The global distribution of methane in the troposphere

Abstract

Methane has been measured in air samples collected at approximately weekly intervals at 23 globally distributed sites in the NOAA/GMCC cooperative flask sampling network. Sites range in latitude from 90" S to 76" N, and at most of these we report 2 years of data beginning in early 1983. All measurements have been made by gas chromatography with a flame ionization detector at the NOAA/GMCC laboratory in Boulder, Colorado. All air samples have been referenced to a single secondary standard of methane-in-air, ensuring a high degree of internal consistency in the data. The precision of measurements is estimated from replicate determinations on each sample as 0.2%. The latitudinal distribution of methane and the seasonal variation of this distribution in the marine boundary layer has been defined in great detail, including a remarkable uniformity in background levels of methane in the Southern Hemisphere. We report for the first time the observation of a complete seasonal cycle of methane at the South Pole. A significant vertical gradient is observed between a sea level and a high altitude site in Hawaii. Globally averaged background concentrations in the marine boundary layer have been calculated for the 2 year-period May 1983-April 1985 inclusive, from which we find an average increase of 12.8 ppb per year, or 0.78% per year when referenced to the globally averaged concentration (1625 ppb) at the mid-point of this period. We present evidence that there has been a slowing down in the methane growth rate.

Methane bubbling from northern lakes: present and future contributions to the global methane budget

“…In northern high latitudes, where the concentration of atmospheric CH 4 is highest and where much of atmospheric CH 4 originates (Steele et al 1987;Fung et al 1991), lakes are a dominant landscape feature occupying as much as 48% of the land surface in some regions (Riordan et al 2006). Lakes are important emitters of CH 4 , particularly when attention is paid to ebullition (Hamilton et al 1994;Keller & Stallard 1994;Zimov et al 1997;Walter et al 2006).…”

Atmospheric Trends in Methylchloroform and the Global Average for the Hydroxyl Radical

“…(22). The major tropospheric sink for methane is reaction with the hydroxyl radical with a rate constant similar to that for methylchioroform (23).…”

Continuous Monitoring of the Methane Concentration in the Urban Atmosphere of Nagoya, 1990–1993

“…In the northern hemisphere, the atmospheric CH4 concentration is usually higher than that in the southern hemisphere.20 It is also known that the atmospheric CH4 concentration is higher in the northern parts of the northern hemisphere. 20 In comparison with the atmospheric CH4 concentrations during 1992 at almost the same latitude, for example, it was less than 1.8 ppmv in Cold Bay, Alaska (55° 12'N) and less than 1.7 ppmv in Mauna Loa, Hawaii (19° 32'N). In spite of such a ununiform distribution of methane, the annual mean value of the atmospheric CH4 concentration in Nagoya (35° 10'N), which was 1.93 ppmv in 1992, was apparently much higher compared with those in the global atmosphere.…”

“…It should, however, be stressed here that the annual mean values during the last 3 years, from 1991 to 1993, were significantly larger in Nagoya than the global mean value13, or the mean values in the northern hemisphere. 20 In fact, the atmospheric CH4 concentration is not uniformly distributed all over the world. In the northern hemisphere, the atmospheric CH4 concentration is usually higher than that in the southern hemisphere.20 It is also known that the atmospheric CH4 concentration is higher in the northern parts of the northern hemisphere.…”