Cold winters can lead to higher pollution levels

Friday 18th Mar 2011 by theWeatherclub

A new study from the University of Gothenburg has shown that there is a strong link between climate and air pollution. Differences in air pressure over the North Atlantic have meant that for the last two years Gothenburg in Sweden has suffered extremely cold winters. This in turn has led to the air in Gothenburg suffering its highest ever levels of nitrogen oxides.

The winter weather in large parts of north-west Europe is influenced by the North Atlantic Oscillation (NAO) – the differences in air pressure over various regions of the North Atlantic. The NAO swings between positive and negative phases depending on the differences in air pressure between Iceland and the Azores. When the NAO is in a negative phase – as has been the case during the last two winters – Gothenburg has cold winters because the low pressure sits over southern Europe, while cold air from the polar region or Siberia sits over northern Europe

A study carried out by a group of researchers from the University of Gothenburg investigated how the concentrations of nitrogen oxide and nitrogen dioxide (NO and NO2) in the air can be linked to the weather. Published in the scientific journal Atmospheric Environment, the study shows that the air quality standard has been exceeded more and more frequently during periods of a negative NAO even though emissions have fallen in the city centre since 2000.

“These extremely cold winters in Gothenburg, with high cold air, bring a clear deterioration in air quality," says Maria Grundström 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." Air mixing is often poor in the city during the months when the NAO is negative. This means that air pollution emitted at ground level accumulates significantly reducing air quality. During the winter months of 1997 to 2006, concentrations of nitrogen oxides were around 18% higher during months when the NAO was negative than when it was positive.

While the study was centred on the experience of one city, it does have a far wider relevance. As well as adding to our knowledge of how weather conditions interact with emissions, it also has an impact on how we measure our efforts at reducing them.  By showing that weather conditions can cause concentrations of some types of emission-based pollution to rise at the same time as the levels of those emissions are falling, the study reminds us of the complexities inherent within climate science. It reminds us of the need to keep a very close eye on how current conditions fit in with long term trends. Finally it reminds us that there will be times when effects of man-made climate change will be taken out of mankind’s control altogether.