Formaldehyde (CH2O) is a ubiquitous component of both the remote background atmosphere as well as the polluted urban atmosphere. This important trace gas is directly emitted from hydrocarbon combustion sources and from oxidation of natural hydrocarbons emitted by plants and trees. Once in the atmosphere, CH2O decomposes by several mechanisms to produce the important hydrogen radical HO2 and carbon monoxide (CO). In producing HO2, CH2O affects the partitioning among odd hydrogen radicals (HOx = [H] + [OH] + [HO2]), which through rapid reactions with hydrocarbons, control the oxidation capacity of the atmosphere. As many hydrocarbon oxidation reactions proceed through CH2O as an intermediate, CH2O also becomes important in further testing our understanding of hydrocarbon reaction mechanisms. Highly accurate measurements of CH2O throughout the mid to upper troposphere are thus critical for improving our understanding of tropospheric photochemistry.
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