Abstract
Abstract. Acetylene (C2H2) volume mixing ratios (VMRs) have been successfully retrieved from the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) Level 1B radiances during August 2003, providing the first global map of such data and ratios to CO in the literature. The data presented here contain most information between 300 hPa and 100 hPa with systematic errors less than 10% at the upper levels. Random errors per point are less than 15% at lower levels and are closer to 30% at 100 hPa. Global distributions of the C2H2 and C2H2/CO ratio confirm significant features associated with both the Asian monsoon anticyclone and biomass burning for this important hydrocarbon in a characteristic summer month (August 2003), showing tight correlations regionally, particularly at lower to medium values, but globally emphasising the differences between sources and lifetimes of CO and C2H2. The correlations are seen to be particularly disturbed in the regions of highest C2H2 concentrations, indicating variability in the surface emissions or fast processing. A strong isolation of C2H2 within the Asian monsoon anticyclone is observed, evidencing convective transport into the upper troposphere, horizontal advection within the anticyclone at 200 hPa, distinct gradients at the westward edge of the vortex and formation of a secondary dynamical feature from the eastward extension of the anticyclone outflow over the Asian Pacific. Ratios of C2H2/CO are consistent with the evidence from the cross-sections that the C2H2 is uplifted rapidly in convection. Observations are presented of enhanced C2H2 associated with the injection from biomass burning into the upper troposphere and the outflow from Africa at 200 hPa into both the Atlantic and Indian Oceans. In the biomass burning regions, C2H2 and CO are well correlated, but the uplift is less marked and peaks at lower altitudes compared to the strong effects observed in the Asian monsoon anticyclone. Ratios of C2H2/CO clearly decay along transport pathways for the outflow, indicating photochemical ageing of the plumes. Overall, the data show the distinctive nature of C2H2 distributions, confirm in greater detail than previously possible features of hydrocarbon enhancements in the upper troposphere and highlight the future use of MIPAS hydrocarbon data for testing model transport and OH decay regimes in the middle to upper troposphere.
Highlights
The burning of vegetation, both living and dead, can release large quantities of gases into the atmosphere
The correlation was performed separately for the Northern are observed over this region where data are present. It is (Fig. 4b) and Southern (Fig. 4c) Hemispheres and it is apthe strong enhancement of both CO and C2H2 in the Middle East region which is of particular interest
The strong correlation of 0.92 for the of this feature is long-range transport from the convective re- Southern Hemisphere is due to the relative lack of significant gion over South-East Asia via the Easterly Jet associated with the Asian monsoon anticyclone into the Middle East
Summary
The burning of vegetation, both living and dead, can release large quantities of gases into the atmosphere. Biomass burning is a major source for the injection of trace gases into the atmosphere. Biomass burning and combustion were thought to be the major sources of acetylene (C2H2) (Hegg et al, 1990; Blake et al, 1996; Whitby and Altwicker, 1978). Recent work proposes biofuel emissions as the dominant source with Xiao et al (2007) estimating that as much as half of global C2H2 is biofuelrelated (3.3 Tg yr−1) with the remainder due to fossil fuel (1.7 Tg yr−1) and biomass burning (1.6 Tg yr−1). Streets et al (2003) make a clear distinction between open biomass burning (i.e. forest fires) and the combustion of biofuels (wood, crop residue, dung, etc.) in domestic cooking and heating.
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