Unfortunately, the Congress granted the fourth branch of government effective law-making capability.
Congress passed the Clean Air Act it is USC codified law, with that the EPA has the charter and the authority to clean the air. The standards are set by best available technology for any given period of action items. Even with SCR on coal stacks they are still an order of magnitude dirtier than natural gas and infinitely dirtier than nuclear power with regards to air emissions for SCR those are NOx or the various all toxic nitrous oxides. Every one of them is toxic in some way with ppm levels being the ambient limits for humans to breathe. Coal if they cannot clean up to at least natural gas levels of emissions deserves to be shut down and left in the dust bin of history. This doesn’t even touch the heavy metals in the stacks, three of them being neurotoxins,(lead,mercury,vanadium) that coal plants even with particulate filters emit in large amounts. Plus a slew of other volatile organic particulates in the 2.5 micron or less size range the kind that get deep into human lungs and cause all kind of problems. Not just cancers, PM2.5 are small enough to cross the lungs to blood barrier and form the nucleus of blood clots as the body sees the foreign matter as hostile and attacks it with white blood cells and platelets. Pm2.5 is one of the leading causes of myocardial infarctions and strokes. Coal will never be clean , it can be cleaner but it will always pollute. The sooner humans move past it the better. Turning it into gas via a sealed gassifier is one way as the output is analytically scrubbed fuel gas into gas turbines who’s exhaust also go through SCR cats to get rid of NOx has no PM.5 matter in it as it was scrubbed to the submicron level before combustion in that turbine. Another way is to use a solid carbon fuel cell and feed it crushed micronized coal particles again since there is no direct combustion the only outputs are water,CO2 and spent carbonate salts that when reprocessed strips the ash out as a solid form not up in the air stacks as submicron sized particles.