Missing Sink for Free Radicals?

In August 2010, an article was published in Nature that reported that there may be a missing sink for free radicals in our atmosphere. After taking measurements of a suite of atmospheric compounds over Alaska, northern Canada, Greenland and the North Pole, a research team found that widely used atmospheric-chemistry models tend to underestimate OH concentrations in the lowermost region of the atmosphere but overestimates OH concentrations in the upper troposphere. The authors propose that multiphase reactions on aerosol particles could be the missing sink of HO_x radicals. If correct, this could imply that that HO₂ uptake on aerosols may also be an important factor for the cold upper troposphere at lower latitudes, and not just in Arctic regions.