Abstract.The fate of nitrogen oxide pollution during high-latitude winter is controlled by reactions of dinitrogen pentoxide (N 2 O 5 ) and is highly affected by the competition between heterogeneous atmospheric reactions and deposition to the snowpack. MISTRA (MIcrophysical STRAtus), a 1-D photochemical model, simulated an urban pollution plume from Fairbanks, Alaska to investigate this competition of N 2 O 5 reactions and explore sensitivity to model parameters. It was found that dry deposition of N 2 O 5 made up a significant fraction of N 2 O 5 loss near the snowpack, but reactions on aerosol particles dominated loss of N 2 O 5 over the integrated atmospheric column. Sensitivity experiments found the fate of NO x emissions were most sensitive to NO emission flux, photolysis rates, and ambient temperature. The results indicate a strong sensitivity to urban area density, season and clouds, and temperature, implying a strong sensitivity of the results to urban planning and climate change. Results suggest that secondary formation of particulate (PM 2.5 ) nitrate in the Fairbanks downtown area does not contribute significant mass to the total PM 2.5 concentration, but appreciable amounts are formed downwind of downtown due to nocturnal NO x oxidation and subsequent reaction with ammonia on aerosol particles.

Dinitrogen pentoxide, N₂O₅, is an important nighttime intermediate in the oxidation of NO_x that is hydrolysed on surfaces. We conducted a field campaign in Fairbanks, Alaska during November 2009 to measure the gradient and derive a flux (and deposition velocity) of N₂O₅ depositing to snowpack using the aerodynamic gradient method. The deposition velocity of N₂O₅ under Arctic winter conditions was found to be 0.59 ± 0.47 cm s⁻¹, which is the first measurement of this parameter to our knowledge. Based on the measured deposition velocity, we compared the chemical loss rate of N₂O₅ via snowpack deposition to the total steady state loss rate and found that deposition to snowpack is at least 1/8th of the total chemical removal of N₂O₅ that is located within the first few meters above the ground surface

Abstract. The fate of nitrogen oxide pollution during high-latitude winter is controlled by reactions of dinitrogen pentoxide (N2O5) and is highly affected by the competition between heterogeneous atmospheric reactions and deposition to the snowpack. MISTRA, a 1-D photochemical model, simulated an urban pollution plume from Fairbanks, Alaska to investigate this competition of N2O5 reactions and explore sensitivity to model parameters. It was found that dry deposition of N2O5 made up a significant fraction of N2O5 loss near the snowpack, but reactions on aerosol particles dominated loss of N2O5 over the integrated atmospheric column. Sensitivity experiments found the fate of NOx emissions were most sensitive to NO emission flux, photolysis rates, and ambient temperature. The results indicate a strong sensitivity to urban area density, season and clouds, and temperature, implying a strong sensitivity of the results to urban planning and climate change. Results suggest that secondary formation of particulate (PM2.5) nitrate in the Fairbanks downtown area does not contribute significant mass to the total PM2.5 concentration, but appreciable amounts are formed downwind of downtown due to nocturnal NOx oxidation and subsequent reaction with ammonia on aerosol particles.

Dinitrogen pentoxide, N₂O₅, is an important nighttime intermediate in oxidation of NO_x that is hydrolysed on surfaces. We conducted a field campaign in Fairbanks, Alaska during November, 2009 to measure the flux (and deposition velocity) of N₂O₅ depositing to snowpack using the aerodynamic gradient method. The deposition velocity of N₂O₅ under Arctic winter conditions was found to be 0.59 ± 0.47 cm/s, which is the first measurement of this parameter to our knowledge. Based on the measured deposition velocity, we compared the chemical loss rate of N₂O₅ via snowpack deposition to the total steady state loss rate and found that deposition to snowpack is a significant fraction of the total chemical removal of N₂O₅ measured within a few meters of the ground surface

• No significant change in the overall temperature sensitivity of high northern latitude spring greenness in the past 40 years • Decreased spatial coherence of spring temperature anomalies has increased the influence of atmospheric transport on surface CO2 data • Temperature sensitivity of spring carbon uptake remains strong when accounting for atmospheric transport Accepted Article This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as