Showing papers on "Methane published in 2012"

The GERG-2008 Wide-Range Equation of State for Natural Gases and Other Mixtures: An Expansion of GERG-2004

Abstract: A new equation of state for the thermodynamic properties of natural gases, similar gases, and other mixtures, the GERG-2008 equation of state, is presented in this work. This equation is an expanded version of the GERG-2004 equation. GERG-2008 is explicit in the Helmholtz free energy as a function of density, temperature, and composition. The equation is based on 21 natural gas components: methane, nitrogen, carbon dioxide, ethane, propane, n-butane, isobutane, n-pentane, isopentane, n-hexane, n-heptane, n-octane, n-nonane, n-decane, hydrogen, oxygen, carbon monoxide, water, hydrogen sulfide, helium, and argon. Over the entire composition range, GERG-2008 covers the gas phase, liquid phase, supercritical region, and vapor–liquid equilibrium states for mixtures of these components. The normal range of validity of GERG-2008 includes temperatures from (90 to 450) K and pressures up to 35 MPa where the most accurate experimental data of the thermal and caloric properties are represented to within their accura...

Exceptional Activity for Methane Combustion over Modular Pd@CeO2 Subunits on Functionalized Al2O3

Abstract: There is a critical need for improved methane-oxidation catalysts to both reduce emissions of methane, a greenhouse gas, and improve the performance of gas turbines. However, materials that are currently available either have low activity below 400°C or are unstable at higher temperatures. Here, we describe a supramolecular approach in which single units composed of a palladium (Pd) core and a ceria (CeO(2)) shell are preorganized in solution and then homogeneously deposited onto a modified hydrophobic alumina. Electron microscopy and other structural methods revealed that the Pd cores remained isolated even after heating the catalyst to 850°C. Enhanced metal-support interactions led to exceptionally high methane oxidation, with complete conversion below 400°C and outstanding thermal stability under demanding conditions.

Greater focus needed on methane leakage from natural gas infrastructure

Abstract: Natural gas is seen by many as the future of American energy: a fuel that can provide energy independence and reduce greenhouse gas emissions in the process. However, there has also been confusion about the climate implications of increased use of natural gas for electric power and transportation. We propose and illustrate the use of technology warming potentials as a robust and transparent way to compare the cumulative radiative forcing created by alternative technologies fueled by natural gas and oil or coal by using the best available estimates of greenhouse gas emissions from each fuel cycle (i.e., production, transportation and use). We find that a shift to compressed natural gas vehicles from gasoline or diesel vehicles leads to greater radiative forcing of the climate for 80 or 280 yr, respectively, before beginning to produce benefits. Compressed natural gas vehicles could produce climate benefits on all time frames if the well-to-wheels CH4 leakage were capped at a level 45–70% below current estimates. By contrast, using natural gas instead of coal for electric power plants can reduce radiative forcing immediately, and reducing CH4 losses from the production and transportation of natural gas would produce even greater benefits. There is a need for the natural gas industry and science community to help obtain better emissions data and for increased efforts to reduce methane leakage in order to minimize the climate footprint of natural gas.

Direct Catalytic Conversion of Methane to Methanol in an Aqueous Medium by using Copper‐Promoted Fe‐ZSM‐5

Abstract: Iron copper zeolite (Fe-Cu-ZSM-5) with aqueous hydrogen peroxide is active for the selective oxidation of methane to methanol. Iron is involved in the activation of the carbon–hydrogen bond, while copper allows methanol to form as the major product. The catalyst is stable, re-usable and activates methane giving >90 % methanol selectivity and 10 % conversion in a closed catalytic cycle (see scheme).

Plasma-catalytic dry reforming of methane in an atmospheric dielectric barrier discharge: Understanding the synergistic effect at low temperature

