"The 2008 Ambient Air Quality Directive sets legally binding limits for concentrations in outdoor air of major air pollutants that affect public health such as particulate matter (PM10 and PM2.5) and nitrogen dioxide (NO2)."
Published 6 March 2014
Last updated 1 November 2019
From: Ministry of Housing, Communities & Local Government
https://www.gov.uk/guidance/air-quality--3
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