Halocarbon Emissions from the United States and Mexico and Their Global Warming Potential

We use recent aircraft measurements of a comprehensive suite of anthropogenic halocarbons, carbon monoxide (CO), and related tracers to place new constraints on North American halocarbon emissions and quantify their global warming potential. Emissions continue for many compounds restricted under the Montreal Protocol, and we show that halocarbons make up an important fraction of the total greenhouse gas source for both countries: our best estimate is 9% (uncertainty range 6-12%) and 32% (21-52%) of equivalent CO₂ emissions for the U.S. and Mexico, respectively, on a 20 year time scale. Ongoing methylchloroform emissions are significant in the U.S. (2.8 Gg/y in 2004-2006), in contrast to bottom-up estimates (<0.05 Gg), with implications for tropospheric OH calculations. Mexican methylchloroform emissions are minor. For more details see Millet et al., 2009.

New Constraints on Terrestrial and Oceanic Sources of Atmospheric Methanol

Methanol is the most abundant non-methane organic gas in the atmosphere, and a significant global source of tropospheric CO and formaldehyde. We use a global 3D chemical transport model (GEOS-Chem) to interpret new aircraft, surface, and oceanic observations in terms of the constraints that they place on the atmospheric methanol budget. We find that the marine biosphere is a large source of methanol to the atmosphere, comparable to terrestrial vegetation, and is also a large sink. Aircraft measurements in the North American boundary layer reveal that terrestrial plants are a much weaker source than is presently thought, and that the anthropogenic source of methanol must be small. For more details see Millet et al., 2008.