# The Air Quality Standards (Wales) Regulations 2007, Paragraph 12


The uncertainty (expressed at a 95 % confidence level) of the methods used for the assessment of ambient air concentrations must be evaluated in accordance with the CEN Guide to the Expression of Uncertainty in Measurement (ENV 13005-1999), the methodology of ISO 5725:1994, and the guidance provided in the CEN Report, “Air quality — Approach to uncertainty estimation for ambient air reference measurement methods” (CR 14377:2002E). The percentages for uncertainty in the above table are given for individual measurements, which are averaged over typical sampling times, for a 95 % confidence interval. The uncertainty of the measurements should be interpreted as being applicable in the region of the appropriate target value. Fixed and indicative measurements must be evenly distributed over the year in order to avoid skewing of results.

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Source: https://www.legislation.gov.uk/wsi/2007/717/schedule/8/paragraph/12 (the official version)
Page: https://openlegislation.uk/air-quality-standards-wales-regulations-2007/schedule-8/paragraph-12
Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.