The first two are important greenhouse gases that are increasing due to man's activities. CH 4 and CO influence the oxidizing capacity of the earth's atmosphere through their reactivity with HO radicals. The goal of the research is to elucidate the sources, sinks, and pathways of these compounds, so that, ultimately, our society will have the option of rational control, based on scientific undertstanding, of atmospheric greenhouse gas levels and climate forcing. A major tool is a network of observations, through the analysis of whole air samples obtained throughout the world, and through the continuous operation of instruments on tall towers, ships, and in remote atmospheric observatories. The analytical methods are infrared absorption, gas chromatography, and mass spectrometry.
High accuracy is a fundamental requirement for all measurements.
Quantitative information about sources and sinks on large spatial scales is extracted from small but persistent concentration differences. Major uncertainties in the global budgets of all three gases still exist. Increasing use is being made of isotopic ratio measurements to untangle the separate contributions from different processes. For instance, carbon in plants has a different isotopic ratio than oceanic carbon. The oxygen isotopic ratio of CO 2 partially reflects oxygen fractionation occurring in the hydrological cycle.