1.In underground mining and tunnelling, Member States may benefit from a transitional period ending at the latest on 21 August 2023, as regards the limit values for nitrogen monoxide, nitrogen dioxide and carbon monoxide.
2.During the transitional period referred to in paragraph 1, Member States may continue to apply the following, instead of applying the limit values established in the Annex:
(a)in respect of nitrogen monoxide: the existing limit values established in accordance with the Annex to Directive 91/322/EEC;
(b)in respect of nitrogen dioxide and carbon monoxide: national limit values in force on 1 February 2017.