Atmospheric methane

About: Atmospheric methane is a research topic. Over the lifetime, 2034 publications have been published within this topic receiving 119616 citations.

Four-dimensional variational data assimilation for inverse modelling of atmospheric methane emissions: method and comparison with synthesis inversion

Abstract: A four-dimensional variational (4D-Var) data assimilation system for inverse modelling of atmospheric methane emissions is presented. The system is based on the TM5 atmospheric transport model. It can be used for assimilating large volumes of measurements, in particular satellite observations and quasi-continuous in-situ observations, and at the same time it enables the optimization of a large number of model parameters, specifically grid-scale emission rates. Furthermore, the variational method allows to estimate uncertainties in posterior emissions. Here, the system is applied to optimize monthly methane emissions over a 1-year time window on the basis of surface observations from the NOAA-ESRL network. The results are rigorously compared with an analogous inversion by Bergamaschi et al. (2007), which was based on the traditional synthesis approach. The posterior emissions as well as their uncertainties obtained in both inversions show a high degree of consistency. At the same time we illustrate the advantage of 4D-Var in reducing aggregation errors by optimizing emissions at the grid scale of the transport model. The full potential of the assimilation system is exploited in Meirink et al. (2008), who use satellite observations of column-averaged methane mixing ratios to optimize emissions at high spatial resolution, taking advantage of the zooming capability of the TM5 model.

Atmospheric methane : its role in the global environment

Abstract: 1 Atmospheric Methane: An Introduction.- Record of Atmospheric Methane.- 2 The Ice Core Record of Atmospheric Methane.- 3 The Isotopic Composition of Atmospheric Methane and Its Sources.- Formation and Consumption of Methane.- 4 Biological Formation and Consumption of Methane.- Sources and Sinks.- 5 Can Stable Isotopes and Global Budgets Be Used to Constrain Atmospheric Methane Budgets?.- 6 Methane Sinks, Distributions, and Trends.- 7 Sources of Methane: An Overview.- Methane Emissions from Individual Sources.- 8 Ruminants and Other Animals.- 9 Rice Agriculture: Factors Controlling Emissions.- 10 Rice Agriculture: Emissions.- 11 Biomass Burning.- 12 Wetlands.- 13 Waste Management.- 14 Fossil Fuel Industries.- 15 Geological Sources of Methane.- The Environmental Role of Methane and Current Issues.- 16 Methane in the Global Environment.

Role of methane and biogenic volatile organic compound sources in late glacial and Holocene fluctuations of atmospheric methane concentrations

Abstract: Recent analyses of ice core methane concentrations suggested that methane emissions from wetlands were the primary driver for prehistoric changes in atmospheric methane. However, these interpretations conflict as to the location of wetlands, magnitude of emissions, and the environmental controls on methane oxidation. The flux of other reactive trace gases to the atmosphere also controls apparent atmospheric methane concentrations because these compounds compete for the hydroxyl radical (OH), which is the primary atmospheric sink for methane. In a series of linked biosphere-atmosphere chemistry-climate modeling experiments, we simulate the methane and biogenic volatile organic compound emissions from the terrestrial biosphere from the Last Glacial Maximum (LGM) to the present. Using a state-of-the-art chemistry-climate model, we simulate the atmospheric concentrations of methane, OH, and other reactive trace gas species. Over the past 21,000 years, methane emissions from wetlands increased slightly to the end of the Pleistocene but then decreased again, reaching levels at the preindustrial Holocene that were similar to the LGM. Global wetland area decreased by 14% from LGM to the preindustrial time. Emissions of biogenic volatile organic compounds (BVOCs), however, nearly doubled over the same period of time. Atmospheric OH burdens and methane concentrations were affected by this major change in BVOC emissions, with methane lifetimes increasing by more than 2 years from LGM to the present. We simulate a change in methane concentration of ∼385 ppb, accounting for 88% of the ∼440 ppb increase in methane concentrations observed in ice cores. Thus glacial-interglacial changes in atmospheric methane concentrations would have been modulated by BVOC emissions. In addition, the increase in atmospheric methane concentrations since the mid-Holocene is partly caused in our results by the increases in anthropogenic methane emissions over this period. While the interplay between BVOC and wetland methane emissions since the LGM cannot explain the entire record of ice core methane concentrations, consideration of BVOC source dynamics is central to understanding ice core methane. Rapid changes in atmospheric methane concentrations, also observed in ice cores, require further study.

Microbial controls on methane fluxes from a polygonal tundra of the Lena Delta, Siberia

Abstract: Permafrost soils of high-latitude wetlands are an important source of atmospheric methane. In order to improve our understanding of the large seasonal fluctuations of trace gases, we measured the CH4 fluxes as well as the fundamental processes of CH4 production and CH4 oxidation under in situ conditions in a typical polygon tundra in the Lena Delta, Siberia. Net CH4 fluxes were measured from the polygon depression and from the polygon rim from the end of May to the beginning of September 1999. The mean flux rate of the depression was 53.2 ± 8.7 mg CH4 m−2 d−1 with maximum in mid-July (100–120 mg CH4 m−2 d−1), whereas the mean flux rate of the dryer rim part of the polygon was 4.7 ± 2.5 CH4 m−2 d−1. The microbial CH4 production and oxidation showed significant differences during the vegetation period. The CH4 production in the upper soil horizon of the polygon depression was about 10 times higher (38.9 ± 2.9 nmol CH4 h−1 g−1) in July than in August (4.7 ± 1.3 nmol CH4 h−1 g−1). The CH4 oxidation behaved exactly in reverse: the oxidation rate of the upper soil horizon was low (1.9 ± 0.3 nmol CH4 h−1 g−1) in July compared to the activity in August (max. 7.0 ± 1.3 nmol CH4 h−1 g−1). The results indicated clearly an interaction between the microbiological processes with the observed seasonal CH4 fluctuations. However, the CH4 production is primarily substrate dependent, while the oxidation is dependent on the availability of oxygen. The temperature plays only a minor role in both processes, probably because the organisms are adapted to extreme temperature conditions of the permafrost. For the understanding of the carbon dynamics in permafrost soils, a differentiated small-scale view of the microbiological processes and the associated modes of CH4 fluxes is necessary, especially at key locations such as the Siberian Arctic.

Natural marine seepage blowout: Contribution to atmospheric methane

Abstract: The release of methane sequestered within deep-sea methane hydrates is postulated as a mechanism for abrupt climate change; however, whether emitted seabed methane reaches the atmosphere is debatable. We observed methane emissions for a blowout from a shallow (22 m) hydrocarbon seep. The emission from the blowout was determined from atmospheric plume measurements. Simulations suggest a 1.1% gas loss to dissolution compared to ∼ 10% loss for a typical low-flux bubble plume. Transfer to the atmosphere primarily was enhanced by the rapid upwelling flows induced by the massive discharge. This mechanism could allow methane suddenly released from deeper (>250 m) waters to contribute significantly to atmospheric methane budgets. Copyright 2006 by the American Geophysical Union.