Model analysis of the factors regulating the trends and variability of carbon monoxide between 1988 and 1997 B. N. Duncan1,2 and J. A. Logan3 1Goddard Earth Sciences and Technology Center, University of Maryland at Baltimore County, Baltimore, MD, USA 2NASA Goddard Space Flight Center, Code 613.3, Greenbelt, MD, USA 3School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, USA
Abstract. We used a 3-D model of chemistry and transport to investigate trends and
variability in tropospheric carbon monoxide (CO) for 1988–1997 caused by
changes in the overhead ozone column, fossil fuel emissions, biomass burning
emissions, methane, and transport. We found that the decreasing CO burden in
the northern extra-tropics (−0.85%/y) was more heavily influenced by the
decrease in European emissions during our study period than by the similar
increase in Asian emissions, as transport pathways from Europe favored
accumulation at higher latitudes in winter and spring. However, the opposite
trends in the CO burdens from these two source regions counterbalanced at
lower latitudes. Elsewhere, the factors influencing CO often compete,
diminishing their cumulative impact, and trends in model CO were small or
insignificant for our study period, except in the tropics in boreal fall
(1.1%/y), a result of emissions from major fires in Indonesia late in
1997. There was a decrease in the ozone column during the study period as a
result of the phase of the solar cycle and the eruption of Pinatubo in 1991.
This decrease contributed negatively to the trend in model CO by increasing
the hydroxyl radical (OH). The impact of this negative contribution was
diminished by a positive contribution of similar magnitude from increasing
methane. However, the trends in these two factors did not cancel for
tropospheric OH, which responded primarily to changes in the ozone column.
Citation: Duncan, B. N. and Logan, J. A.: Model analysis of the factors regulating the trends and variability of carbon monoxide between 1988 and 1997, Atmos. Chem. Phys., 8, 7389-7403, doi:10.5194/acp-8-7389-2008, 2008.