Abstract: A coaxial dielectric barrier discharge (DBD) reactor has been developed for plasma-catalytic dry reforming of CH 4 into syngas over different Ni/γ-Al 2 O 3 catalysts. Three different packing methods are introduced into the single-stage plasma-catalysis system to investigate the influence of catalysts packed into the plasma area on the physical properties of the DBD and determine consequent synergistic effects in the plasma-catalytic dry reforming reactions. Compared to the fully packed reactor, which strongly changes the discharge mode due to a significant reduction in the discharge volume, partially packing the Ni/γ-Al 2 O 3 catalyst either in a radial or axial direction into the discharge gap still shows strong filamentary discharge and significantly enhances the physical and chemical interactions between the plasma and catalyst. Optical emission spectra of the discharge demonstrate the presence of reactive species (CO, CH, C 2 , CO 2 + and N 2 + ) in the plasma dry reforming of methane. We also find the presence of the Ni/γ-Al 2 O 3 catalyst in the plasma has a weak effect on the gas temperature of the CH 4 /CO 2 discharge. The synergistic effect resulting from the integration of the plasma and catalyst is clearly observed when the 10 wt% Ni/γ-Al 2 O 3 catalyst in flake form calcined at 300 °C is partially packed in the plasma, showing both the CH 4 conversion (56.4%) and H 2 yield (17.5%) are almost doubled. The synergy of plasma-catalysis also contributes to a significant enhancement in the energy efficiency for greenhouse gas conversion. This synergistic effect from the combination of low temperature plasma and solid catalyst can be attributed to both strong plasma–catalyst interactions and high activity of the Ni/γ-Al 2 O 3 catalyst calcined at a low temperature.

Hydrocarbon emissions characterization in the Colorado Front Range: A pilot study

Abstract: [1] The multispecies analysis of daily air samples collected at the NOAA Boulder Atmospheric Observatory (BAO) in Weld County in northeastern Colorado since 2007 shows highly correlated alkane enhancements caused by a regionally distributed mix of sources in the Denver-Julesburg Basin. To further characterize the emissions of methane and non-methane hydrocarbons (propane, n-butane, i-pentane, n-pentane and benzene) around BAO, a pilot study involving automobile-based surveys was carried out during the summer of 2008. A mix of venting emissions (leaks) of raw natural gas and flashing emissions from condensate storage tanks can explain the alkane ratios we observe in air masses impacted by oil and gas operations in northeastern Colorado. Using the WRAP Phase III inventory of total volatile organic compound (VOC) emissions from oil and gas exploration, production and processing, together with flashing and venting emission speciation profiles provided by State agencies or the oil and gas industry, we derive a range of bottom-up speciated emissions for Weld County in 2008. We use the observed ambient molar ratios and flashing and venting emissions data to calculate top-down scenarios for the amount of natural gas leaked to the atmosphere and the associated methane and non-methane emissions. Our analysis suggests that the emissions of the species we measured are most likely underestimated in current inventories and that the uncertainties attached to these estimates can be as high as a factor of two.

Iron Particle Size Effects for Direct Production of Lower Olefins from Synthesis Gas

Abstract: The Fischer–Tropsch synthesis of lower olefins (FTO) is an alternative process for the production of key chemical building blocks from non-petroleum-based sources such as natural gas, coal, or biomass. The influence of the iron carbide particle size of promoted and unpromoted carbon nanofiber supported catalysts on the conversion of synthesis gas has been investigated at 340–350 °C, H2/CO = 1, and pressures of 1 and 20 bar. The surface-specific activity (apparent TOF) based on the initial activity of unpromoted catalysts at 1 bar increased 6–8-fold when the average iron carbide size decreased from 7 to 2 nm, while methane and lower olefins selectivity were not affected. The same decrease in particle size for catalysts promoted by Na plus S resulted at 20 bar in a 2-fold increase of the apparent TOF based on initial activity which was mainly caused by a higher yield of methane for the smallest particles. Presumably, methane formation takes place at highly active low coordination sites residing at corners a...

A metal-organic framework with optimized open metal sites and pore spaces for high methane storage at room termerature

Abstract: A 3D porous metal-organic framework and method of making are described. In some embodiments, a 3D porous metal-organic framework may be based on a trinodal (3,3,4) net of zyg topology by the self-assembly of the nonlinear hexacarboxylate (BHB) with the paddle-wheel Cu 2 (COO) 4 cluster. Although its porosity and surface area are moderate, the open copper sites and optimal pore spaces enable the pore spaces to be fully utilized for methane storage, resulting in a high methane storage density and high absolute volumetric methane storage at room temperature and 35 bar. By the immobilization of high density open metal sites and the deliberate control of the pore space for their efficient methane storage, this porous MOF functions as an efficient media for methane and natural gas storage.

