Original sentence: Despite some improvement, smoke pollution was still a visible problem since the new law did not cover smaller businesses and domestic users - 97% of homes still used coal.Early efforts had relied on education such as teaching people how to build cleaner fires - but this had almost no impact.It was soon realised that real improvement would only come about by switching to a cleaner fuel -  gas, oil, coke, or anthracite were all considered but ruled out on cost grounds
Edited sentence: Despite some improvement, smoke pollution was still a visible problem since the new law did not cover smaller businesses and domestic users – 97% of homes still used coal.Early efforts had relied on education such as teaching people how to build cleaner fires – but this had almost no impact.It was soon realised that real improvement would only come about by switching to a cleaner fuel –  gas, oil, coke, or anthracite were all considered but ruled out on cost grounds