Five years of nitrogen dioxide measurement with diffusion tube samplers at over 1000 sites in the UK

In 1993, a large (>1000 monitoring sites) co-ordinated monitoring network for nitrogen dioxide, using diffusion tube samplers, was established in urban areas throughout the UK. The primary aim of this network is to assess the spatial and temporal distribution of NO2 throughout the UK and highlight areas of high concentration which may require more detailed monitoring with automatic analysers. This paper presents a summary of the results for the first 5-years of monitoring, 1993–1997 inclusive. The network has shown that highest concentrations occur in London and urban areas of Yorkshire and Humberside and the East and West Midlands of the UK. Averaged over the whole of the UK, NO2 concentrations have been remarkably similar for most of the 5 years, though a significant decrease was observed at urban background locations in 1997. Overall, average NO2 concentrations during 1997 were 23 ppb at kerbside locations and 13 ppb at urban background locations. The results of the network have been used by the Department of Environment, Transport and the Regions as one of the criteria for the selection of priority areas for expansion of the UK Automatic Urban Network in recent years. Extensive quality assurance and control procedures incorporated into the network ensure that the estimated accuracy of the data is broadly comparable with the accuracy requirement for indicative monitoring specified in the EU “daughter” Directive for NO2 (±25%). The complete dataset of results for the network can be found on the world wide web at http://www.environment.detr.gov.uk/airq/aqinfo.htm.