Designing Catalysts for Functionalization of Unactivated C–H Bonds Based on the CH Activation Reaction

Abstract: In an effort to augment or displace petroleum as a source of liquid fuels and chemicals, researchers are seeking lower cost technologies that convert natural gas (largely methane) to products such as methanol. Current methane to methanol technologies based on highly optimized, indirect, high-temperature chemistry (>800 °C) are prohibitively expensive. A new generation of catalysts is needed to rapidly convert methane and O2 (ideally as air) directly to methanol (or other liquid hydrocarbons) at lower temperatures (∼250 °C) and with high selectivity.Our approach is based on the reaction between CH bonds of hydrocarbons (RH) and transition metal complexes, LnM–X, to generate activated LnM–R intermediates while avoiding the formation of free radicals or carbocations. We have focused on the incorporation of this reaction into catalytic cycles by integrating the activation of the CH bond with the functionalization of LnM–R to generate the desired product and regenerate the LnM–X complex. To avoid free-radical ...

Influence of temperature on biomass pyrolysis in a conical spouted bed reactor

Abstract: Pinewood sawdust flash pyrolysis has been performed in continuous mode in a pilot plant provided with a conical spouted bed reactor, in the 400–600 °C range. The influence of temperature on the pyrolysis yields and product properties has been studied. Product analysis has been carried out on-line by means of chromatographic methods. High liquid yields have been achieved, with the maximum bio-oil yield (75 wt%) at 500 °C. Gas yield is very low at low temperatures and this fraction is mainly composed of carbon dioxide, carbon monoxide and small amounts of methane, hydrogen and C2–C4 hydrocarbons. Bio-oil has been characterized and its major compounds are phenols, specifically guaiacols at low temperatures and catechols at high temperatures. At 600 °C, there is an increase in light compounds due to the cracking reactions, but no aromatic compounds have been detected due to the low residence time of the volatiles in the reactor. The fuel properties of the bio-oil have been measured and the results indicate that it can be a potential substitute to conventional fuels, although its heating value should be improved by subjecting to further treatments. Char can be used as energy source or as active carbon. The char obtained at 600 °C has a high surface area and is suitable for active carbon production.

Biochar and Emissions of Non-CO2 Greenhouse Gases from Soil

Abstract: Climate change caused by an increase in atmospheric concentrations of greenhouse gases (GHGs) is predicted to cause catastrophic impacts on our planet (IPCC, 2006). This provides the impetus to take action to reduce emissions and increase removal of GHGs from the atmosphere.The soil is both a significant source and sink for the greenhouse gases carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O). As the global warming potential of N2O and CH4 is 298 and 25 times greater, respectively, than the equivalent mass of CO2 in the atmosphere (Forster et al, 2007), small reductions in their emissions could potentially provide significant benefits for the environment.

Anaerobic digestion for global warming control and energy generation—An overview

Abstract: Anaerobic digestion often generates ‘biogas’ – an approximately 3:1 mixture of methane and carbon dioxide – which has been known to be a ‘clean’ fuel since the late 19th century. But a great resurgence of interest in biogas capture – hence methane capture – has occurred in recent years due to the rapidly growing spectre of global warming. Anthropogenic causes which directly or indirectly release methane into the atmosphere, are responsible for as much as a third of the overall additional global warming that is occurring at present. Hence the dual advantage of methane capture – generating energy while controlling global warming – have come to the fore. This paper presents an overview of the natural and the anthropogenic sources that contribute methane to the atmosphere. In this context it underscores the urgency with which the world must develop and enforce methods and practices to enhance methane capture.

The Global Inventory of Methane Hydrate in Marine Sediments: A Theoretical Approach

Abstract: The accumulation of methane hydrate in marine sediments is controlled by a number of physical and biogeochemical parameters including the thickness of the gas hydrate stability zone (GHSZ), the solubility of methane in pore fluids, the accumulation of particulate organic carbon at the seafloor, the kinetics of microbial organic matter degradation and methane generation in marine sediments, sediment compaction and the ascent of deep-seated pore fluids and methane gas into the GHSZ. Our present knowledge on these controlling factors is discussed and new estimates of global sediment and methane fluxes are provided applying a transport-reaction model at global scale. The modeling and the data evaluation yield improved and better constrained estimates of the global pore volume within the modern GHSZ ( ≥ 44 × 1015 m3), the Holocene POC accumulation rate at the seabed (~1.4 × 1014 g yr−1), the global rate of microbial methane production in the deep biosphere (4−25 × 1012 g C yr−1) and the inventory of methane hydrates in marine sediments ( ≥ 455 Gt of methane-bound carbon).

