The fate of nitrogen pollution in high-latitude winter: investigations using a 1-D photochemical model

Abstract

Simulations using a 1-D photochemical model were performed to analyze the fate of NOx pollution in a high-latitude winter environment. Modeled pollution emissions were constrained by observations from downtown Fairbanks and the model reproduced dilution of NOx on timescales in agreement with field measurements on the edge and outside of the urban area of Fairbanks. The model was updated from previous versions to include calculations of reactions of N₂O₅ on aerosol particles and an empirically-derived value for dry deposition velocity of N₂O₅ to the snowpack, which acts as a competing loss of N₂O₅. It was found that dry deposition of N₂O₅ causes a significant fraction of N₂O₅ loss near the snowpack, but reactions on aerosol particles dominate loss of N₂O₅ over the total atmospheric column. Sensitivity experiment results indicate a strong sensitivity to urban area density (affecting NO flux), season and clouds (affecting photolysis), and weather and climate (affecting temperature), implying a strong sensitivity of the results to urban planning and climate change. Model simulations produced large amounts of secondary ammonium nitrate downwind of the polluted area due to NOx oxidation and subsequent reactions with ammonia on aerosol particles.