# The Air Quality Limit Values Regulations 2001, Paragraph 1.2: Alert threshold for sulphur dioxide


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

---
Source: https://www.legislation.gov.uk/uksi/2001/2315/schedule/1/paragraph/1.2 (the official version)
Page: https://openlegislation.uk/air-quality-limit-values-regulations-2001/schedule-1/paragraph-1.2
Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.