Pollutionwatch: April 2007

With the above average sunshine and exceptionally warm weather throughout much of April, it was little surprise to find that the summer smog season has started. On the 27th the government issued its first summer smog warning of the year for the final weekend of the month. Despite the warning, the predicted 'high' concentrations of ozone failed to materialise. 'Moderate' levels were reported from over a dozen monitoring stations on the 28th, 29th and 30th, however, this was a small handful compared to the 40+ stations reporting moderate concentrations earlier in the month on the 1st, 2nd, 15th and 21st (when no warning was given). This demonstrates one of the main difficulties in forecasting air pollution levels - particularly when the purpose is both to provide health warnings and to encourage people to avoid or reduce polluting activities, such as driving, having bonfires or barbeques, or using solvent based paints and varnishes. When a warning is issued in the approach to a predicted episode, if the predicted high concentrations fail to materialise it is impossible to tell whether there was a problem in the forecast, or if sufficient people heeded the advice and reduced polluting emissions sufficiently to avoid the problem. In addition to the ozone problems there was also a minor particle episode between the 12th and the 16th. Concentrations rose across most of the UK, and up to seven sites broke the air quality standards on each day. The increase in regional levels meant that concentrations were pushed into the 'high' band near to the steelworks in Port Talbot where moderate concentrations are frequently recorded.