Simultaneous hydrogen utilization and in situ biogas upgrading in an anaerobic reactor

Abstract: The possibility of converting hydrogen to methane and simultaneous upgrading of biogas was investigated in both batch tests and fully mixed biogas reactor, simultaneously fed with manure and hydrogen. Batch experiments showed that hydrogen could be converted to methane by hydrogenotrophic methanogenesis with conversion of more than 90% of the consumed hydrogen to methane. The hydrogen consumption rates were affected by both P(H₂) (hydrogen partial pressure) and mixing intensity. Inhibition of propionate and butyrate degradation by hydrogen (1 atm) was only observed under high mixing intensity (shaking speed 300 rpm). Continuous addition of hydrogen (flow rate of 28.6 mL/(L/h)) to an anaerobic reactor fed with manure, showed that more than 80% of the hydrogen was utilized. The propionate and butyrate level in the reactor was not significantly affected by the hydrogen addition. The methane production rate of the reactor with H₂ addition was 22% higher, compared to the control reactor only fed with manure. The CO₂ content in the produced biogas was only 15%, while it was 38% in the control reactor. However, the addition of hydrogen resulted in increase of pH (from 8.0 to 8.3) due to the consumption of bicarbonate, which subsequently caused slight inhibition of methanogenesis.

A bistable organic-rich atmosphere on the Neoarchaean Earth

Abstract: It has been hypothesized that, before widespread oxygenation about 2.45 billion years ago, the Earth’s atmosphere contained an organic haze similar to that on Titan. However, these theoretical predictions have not been substantiated by geological evidence. Here we use multiproxy geochemical analyses of sediments from the 2.65–2.5-billion-year-old Ghaap Group, in South Africa, to reconstruct ocean and atmospheric chemistry during this time. We find evidence for oxygen production in microbial mats and localized oxygenation of surface waters. Carbon and sulphur isotopes indicate that this oxygen production occurred under a reduced atmosphere that was periodically rich in methane, consistent with the prediction of a hydrocarbon haze. We use a photochemical model to corroborate our geochemical data. Our simulations predict transitions between two stable atmospheric states, one with organic haze and the other haze-free. The transitions are presumably governed by variations in the amount of biological methane production during the Archaean eon. We find that the isotopic signatures we observe are evident in other data sets from this period and conclude that methane was an important component of the atmosphere throughout the Archaean. Before the rise of oxygen, the atmosphere of the early Earth may have consisted of an organic haze. Geochemical data and modelling suggest that from 2.65 to 2.5 Gyr ago, several transitions between hazy and haze-free atmospheric conditions occurred, potentially linked to variations in biogenic methane production.

Homogeneous nucleation of methane hydrates: unrealistic under realistic conditions.

Abstract: Methane hydrates are ice-like inclusion compounds with importance to the oil and natural gas industry, global climate change, and gas transportation and storage. The molecular mechanism by which these compounds form under conditions relevant to industry and nature remains mysterious. To understand the mechanism of methane hydrate nucleation from supersaturated aqueous solutions, we performed simulations at controlled and realistic supersaturation. We found that critical nuclei are extremely large and that homogeneous nucleation rates are extremely low. Our findings suggest that nucleation of methane hydrates under these realistic conditions cannot occur by a homogeneous mechanism.

Carbon dioxide and methane emissions from the Yukon River system

Abstract: [1] Carbon dioxide (CO2) and methane (CH4) emissions are important, but poorly quantified, components of riverine carbon (C) budgets. This is largely because the data needed for gas flux calculations are sparse and are spatially and temporally variable. Additionally, the importance of C gas emissions relative to lateral C exports is not well known because gaseous and aqueous fluxes are not commonly measured on the same rivers. We couple measurements of aqueous CO2 and CH4 partial pressures (pCO2, pCH4) and flux across the water-air interface with gas transfer models to calculate subbasin distributions of gas flux density. We then combine those flux densities with remote and direct observations of stream and river water surface area and ice duration, to calculate C gas emissions from flowing waters throughout the Yukon River basin. CO2 emissions were 7.68 Tg C yr−1 (95% CI: 5.84 −10.46), averaging 750 g C m−2 yr−1 normalized to water surface area, and 9.0 g C m−2 yr−1 normalized to river basin area. River CH4 emissions totaled 55 Gg C yr−1 or 0.7% of the total mass of C emitted as CO2 plus CH4 and ∼6.4% of their combined radiative forcing. When combined with lateral inorganic plus organic C exports to below head of tide, C gas emissions comprised 50% of total C exported by the Yukon River and its tributaries. River CO2 and CH4 derive from multiple sources, including groundwater, surface water runoff, carbonate equilibrium reactions, and benthic and water column microbial processing of organic C. The exact role of each of these processes is not yet quantified in the overall river C budget.

