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.

Isotopic composition of formaldehyde in urban air.

The isotopic composition of atmospheric formaldehyde was measured in air samples collected in urban Seattle, Washington. A recently developed gas chromatography-isotope ratio mass spectrometry analytical technique was used to extract formaldehyde directly from whole air, separate it from other volatile organic compounds, and measure its (13)C/(12)C and D/H ratio. Measurements of formaldehyde concentration were also made concomitant with isotope ratio.

Isotopic analysis of atmospheric formaldehyde by gas chromatography isotope ratio mass spectrometry.

Little is known about the isotopic composition of formaldehyde in the atmosphere, a chemical intermediate in hydrocarbon oxidation. Here, we present a promising new method to analyze the carbon (delta 13C) and hydrogen (delta D) isotopic composition of atmospheric formaldehyde. The direct isotopic analytical technique described uses continuous-flow gas chromatography-isotope ratio mass spectrometry, which provides flexibility for either isotopic analysis without correction for derivative functional groups.