Frequently Asked Questions

  • Are there any statistics available for the error/tolerance of provisional data from automatic monitoring sites within London?

    The accuracy of air quality monitoring data are not routinely calculated. The approach taken is that data from monitoring stations operated using rigorous and approved QA/QC procedures will meet the requirements of the EU on measurement uncertainty. ERG ( has estimated the 'best possible' uncertainty for typical analysers used to measure gaseous pollutants in the London Air Quality Network. The measurement uncertainty was estimated at 5% to 7% (2ó) for NOx at high concentrations. Several operational factors were not included and these figures are likely to be under estimated. As a result of such uncertainty assessments, the London Air Quality Network has adopted a working uncertainty of ±10% for the measurements of NOx, NO2 and O3 concentrations at the EU limit value concentrations.

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