2. In zones in which the levels of pollutants in ambient air are below the respective target values specified in Sections 1 and 2 of Annex I, Member States shall take the necessary measures not entailing disproportionate costs to maintain those levels below the target values.
Member States shall endeavour to attain the long-term objectives for ozone specified in Section 2 of Annex I, and, once attained, shall endeavour to maintain the ozone levels below those long-term objectives in so far as factors including the transboundary nature of ozone pollution, volatile organic compounds from biogenic sources and meteorological conditions so permit, and provided that any necessary measures do not entail disproportionate costs.