11.—(1) The Secretary of State must, taking a cost-effective and risk-based approach, monitor the negative impacts of air pollution at sites representative of the following habitats and ecosystems—
(a)freshwater;
(b)natural and semi-natural;
(c)forest.
(2) The Secretary of State must identify sites to be monitored for the purpose of paragraph (1) by 1st July 2018 and review the suitability of those sites at least once in every four years from that date.