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# Long description

This is a map showing nitrogen dioxide concentrations in London. It covers an area approximately 50 kilometres from east to west and 30 kilometres from north to south. Central London is shown in the middle with Heathrow Airport visible at the lower left. The annual mean nitrogen dioxide concentration is shown by colour. A legend at the right shows yellow as indicating a level of between 15 and 20 microgrammes per cubic metre, light orange 20 to 25 microgrammes, orange 25 to 30 microgrammes, light pink 30 to 35 microgrammes, pink 35 to 40 microgrammes, light purple 40 to 45 microgrammes, mid-purple 45 to 50 microgrammes, dark purple 50 to 55 microgrammes, dark purple brown 50 to 55 microgrammes and dark brown over 55 microgrammes. There is an arrow to the right of the legend indicating a limit of 40 microgrammes. The map shows that the annual mean is only below 25 microgrammes in the outer suburbs and increases towards the centre of London. Most of central London has a level of 30 microgrammes or higher. The main roads are visible on the map as purple lines, indicating high levels of nitrogen dioxide, above the limit of 40 microgrammes. There are also high levels around Heathrow airport.