FEBRUARY 2001: CO time series for 1990-1997

Comparison of observations (black line) from three NOAA/CMDL surface stations of carbon monoxide (CO) with simulated concentrations (red line) from the GEOS-CHEM global 3-D model of tropospheric chemistry for 1990-1997. Carbon monoxide is a reactive trace gas that controls the concentration of the hydroxyl radical (OH), the main tropospheric oxidant responsible for the removal of many environmentally important trace gases. This result is part of a study conducted by Bryan Duncan and Jennifer Logan to understand the year-to-year variations in CO due to interannual variations in atmospheric dynamics and chemistry, fossil fuel emissions, biomass burning patterns, and stratospheric ozone columns. The first station, in Barrow, Alaska, shows a downward trend in CO concentrations in both the model and observational data reflecting decreasing fossil fuel emissions from Russia for this time period. At the second station on the coast of Ireland, the model captures the highly variable nature of CO. This site is subjected alternately to relatively clean air from the Atlantic Ocean and to polluted air from the European continent. At the continental site of Niwot Ridge, Colorado (3 km elevation), oxidation of methane and other hydrocarbons is an important source of CO; fossil fuel emissions from Europe, North America, and Asia also contribute significantly, especially in winter.