# The Air Quality Regulations 1997, Paragraph 2: Interpretation


“ppm” means parts per million by volume.

---
Source: https://www.legislation.gov.uk/uksi/1997/3043/schedule/paragraph/2 (the official version)
Page: https://openlegislation.uk/air-quality-regulations-1997/schedule/paragraph-2
Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.