The implications of results from a local authority inter-laboratory comparison of NO₂ measurement by passive diffusion tube

Four laboratories were contracted independently by the City of Edinburgh Council to prepare and analyse passive diffusion samplers for measurement of nitrogen dioxide (NO₂) during ten 1-week exposures at a kerbside location in Edinburgh. All exposures were performed in triplicate. The results showed significant differences both in the precision and the magnitude of the NO₂ measurement between the laboratories. The median relative standard deviation (RSD) for all triplicate exposures was 12% (n = 40), and the average RSD in mean NO₂ concentration between the four laboratories was 20% (n = 10). Other problems encountered during the inter-comparison are also reported, and the implications of all the findings for local authorities undertaking air quality reviews for NO₂ by this approach are discussed. It is concluded that it appears very important for each local authority to conduct their own replicate and inter-comparison studies. This article is also to be published in the Royal Environmental Health Institute of Scotland's magazine.