When Steve Marsland was a schoolboy in the sixties his walk to school in Denton was often through a thick smog which wrapped around buildings dyed a dingy grey by soot in the air.
Sulphur dioxide from burning coal would react with fog droplets, producing a toxic yellow suspension of sulphuric acid, creeping its way into eyes and lungs.
“Every terraced house had a chimney that belched out coal smoke, so did every factory,” he recalls.
