The Secretary of State is under a duty to ensure that air quality standards are maintained, set out in regulation 17 of, and Schedule 2 to, the Air Quality Standards Regulations 2010 (S.I. 2010/1001) (“the 2010 Regulations”). For nitrogen dioxide one such limit is that levels of nitrogen dioxide must not exceed 40 micrograms per cubic metre, averaged over a calendar year. They implement the UK’s obligations under Directive 2008/50/EC on ambient air quality and cleaner air for Europe (amongst other things). They will continue to form part of UK law after the end of the implementation period on 31st December 2020 at 23:00.