Pollutionwatch: November 2006

Traditionally autumn runs from the equinox in September to the winter solstice in late December. Meteorologists however need to have fixed periods so that they can make year on year comparisons of seasonal weather, and it is convenient if these coincide with exact months. Their definition of autumn runs from the beginning of September to the end of November. The seasons for studying air pollution tend to be even simpler, with the pollution calendar usually split into a summer period and a winter period running from April to September, and from October through to March. Summer pollution events consist largely of photochemical pollution generated by bright sunlight, whilst winter pollution episodes are caused by cold temperature inversions and exacerbated in places by increased emissions from domestic heating. Despite November grabbing headlines as the end of the warmest autumn on record, we saw some proper winter conditions back at the start. Over the first week of the month, high pressure brought very cold conditions to the UK with temperatures dropping to minus five in Oxfordshire. This led to very stable conditions, with no wind and foggy mornings. Guy Fawkes’ night also fell on the Sunday of this week, leading to most of the related fireworks and bonfires being held over the weekend. In this weather, the smoke from the celebrations led to the worst pollution event for several years, as particle concentrations in urban centres soared. Over the weekend 19 monitoring stations recorded ‘Moderate’ levels of particles, 13 recorded ‘High’ concentrations and two sites in London and one in St Pauls in Bristol reached the ‘Very High’ band.