# The Air Quality Limit Values (Scotland) Regulations 2001, Paragraph 2.2: Alert threshold for nitrogen dioxide


400μg/m3 measured over three consecutive hours at locations representative of air quality over at least 100 km2 or an entire zone or agglomeration, whichever is the smaller.

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Source: https://www.legislation.gov.uk/ssi/2001/224/schedule/1/part/II/paragraph/2n2 (the official version)
Page: https://openlegislation.uk/air-quality-limit-values-scotland-regulations-2001/schedule-1/part-II/paragraph-2n2
Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.