Opinion of Advocate General Kokott delivered on 17 November 2022.#European Commission v Republic of Bulgaria.#Failure of a Member State to fulfil obligations – Directive 2008/50/EC – Ambient air quality – Judgment of the Court establishing a failure to fulfil obligations – Article 260(2) TFEU – Obligation to take the necessary measures to comply with such a judgment – Failure to fulfil that obligation alleged by the European Commission – Lack of clarity of the letter of formal notice as to whether the judgment still had to be complied with on the reference date – Principle of legal certainty – Inadmissibility.#Case C-174/21.