Atmospheric methane isotopic record favors fossil sources flat in 1980s and 1990s with recent increase.

Observations of atmospheric methane (CH4) since the late 1970s and measurements of CH4 trapped in ice and snow reveal a meteoric rise in concentration during much of the twentieth century. Since 1750, levels of atmospheric CH4 have more than doubled to current globally averaged concentration near 1,800 ppb. During the late 1980s and 1990s, the CH4 growth rate slowed substantially and was near or at zero between 1999 and 2006.

Atmospheric methane: trends and cycles of sources and sinks.

For more than 20 years the global emissions and the lifetime of methane have probably been constant, so the buildup of methane in the atmosphere has been slowing down for as long. During this time, there have been periodic events occurring every seven to eight years, when global methane concentrations increased by some 10 ppb and later fell back, in some cases due to temporary increases of emissions from the northern tropics that spread to the global scale. These conclusions are derived from the accumulated global observations that now span 23 years and define the role of human activities in the recent cycle of atmospheric methane.

Changes in the regional emissions of greenhouse gases and ozone-depleting compounds.

In the wake of the Kyoto and Montreal Protocols, there is a need to verify whether policies to reduce emissions are working. We present data showing that emissions of ozone-depleting compounds, such as the chlorofluorocarbons and methyl chloroform, are decreasing from some regions of the United States but emissions of the greenhouse gases do not appear to be declining.

Atmospheric perfluorocarbons.

Collectively, man-made emissions of a few greenhouse gases may cause about the same amount of global warming as increasing carbon dioxide. Among the most potent of these non-CO2 greenhouse gases are the perfluorocarbons that have extraordinarily long atmospheric lifetimes of 10,000 to more than 50,000 yr. We report atmospheric concentrations over two decades, between 1978 and 1997, of the three most abundant perfluorocarbons--CF4, C2F6, and C3F8--and delineate the sources that account for the present abundances and trends.

Biogenic Fraction of Ambient VOC: Comparison of Radiocarbon, Chromatographic, and Emissions Inventory Estimates for Atlanta, Georgia.

Previously reported volatile organic compounds (VOC) radiocarbon (C) measurements for 1992 summertime Atlanta, GA, have been compared with chromatographic data and emissions inventory predictions. The chromatographic approach that was used provided a more comprehensive VOC characterization than typically achieved, and the emissions inventory was research-grade level (date-, site-, and time-specific). The comparisons are in general agreement that biogenic emissions contribute only modestly (<10%) to the VOC content of the particular ambient samples that were collected and measured.