Abstract
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 NOx in high latitude plumes.
Highlights
Tropospheric pollutants such as ozone and nitric acid (HNO3) are of growing concern due to their environmental impacts and associated health concerns
To characterize N2O5 removal mechanisms at high latitudes, we measured N2O5 using offaxis cavity ring-down spectroscopy (Ayers et al, 2005). With these data and measurements of aerosol particles and ice saturation conditions, we demonstrate that ice is largely responsible for catalyzing N2O5 heterogeneous hydrolysis at high latitudes
We have presented the first direct observations implicating ice as being the surface that catalyzes heterogeneous hydrolysis of N2O5 in the cold, nighttime boundary layer at high latitudes
Summary
Tropospheric pollutants such as ozone and nitric acid (HNO3) are of growing concern due to their environmental impacts and associated health concerns. The rapidly cycling family referred to as NOx (=nitric oxide, NO+nitrogen dioxide, NO2), play a critical role in the production of ozone and HNO3 in the troposphere. NOx oxidation and removal limits the extent to which catalytic production of ozone occurs. Deposition of HNO3 generated by NOx oxidation results in acid deposition and nitrogen fertilization, potentially altering soil and surface water nutrients and pH and causing changes in biota in sensitive ecosystems (Fenn et al, 2003; Bergholm et al, 2003; Allan et al, 1999; Heintz et al, 1996; Andersen and Hovmand, 1995)
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