[londons_explore]

I would like to see an auto-adjusting tax...

Eg. "The tax per gram of PM2.5 is $1. Each year, if average PM2.5 levels across America are above 5 ug/m^3, the tax will increase 10%. Otherwise, it will decrease 10%."

Then lawmakers once need to put in place the tax and set the target, and they never need to intervene again.

[XorNot]

If someone is flooding the area around them with high PM2.5 thus that everyone nearby has respiratory problems, but the overall rate of PM2.5 across all of the US is very low (because generally, it actually is) then your proposed scheme would ensure that areas (generally cities) are going to be completely unlivable, but there'd be no reason to change because overall the tax would remain low.

In fact they'd have no reason to improve anything provided that their projection for the cost of improvement looked marginally more expensive then just paying projected future cost of the tax.

[WalterBright]

That's a far more practical solution that the usual EPA regulations.