Diffusion tube data have not been used by the Department in assessing the air quality in the Heathrow area as part of the Project for the Sustainable Development of Heathrow. Diffusion tube data may be useful for trend analysis but are not deemed appropriate for the purpose of monitoring compliance. The EC Directive and UK air quality objectives require the use of automatic analysers.
The reference method for assessing the concentration of nitrogen dioxide to demonstrate compliance with EU air quality legislation is given in Directive 1999/30/EC as that defined in ISO 7996: 1985 “Ambient air—determination of the mass concentration of nitrogen oxides—chemiluminescence method”. A member state may however use any other method which it can demonstrate gives equivalent results. Data from the Automatic Urban and Rural Network (AURN) are used to fulfil the UK’s obligations to monitor nitrogen dioxide concentrations in air and to report the results to the European Commission. The AURN has 94 urban and 16 rural nitrogen dioxide monitoring stations, all of which use the chemiluminescence method.