The role of ice in N2O5 heterogeneous hydrolysis at high latitudes

We report evidence for ice catalyzing N2O5 heterogeneous hydrolysis from a study conducted near Fairbanks, Alaska 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 (approximate to 20 min) and elevated N2O5 levels, while ice-saturated air masses show shorter lifetimes (approximate to 6 min) and suppressed N2O5 levels. We also report estimates of aerosol surface area densities that are on the order of 50 mu m(2)/cm(3), 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. Consideration of two possible responsible types of ice surfaces, the snowpack and suspended ice particles, indicates that both are reasonable as possible sinks for N2O5. Because ice-saturated conditions are ubiquitous in high latitudes, ice surfaces are likely to be a key loss of N2O5, leading to nitric acid production and loss of NOx in high latitude plumes.