The whole approval thing was a bit of a farce from the beginning. A whole lot were approved after testing without a wetback then people installed them with a wetback (which takes a lot of heat from the combustion chamber) and the emissions were a lot higher. There have since been a few invented which cannot pass approval, even though their emissions are far better than the approved ones, because their loading methods are different to those required by the test. They need to change the test but they are too busy supporting the land developers that want to get rich from creating thousands more sections than the City needs. Christchurch is the only city I know of where the expensive land is by the airport and the cheap stuff is by the sea.