The data shows roadside and background average readings for Nitric Oxide, Nitrogen Dioxide, Oxides of Nitrogen, Ozone, Particulate Matter (PM10 and PM2.5), and Sulphur Dioxide. Measured in Micrograms per Cubic Meter of Air (ug/m3). The spreadsheet shows which Index level each reading falls in, and contains charts showing pollutant levels by time of day per month.

Trend graphs of Nitrogen Dioxide and Particulate Matter PM2.5 are on the London Dashboard.

In the Mayor’s Air Quality Strategy, the Mayor adopted a policy to support the improvement of the air quality monitoring network in London so that it provides accurate and up to date information about air quality trends and current conditions in London. Publishing this data forms part of the delivery of that proposal, and also part of a larger push by the GLA towards transparency and sharing of information.

Each pollutant is measured every 15 minutes across the London Air Quality Network. Averages are calculated from these measurements. The averages shown here have been placed into the relevant DEFRA air quality index bands but are indicative only, and do not represent official air quality monitoring for European legislation.

The revised Daily Air Quality Index, published by DEFRA in April 2013, is used within this spreadsheet. More information about this can be found in DEFRA's report.

A review of the UK Air Quality Index by the Committee on the Medical Effects of Air Pollutants is available to read here.

A summary of air pollution definitions, sources, and consequences from a CIWEM report is available within the spreadsheet.

Link to GLA Air Quality page

the Mayor of London and the London Assembly