By Sally Williams, ITV Weather presenter
On Friday some areas of London could see moderate to very high levels of air pollution.
It’s a result of the high pressure currently over us and light winds. These stagnant conditions can allow poor air to build up and linger.
The Air Quality Index uses a scale of 1 – 10 where 10 forecasts very high levels of air pollution.
When the pollution is VERY HIGH it’s advised that adults and children with lung problems, adults with heart problems, and older people, should avoid strenuous physical activity. People with asthma may find they need to use their reliever inhaler more often. It’s also suggested the general public reduce physical exertion, particularly outdoors, especially if they experience symptoms such as a cough or sore throat.
When levels are MODERATE adults and children with lung problems and adults with heart problems, who experience symptoms, should consider reducing strenuous physical activity particularly outdoors. While those who are not at risk can enjoy their usual outdoor activities.
The Air Quality Index is based on five key pollutants:
Simon Birkett, Founder and Director of Clean Air in London, said: "Londoners are literally stewing in their own juice with our own fumes trapped in still air for days. It is a stark reminder of how much we need to reduce building emissions as well as traffic emissions. Please do not burn wood on Friday!"
For explainer videos and articles on air quality and pollution go to ITV Weather's dedicated page.