Geologic methane seeps along boundaries of Arctic permafrost thaw and melting glaciers

Abstract: Methane, a potent greenhouse gas, accumulates in subsurface hydrocarbon reservoirs, such as coal beds and natural gas deposits. In the Arctic, permafrost and glaciers form a ‘cryosphere cap’ that traps gas leaking from these reservoirs, restricting flow to the atmosphere. With a carbon store of over 1,200 Pg, the Arctic geologic methane reservoir is large when compared with the global atmospheric methane pool of around 5 Pg. As such, the Earth’s climate is sensitive to the escape of even a small fraction of this methane. Here, we document the release of 14C-depleted methane to the atmosphere from abundant gas seeps concentrated along boundaries of permafrost thaw and receding glaciers in Alaska and Greenland, using aerial and ground surface survey data and in situ measurements of methane isotopes and flux. We mapped over 150,000 seeps, which we identified as bubble-induced open holes in lake ice. These seeps were characterized by anomalously high methane fluxes, and in Alaska by ancient radiocarbon ages and stable isotope values that matched those of coal bed and thermogenic methane accumulations. Younger seeps in Greenland were associated with zones of ice-sheet retreat since the Little Ice Age. Our findings imply that in a warming climate, disintegration of permafrost, glaciers and parts of the polar ice sheets could facilitate the transient expulsion of 14C-depleted methane trapped by the cryosphere cap. In the Arctic, permafrost and glaciers form a ‘cryosphere cap’ that traps methane leaking from hydrocarbon reservoirs, restricting flow to the atmosphere. Aerial surveys and ground-based measurements reveal the release of radiocarbon-depleted methane along boundaries of permafrost thaw and retreating glaciers in Alaska and Greenland.

Selective hydrogen purification through graphdiyne under ambient temperature and pressure.

Abstract: Graphdiyne, a recently synthesized one-atom-thick carbon allotrope, is atomistically porous – characterized by a regular “nanomesh” – and suggests application as a separation membrane for hydrogen purification. Here we report a full atomistic reactive molecular dynamics investigation to determine the selective diffusion properties of hydrogen (H2) amongst carbon monoxide (CO) and methane (CH4), a mixture otherwise known as syngas, a product of the gasification of renewable biomass (such as animal wastes). Under constant temperature simulations, we find the mass flux of hydrogen molecules through a graphdiyne membrane to be on the order of 7 to 10 g cm−2 s−1 (between 300 K and 500 K), with carbon monoxide and methane remaining isolated. Using a simple Arrhenius relation, we determine the energy required for permeation on the order of 0.11 ± 0.03 eV for single H2 molecules. We find that addition of marginal applied force (approximately 1 to 2 pN per molecule, representing a controlled pressure gradient, ΔP, on the order of 100 to 500 kPa) can successfully enhance the separation of hydrogen gas. Addition of larger driving forces (50 to 100 pN per molecule) is required to selectively filter carbon monoxide or methane, suggesting that, under near-atmospheric conditions, only hydrogen gas will pass such a membrane. Graphdiyne provides a unique, chemically inert and mechanically stable platform facilitating selective gas separation at nominal pressures using a homogeneous material system, without a need for chemical functionalization or the explicit introduction of molecular pores.

