A strong link between the coldness of the winter and air pollution has just been established by a group of researchers from the University of Gothenburg. Nitrogen oxides levels have been much higher than usual in the Swedish city during the last two harsh winters.
They discovered that the differences in air pressure over the North Atlantic influence weather in Gothenburg and most of North-Western Europe. Those differences are called the North Atlantic Oscillation, and the pressures happen between Iceland and the Azores. When the NAO is negative, low-pressure, cold air sits over southern Europe, and cold air from the polar region or Siberia sits over northern Europe.
“These extremely cold winters in Gothenburg, with high cold air, bring a clear deterioration in air quality,” says Maria Grundstri¶m from the University of Gothenburg’s Department of Plant and Environmental Sciences, one of the researchers behind the study. “With typical Gothenburg weather — low air pressure with precipitation and strong winds — the air pollution is dispersed more quickly on account of better air mixing.”
Pollution accumulates at ground level because during these cold winters air mixing is very poor during the months when the NAO is negative. An example were the winter months of 1997 to 2006, when NO and NO2 concentrations were around 18% higher when the NAO was negative than when it was positive.