Atmospheric Trends of Carbon Monoxide (CO) by Khalil and Rasmussen

Carbon monoxide (CO) is a weak greenhouse gas but it is an important precursor to tropospheric ozone (O3) and other trace gases in the Earth's atmosphere, which can cause widespread changes in tropospheric chemistry, global warming, and other climatic changes. Hydroxyl (OH) radicals in the global atmosphere are removed primarily through reactions with CO. OH radicals remove many man-made and natural trace gases from the atmosphere including halocarbons and hydrocarbons. Increases in CO may lead to decreases in OH allowing manmade and natural trace gases to build up in the atmosphere. Nearly half of the estimated amount of CO in the atmosphere is due to anthropogenic sources such as automobile emissions, fossil fuel combustion, and biomass burning (Logan et al, 1981). Concentrations of CO have probably doubled since pre-industrial times and is increasing at an annual rate between 0.8% and 1.4% (Khalil and Rasmussen, 1988). Khalil and Rasmussen at the Oregon Graduate Institute have collected over 60,000 CO measurements from the remote site at Cape Meares, Oregon on the Pacific coast (Khalil and Rasmussen, 1984) from 1979-1983. CO was measured using an automated gas chromatograph equipped with a methanotor and flame ionization detector. Later observations were obtained at other sites around the globe including Barrow (Alaska), Cape Meares (Oregon), Hawaii(Cape Kumukahi and Mauna Loa), American Samoa (Pacific Ocean), Tasmania (Australia), Mawson (Antarctica) and South Pole. The database consists of monthly CO concentrations in parts per billion by volume (ppbv) from ecah site including observations from Cape Meares (1979-1983). A global average CO concentration was determined from trend analyses of the data collected at these sites.