Potential methane reservoirs beneath Antarctica

Abstract: On the basis of data from other subglacial environments and simulations of the accumulation of methane hydrate in Antarctic sedimentary basins, it seems there could be unsuspected, large stores of methane beneath the Antarctic Ice Sheet. The ice-covered parts of Antarctica are known to be a reservoir of metabolically active microbial cells and organic carbon, but the potential for microorganisms to support the degradation of organic carbon to methane beneath the ice has not yet been evaluated. In this paper, Jemma Wadham and colleagues numerically simulate the accumulation of methane in Antarctic sedimentary basins. Their findings suggest that the Antarctic Ice Sheet may be a neglected but important component of the global methane inventory that could act as a positive feedback on global climate change during episodes of ice-sheet collapse. Once thought to be devoid of life, the ice-covered parts of Antarctica are now known to be a reservoir of metabolically active microbial cells and organic carbon1. The potential for methanogenic archaea to support the degradation of organic carbon to methane beneath the ice, however, has not yet been evaluated. Large sedimentary basins containing marine sequences up to 14 kilometres thick2 and an estimated 21,000 petagrams (1 Pg equals 1015 g) of organic carbon are buried beneath the Antarctic Ice Sheet. No data exist for rates of methanogenesis in sub-Antarctic marine sediments. Here we present experimental data from other subglacial environments that demonstrate the potential for overridden organic matter beneath glacial systems to produce methane. We also numerically simulate the accumulation of methane in Antarctic sedimentary basins using an established one-dimensional hydrate model3 and show that pressure/temperature conditions favour methane hydrate formation down to sediment depths of about 300 metres in West Antarctica and 700 metres in East Antarctica. Our results demonstrate the potential for methane hydrate accumulation in Antarctic sedimentary basins, where the total inventory depends on rates of organic carbon degradation and conditions at the ice-sheet bed. We calculate that the sub-Antarctic hydrate inventory could be of the same order of magnitude as that of recent estimates made for Arctic permafrost. Our findings suggest that the Antarctic Ice Sheet may be a neglected but important component of the global methane budget, with the potential to act as a positive feedback on climate warming during ice-sheet wastage.

Long-term decline of global atmospheric ethane concentrations and implications for methane

Abstract: The longest continuous record of global atmospheric ethane levels is presented, showing that global ethane emission rates decreased by 21 per cent from 1984 to 2010, probably owing to decreased venting and flaring of natural gas in oil fields; decreased venting and flaring also account for at least 30 to 70 per cent of the decrease in methane emissions over the same period. Ethane is the most abundant non-methane hydrocarbon in the remote atmosphere and is a precursor to tropospheric ozone. This paper presents the longest continuous record of global atmospheric ethane levels assembled so far and finds that global ethane-emission rates decreased by 21% between 1984 and 2010. This can probably be attributed to a decrease in fugitive emissions, such as the venting and flaring of natural gas from oil fields, rather than a decline in its other major sources, biofuel use and biomass burning. Because methane shares ethane's main sources of emissions, this new long-term ethane record can be used to investigate changes in global methane levels. This leads the authors to suggest that reduced fugitive fossil-fuel emissions also account for 30–70% of the decrease in global methane emissions. After methane, ethane is the most abundant hydrocarbon in the remote atmosphere. It is a precursor to tropospheric ozone and it influences the atmosphere’s oxidative capacity through its reaction with the hydroxyl radical, ethane’s primary atmospheric sink1,2,3. Here we present the longest continuous record of global atmospheric ethane levels. We show that global ethane emission rates decreased from 14.3 to 11.3 teragrams per year, or by 21 per cent, from 1984 to 2010. We attribute this to decreasing fugitive emissions from ethane’s fossil fuel source—most probably decreased venting and flaring of natural gas in oil fields—rather than a decline in its other major sources, biofuel use and biomass burning. Ethane’s major emission sources are shared with methane, and recent studies have disagreed on whether reduced fossil fuel or microbial emissions have caused methane’s atmospheric growth rate to slow4,5. Our findings suggest that reduced fugitive fossil fuel emissions account for at least 10–21 teragrams per year (30–70 per cent) of the decrease in methane’s global emissions, significantly contributing to methane’s slowing atmospheric growth rate since the mid-1980s.

Ocean-atmosphere trace gas exchange

Abstract: The oceans contribute significantly to the global emissions of a number of atmospherically important volatile gases, notably those containing sulfur, nitrogen and halogens. Such gases play critical roles not only in global biogeochemical cycling but also in a wide range of atmospheric processes including marine aerosol formation and modification, tropospheric ozone formation and destruction, photooxidant cycling and stratospheric ozone loss. A number of marine emissions are greenhouse gases, others influence the Earth's radiative budget indirectly through aerosol formation and/or by modifying oxidant levels and thus changing the atmospheric lifetime of gases such as methane. In this article we review current literature concerning the physical, chemical and biological controls on the sea-air emissions of a wide range of gases including dimethyl sulphide (DMS), halocarbons, nitrogen-containing gases including ammonia (NH3), amines (including dimethylamine, DMA, and diethylamine, DEA), alkyl nitrates (RONO2) and nitrous oxide (N2O), non-methane hydrocarbons (NMHC) including isoprene and oxygenated (O)VOCs, methane (CH4) and carbon monoxide (CO). Where possible we review the current global emission budgets of these gases as well as known mechanisms for their formation and loss in the surface ocean.