchanges between biotic (living) and abiotic (non-living) sources and sinks of hydrogen-containing compounds.
In atmospheric chemistry, NOx is shorthand for nitric oxide and nitrogen dioxide, the nitrogen oxides that are most relevant for air pollution. These gases contribute to the formation of smog and acid rain, as well as affecting tropospheric ozone.
The Great Oxidation Event (GOE) or Great Oxygenation Event, also called the Oxygen Catastrophe, Oxygen Revolution, Oxygen Crisis or Oxygen Holocaust, was a time interval during the Early Earth's Paleoproterozoic era when the Earth's atmosphere and the shallow ocean first experienced a rise in the concentration of oxygen. This began approximately 2.460–2.426 Ga (billion years) ago during the Siderian period and ended approximately 2.060 Ga ago during the Rhyacian. Geological, isotopic, and chemical evidence suggests that biologically produced molecular oxygen (dioxygen or O2) started to accumulate in Earth's atmosphere and changed it from a weakly reducing atmosphere practically devoid of oxygen into an oxidizing one containing abundant free oxygen, with oxygen levels being as high as 10% of their present atmospheric level by the end of the GOE.
Iron fertilization is the intentional introduction of iron-containing compounds to iron-poor areas of the ocean surface to stimulate phytoplankton production. This is intended to enhance biological productivity and/or accelerate carbon dioxide sequestration from the atmosphere. Iron is a trace element necessary for photosynthesis in plants. It is highly insoluble in sea water and in a variety of locations is the limiting nutrient for phytoplankton growth. Large algal blooms can be created by supplying iron to iron-deficient ocean waters. These blooms can nourish other organisms.
Tropospheric ozone depletion events are phenomena that reduce the concentration of ozone in the earth's troposphere. Ozone (O3) is a trace gas which has been of concern because of its unique dual role in different layers of the lower atmosphere. Apart from absorbing UV-B radiation and converting solar energy into heat in the stratosphere, ozone in the troposphere provides greenhouse effect and controls the oxidation capacity of the atmosphere.
The surface color of the planet Mars appears reddish from a distance because of rusty atmospheric dust. From close up, it looks more of a butterscotch, and other common surface colors include golden, brown, tan, and greenish, depending on minerals.
Stratospheric aerosol injection is a proposed method of solar geoengineering to reduce global warming. This would introduce aerosols into the stratosphere to create a cooling effect via global dimming and increased albedo, which occurs naturally from volcanic winter. It appears that stratospheric aerosol injection, at a moderate intensity, could counter most changes to temperature and precipitation, take effect rapidly, have low direct implementation costs, and be reversible in its direct climatic effects. The Intergovernmental Panel on Climate Change concludes that it "is the most-researched [solar geoengineering] methodagreement that it could limit warming to below 1.5 °C (2.7 °F)." However, like other solar geoengineering approaches, stratospheric aerosol injection would do so imperfectly and other effects are possible, particularly if used in a suboptimal manner.
Atmospheric methane is the methane present in Earth's atmosphere. The concentration of atmospheric methane is increasing due to methane emissions, and is causing climate change. Methane is one of the most potent greenhouse gases. Methane's radiative forcing (RF) of climate is direct, and it is the second largest contributor to human-caused climate forcing in the historical period. Methane is a major source of water vapour in the stratosphere through oxidation; and water vapour adds about 15% to methane's radiative forcing effect. The global warming potential (GWP) for methane is about 84 in terms of its impact over a 20-year timeframe, and 28 in terms of its impact over a 100-year timeframe.
Greenhouse gas emissions from wetlands of concern consist primarily of methane and nitrous oxide emissions. Wetlands are the largest natural source of atmospheric methane in the world, and are therefore a major area of concern with respect to climate change. Wetlands account for approximately 20–30% of atmospheric methane through emissions from soils and plants, and contribute an approximate average of 161 Tg of methane to the atmosphere per year.
The atmospheric carbon cycle accounts for the exchange of gaseous carbon compounds, primarily carbon dioxide, between Earth's atmosphere, the oceans, and the terrestrial biosphere. It is one of the faster components of the planet's overall carbon cycle, supporting the exchange of more than 200 billion tons of carbon in and out of the atmosphere throughout the course of each year. Atmospheric concentrations of CO2 remain stable over longer timescales only when there exists a balance between these two flows. Methane, Carbon monoxide (CO), and other man-made compounds are present in smaller concentrations and are also part of the atmospheric carbon cycle.
Barbara J. Finlayson-Pitts is a Canadian-American atmospheric chemist. She is a professor in the chemistry department at the University of California, Irvine and is the Director of AirUCI Institute. Finlayson-Pitts and James N. Pitts, Jr. are the authors of Chemistry of the Upper and Lower Atmosphere: Theory, Experiments, and Applications (1999). She has been a member of the National Academy of Sciences since 2006 and is the laureate for the 2017 Garvan–Olin Medal. In 2016 she co-chaired the National Academy of Science report "The Future of Atmospheric Chemistry Research"
Saharan dust is an aeolian mineral dust from the Sahara desert, the largest hot desert in the world. The desert spans just over 9 million square kilometers, from the Atlantic Ocean to the Red Sea, from the Mediterranean sea to the Niger River valley and the Sudan region in the south.