The Role Of Ice Surfaces In Affecting Nighttime Removal Of Nitrogen Oxides In High Latitude Plumes

Abstract

Nitrogen oxides play an important role in the atmosphere by affecting ozone-mediated oxidation pathways. Nitrogen oxide removal from the atmosphere occurs via nitric acid formation. This nitric acid deposits to Earth's surface, leading to acidification and nitrogen fertilization. Under dark and cold conditions that commonly exist in the winter at high latitudes, nighttime reactions oxidize NO2 to the nitrate radical, NO3, and these molecules react to form N2O5. The heterogeneous hydrolysis of N2O5, which is catalyzed by surfaces, forms nitric acid. Modeling studies indicate that a majority of the Nx removal at high latitudes results from nighttime N2O5 chemistry. The N2O5 intermediate molecules may react on snowpack surfaces or on atmospheric particles. Past field studies demonstrated that aerosol surfaces are not solely responsible for the removal of N2O 5 near Earth's surface at high latitudes. In this work, we have used aerodynamic gradient micrometeorological methods to measure the deposition velocity of N2O5 to snowpack. This measurement is the first time that snowpack deposition has been quantified directly. We have found that snowpack deposition near Earth's surface at high latitudes is a significant chemical loss process for N2O5. Further studies demonstrated higher mixing ratios and longer lifetimes of N2 O5 aloft. Increasing N2O5 abundance and longevity with altitude implicates different loss mechanisms contribute at various altitudes in the atmosphere. Near Earth's surface, N2O 5 is very reactive, while aloft it acts more as a reservoir species that can transport further. Understanding the controlling mechanisms for N x removal under high latitude conditions will lead to better characterization of the NOx transport in pollution plumes and nitric acid deposition patterns.