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The daily air quaity index changed on the 1st of January 2012.
This map shows a pollution "nowcast", which is a pilot service to show current pollution levels in detail across London in comparison with the Government's Air Pollution Index.
It is created by combining readings taken within the last hour and air pollution modelling in London. As you zoom into the map you will see which areas are currently experiencing higher pollution levels than others, usually those areas close to busy roads. More information about the Air Pollution Index and health advice associated with each index level can be seen here.
- Why nowcast?
Measurements from monitoring stations are only able to report air quality at that particular place. The nowcast combines these measurements with our detailed model to show a prediction of what air quality is like across the whole of Greater London.
- Why do you show only three pollutants?
The three pollutants chosen are ones which are known to have an effect on health within London and are able to be predicted with this model. Levels of carbon monoxide (CO) are now below those considered to be harmful to health, and emissions of sulphur dioxide (SO2) are too unpredictable to create a map using this method.
Each pollutant has different sources and behaviour, so try selecting each pollutant in turn to get a full picture of air quality at your chosen location.
- Why does pollution appear to be low everywhere?
Often air pollution levels in most areas of London are sufficiently small to be classified as low according to the air quality index. When this index was created these levels were considered unlikely to cause any adverse health effects. There is currently debate about whether there is any safe level for these pollutants, and there are plans to update the index soon. Much of the pollution in London is associated with traffic and zooming in to show individual roads will usually reveal locations where pollution levels are higher.
- How accurate is it?
Based on comparison of nowcast and measurements from monitoring sites we expect the nowcast to be a good visualisation of measured data to within half an index value for most locations. The 20m resolution of the model is not able to fully represent pollution concentrations within a few metres of roads and very localised sources of PM10. We will be monitoring the performance of the nowcast and expect to be adjusting and improving it over time. A more in depth evaluation of nowcast accuracy is available here.