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While the hydroxyl radical (<mo>•</mo>OH) in the snowpack is likely adominant oxidant for organic species and bromide, little is known about thekinetics or steady-state concentrations of <mo>•</mo>OH on/in snow andice. Here we measure the formation rate, lifetime, and concentration of<mo>•</mo>OH for illuminated polar snow samples studied in the laboratoryand in the field. Laboratory studies show that <mo>•</mo>OH kinetics andsteady-state concentrations are essentially the same for a given samplestudied as ice and liquid; this is in contrast to other photooxidants, whichshow a concentration enhancement in ice relative to solution as a result ofkinetic differences in the two phases. The average production rate of<mo>•</mo>OH in samples studied at Summit, Greenland, is 5 times lowerthan the average measured in the laboratory, while the average <mo>•</mo>OH lifetime determined in the field is 5 times higher than in thelaboratory. These differences indicate that the polar snows we studied in thelaboratory are affected by contamination, despite significant efforts toprevent this; our results suggest similar contamination may be a widespreadproblem in laboratory studies of ice chemistry. Steady-state concentrationsof <mo>•</mo>OH in clean snow studied in the field at Summit, Greenland,range from (0.8 to 3) × 10−15 M, comparable to values reportedfor midlatitude cloud and fog drops, rain, and deliquesced marine particles,even though impurity concentrations in the snow samples are much lower.Partitioning of firn air <mo>•</mo>OH to the snow grains willapproximately double the steady-state concentration of snow-grain hydroxylradical, leading to an average [<mo>•</mo>OH] in near-surface, summerSummit snow of approximately 4 × 10−15 M. At this concentration,the <mo>•</mo>OH-mediated lifetimes of organics and bromide in Summit snowgrains are approximately 3 days and 7 h, respectively, suggesting thathydroxyl radical is a major oxidant for both species

Hydroxyl radical in/on illuminated polar snow: formation rates, lifetimes, and steady-state concentrations