ATMOSPHERIC CHEMISTRY

Alcohol Can Impair Measurement

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Science  12 Apr 2002:
Vol. 296, Issue 5566, pp. 221
DOI: 10.1126/science.296.5566.221a

Oxidation reactions involving hydroxyl radical (OH) and hydrogen dioxide (HO2)—collectively known as HOx—play an important role in atmospheric chemistry by destroying many pollutants. However, because their concentrations are very low, on the order of parts per trillion, it has been difficult to obtain reliable data on HOx at remote locations. Measurements of hydrogen peroxide (H2O2) would allow an estimate of HOx concentration, because the reaction of two HO2 molecules to form H2O2 and O2 is the main source of H2O2 in the upper troposphere and the stratosphere. Unfortunately, balloon-borne measurements have produced lower H2O2 concentrations in the stratosphere than those predicted by models, indicating that the current understanding of the kinetics governing the production and loss of H2O2 is incomplete.

Christensen et al. have refined the rate constant for the H2O2 formation reaction from HO2. Accounting for the effect of methanol (which often is used as a precursor for HO2) on the formation reaction yields a rate constant lower than the one currently recommended, especially at low temperatures. When the adjusted rate constant was used in a photochemical simulation, good agreement with measured H2O2 was obtained.—JU

Geophys. Res. Lett.29, 10.1029/2001GL0114525 (2002).

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