# The Air Quality Regulations 1997, Paragraph 9: Interpretation


A 15 minute mean is a mean calculated every 15 minutes. The 15 minute mean for a particular substance at a particular location for a particular 15 minutes is the mean of the levels recorded, at a frequency of not less than once every 10 seconds, for that substance at that location during that 15 minutes.

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Source: https://www.legislation.gov.uk/uksi/1997/3043/schedule/paragraph/9 (the official version)
Page: https://openlegislation.uk/air-quality-regulations-1997/schedule/paragraph-9
Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.