Pollutionwatch: December 2007

Conditions in December divided the month into three distinct periods. The first and last 10 days of the month saw wet, windy and generally unpleasant conditions holding sway over most of the country. The rain and strong winds keeping air pollution well dispersed with the only problems being in Port Talbot in Wales and Marylebone Road in London. On the 11th however, a strong anticyclone developed over the UK and by the following day this had grown to form a huge ridge of high pressure stretching from the north of Scandinavia, right down through France and Spain into northern Africa. This system remained dominant over Europe for the next 10 days. It led to clear skies and light winds that brought cold air down from the Arctic. At night temperatures across the UK were dropping as low as minus10 degrees. These conditions led to a classic winter pollution episode. Cold air close to the ground kept pollution trapped in, and with little or no wind, pollution concentrations rose rapidly over most of the country - particularly in towns and close to roads. The worst day was the 12th, when particle concentrations at 13 monitoring sites across the country broke the air quality standards, and Camden saw concentrations rise into the 'High' band. Concentrations then reduced slightly (although still remaining significantly elevated) before peaking a second time between the 19th and 21st. From the 22nd onwards a new series of weather systems began moving in from the Atlantic again bringing wet and windy, but clean conditions to the country until the end of the month.