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.

Pollutionwatch: November 2007

November is traditionally the worst month in the UK for particle pollution due to smoke from fireworks and bonfires. However, winter conditions also led to repeated pollution episodes throughout the month. The effects of pollution from Guy Fawkes' night is heavily influenced by two main factors. Firstly, weather conditions determine if the pollution is dispersed by the wind or washed out by the rain. Secondly, if the 5th of November is on or close to a weekend, the majority of firework events will happen around the same time - greatly increasing the concentrations of pollution being put into the air. If, however, it lies in the middle of the week, events are spread across the week, and the two weekends either side, greatly reducing the pollution load at any one time. This year the 5th was on the Monday, and high pressure brought cold, calm conditions which led to huge peaks in pollution on the Saturday, Sunday and Monday nights. On the Sunday night, the air quality standard for particles was broken at 32 out of the 55 particle monitoring stations in the UK monitoring network, with 5 sites recording 'high' concentrations and 4 recording 'very high' levels. The worst affected places were in the middle of the UK, in Manchester, Leicester, Stoke and Nottingham. Following a spell of unsettled weather, another area of high pressure passed across the UK leading to spells of 'high' pollution in both London and Scotland between the 14th and the 20th. Then to round the month off, Marylebone Road in London saw 'moderate' levels of particles on the 27th and Port Talbot in Wales had 'high' levels on the 30th.