# The Air Quality (Scotland) Regulations 2000, Paragraph 1A


“PM2.5” means particulate matter which passes through a size-selective inlet with a 50% efficiency cut-off at 2.5μm aerodynamic diameter.

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Source: https://www.legislation.gov.uk/ssi/2000/97/schedule/paragraph/1A (the official version)
Page: https://openlegislation.uk/air-quality-scotland-regulations-2000/schedule/paragraph-1A
Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.