Northern Hemisphere trends in carbon monoxide: effects of changing anthropogenic emissions and biomass burning
Abstract
While the magnitude and direction of changes in tropospheric carbon monoxide (CO) during the past century are still debated; it is most likely that there have been extended periods of increase and decrease, overlaid with much shorter lived changes. The most compelling evidence for a long-term trend in the Northern Hemisphere (NH) comes from a comparison of column measurements determined above the Swiss Alps in the early 1950s and again in the mid-1980s which suggested an increase of ~1% yr-1. Quasi-continuous spectral measurements above Europe and western Russia show increasing column abundances in the 1970s through the mid-1980s, after which CO decreased at a similar rate through the mid-1990s. Several studies have shown declines in NH CO over the past two decades. Carbon monoxide has been measured in air samples collected by the NOAA Cooperative Air Sampling Network since 1988. The results provide a spatial and temporal picture of CO in the marine boundary layer which is used to identify zonal changes. The data suggest a long-term decrease in CO in the NH, with the greatest changes occurring in the 30-90 degree zonal band. Smaller decreases were found in the low Northern and Southern Hemispheres. The primary sources of CO in the NH are roughly evenly distributed between fossil fuel combustion and industrial emissions (FF), oxidation of methane and non-CH4 hydrocarbons, and biomass burning (BB); its major sink is OH. Here we examine how changes in FF and BB emissions have impacted CO in the lower troposphere. A strong decrease in anthropogenic emissions from Annex_1 countries in the early 1990s contributed to a significant decline in its abundance. Continuing declines in their emissions during the late 1990’s and 2000’s added to the downward trend despite increasing emissions from developing nations. The NH decrease in background CO during 1990-2005 (i.e. change determined without effects of the 1998/2003 fires) compares well with FF emissions inventories. Of the major CO sources only BB exhibits large inter-annual variation. While these variations obscure any trend in emissions, intense periods of biomass burning (such as those which occurred in 1997-1998 and in 2002-2003) are clearly evident in the measurements and are compared to emission estimates. The ability of the atmosphere to remove large pulses of CO suggests the troposphere is well buffered by OH.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFM.A51D0155N
- Keywords:
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- 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE;
- 0322 ATMOSPHERIC COMPOSITION AND STRUCTURE / Constituent sources and sinks;
- 3399 ATMOSPHERIC PROCESSES / General or miscellaneous