# The Air Quality Standards (Wales) Regulations 2007, Paragraph 8


Sampling points should in general be sited so as to avoid measuring very small micro-environments in their immediate vicinity. As a guideline, a sampling point should be representative of air quality in surrounding areas of no less than 200 m2 at traffic-orientated sites, at least 250 m ×; 250 m at industrial sites, where feasible, and several square kilometres at urban-background sites.

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Source: https://www.legislation.gov.uk/wsi/2007/717/schedule/5/paragraph/8 (the official version)
Page: https://openlegislation.uk/air-quality-standards-wales-regulations-2007/schedule-5/paragraph-8
Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.