Recent Changes in Atmospheric Carbon Monoxide

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Science  18 Mar 1994:
Vol. 263, Issue 5153, pp. 1587-1590
DOI: 10.1126/science.263.5153.1587


Measurements of carbon monoxide (CO) in air samples collected from 27 locations between 71°N and 41°S show that atmospheric levels of this gas have decreased worldwide over the past 2 to 5 years. During this period, CO decreased at nearly a constant rate in the high northern latitudes. In contrast, in the tropics an abrupt decrease occurred beginning at the end of 1991. In the Northern Hemisphere, CO decreased at a spatially and temporally averaged rate of 7.3 (±0.9) parts per billion per year (6.1 percent per year) from June 1990 to June 1993, whereas in the Southern Hemisphere, CO decreased 4.2 (±0.5) parts per billion per year (7.0 percent per year). This recent change is opposite a long-term trend of a 1 to 2 percent per year increase inferred from measurements made in the Northern Hemisphere during the past 30 years.