Rapid uplift of nonmethane hydrocarbons in a cold front over central Europe

The vertical distribution of 21 C2–C7 nonmethane hydrocarbons (NMHCs) has been determined in planetary boundary layer (PBL) and free tropospheric (FT) air over central Europe under a range of meteorological conditions. High-frequency whole air sampling was conducted on board the U.K. Meteorological Office C-130 Hercules aircraft during the European Export of Precursors and Ozone by Long-Range Transport (EXPORT) experiment in August 2000. When vertical transport by large-scale flow or convection was weak, the expected large concentration gradient between the PBL and FT was observed for all short and medium lifetime hydrocarbons (e.g., average iso-butane, PBL 100 pptV, FT 6 pptV). During periods of strong convective activity associated with the passage of a cold front, a rapid uplift of reactive carbon from the boundary layer to the mid free troposphere was observed. Using changing ratios of hydrocarbons with different atmospheric lifetimes, a timescale for transport during this event was determined. Hydrocarbon lifetime measurements suggest that in certain regions of the system, it is convective transport embedded within the cold front rather than larger-scale advection along the warm conveyor belt that is dominant in transporting ozone precursors into the free troposphere

Global budget of ethane and regional constraints on U.S. sources

[1] We use a 3-D chemical transport model (the GEOS-Chem CTM) to evaluate a global emission inventory for ethane (C2H6), with a best estimate for the global source of 13 Tg yr 1, 8.0 Tg yr 1 from fossil fuel production, 2.6 Tg yr 1 from biofuel, and 2.4 Tg yr 1 from biomass burning. About 80 % of the source is emitted in the Northern Hemisphere. The model generally provides a reasonable and unbiased simulation of surface air observations, column measurements, and aircraft profiles worldwide, including patterns of geographical and seasonal variability. The main bias is a 20%–30% overestimate at European surface sites. Propagation of the C 2H 6 seasonal signal from northern midlatitudes to the equatorial western Pacific and the southern tropics demonstrates the dominance of northern midlatitudes as a source of C 2H 6 worldwide. Interhemispheric transport provides the largest C2H6 source to the Southern Hemisphere (1.7 Tg yr 1), and southern biomass burning provides the other major source (1.0 Tg yr 1). The C 2H 6 emission inventory for the United States from the Environmental Protection Agency (0.6 Tg yr 1) is considerably lower than our estimate constrained by extensive aircraft observations in the continental boundary layer (2.4 Tg yr 1). This appears to reflect a factor 7 underestimate in the fossil fuel source over the south-central United States. Our estimate of C2H6 emissions, together with observed ratios of CH4:C2H6, suggests that CH4 emissions from energy production in the U.S. may be underestimated by as much as 50%–100%