In a nutshell, Texas has a flexible standard for permitting air pollution. Say it is your home (it isn't - this is for example only). You have a super clean furnace and super clean heaters but you insist on a coal fired fireplace. The EPA would say yes yes and no - grading and evaluating each individual part while Texas would say "overall it is ok" - taking a "in total approach" to your home rather than each emitting part of it.
The EPA started warning Texas about this years ago and of course Texas so "our way or the highway" to the EPA. The EPA is going to win and now Texas is screaming because of it.
The air in Houston is so bad as to be toxic on many days. There are plenty of profits to make money available to keep things clean or start to keep things clean. But then again the EPA is standing there between the pig and the trough and now with the GOP loaded congress, .... well the phrase "don't hold your breath" has new meaning.