Smokestack is the names for a chimney. He's saying in the past general smoke in the area means he couldn't see the chimneys or beyond, but now the site is decom

Smokestack is the names for a chimney. He's saying in the past general smoke in the area means he couldn't see the chimneys or beyond, but now the site is decommissioned (and I assume other heavy industries have gone), the air quality is better and he can see from the rhet.