The role of ice in N 2 O 5 heterogeneous hydrolysis at high latitudes

We report evidence for ice catalyzing N2O5 heterogeneous hydrolysis from a study conducted near Fairbanks, AK in November 2007. Mixing ratios of N2O5, NO, NO2, and ozone are reported and are used to determine steady state N2O5 lifetimes. When air masses are sub-saturated with respect to ice, the data show longer lifetimes (≈20 min) and elevated N2O5 levels, while ice-saturated air masses show shorter lifetimes (≈6 min) and suppressed N2O5 levels. We also report estimates of aerosol surface area densities that are on the order of 50 μm2/cm3, a surface area density that is insufficient to explain the rapid losses of N2O5 observed in this study, reinforcing the importance of other reactive surfaces such as ice. Ice-saturated pollution plumes are ubiquitous in high latitudes; therefore, catalysis on these surfaces is largely responsible for nocturnal processing of N2O5 leading to nitric acid production and loss of NOx in high latitude plumes.