The role of ice in N₂O₅ heterogeneous hydrolysis at high latitudes

Abstract. 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 (≈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. 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 NO_x in high latitude plumes.