The North Atlantic Oscillation controls air pollution transport to the Arctic

This paper studies the interannual variability of pollution pathways from northern hemisphere (NH) continents into the Arctic. Using a 15-year model simulation of the dispersion of passive tracers representative of anthropogenic emissions from NH continents, we show that the North Atlantic Oscillation (NAO) exerts a strong control on the pollution transport into the Arctic, particularly in winter and spring. For tracer lifetimes of 5 ( 30) days, surface concentrations in the Arctic winter are enhanced by about 70% (30%) during high phases of the NAO ( in the following referred to as NAO(+)) compared to its low phases (NAO(-)). This is mainly due to great differences in the pathways of European pollution during NAO(+) and NAO(-) phases, respectively, but reinforced by North American pollution, which is also enhanced in the Arctic during NAO(+) phases. In contrast, Asian pollution in the Arctic does not significantly depend on the NAO phase. The model results are confirmed using remotely-sensed NO2 vertical atmospheric columns obtained from seven years of satellite measurements, which show enhanced northward NO2 transport and reduced NO2 outflow into the North Atlantic from Central Europe during NAO(+) phases. Surface measurements of carbon monoxide (CO) and black carbon at high-latitude stations further corroborate the overall picture of enhanced Arctic pollution levels during NAO(+) phases.