My background is environmental consulting, not law, so take my legal analysis with ample salt. Even so, this goes way outside the area of the Clean Air Act that I deal with regularly, but here goes…
I’m drawing heavily from the Slate piece here.
Some states will not be able to meet clean air standards even if they shut down every source that contributes to ozone pollution in the state, they will never meet federal standards because upwind polluters produce enough pollution that downwind states can’t meet the standard. The Clean Air Act, the basis for a lot of stationary source air pollution regulation, contains a “good neighbor” clause that gives the CAA power to curb pollution from one state if it would impact a neighbor. Historically, the clause has been applied in a very limited way, almost a source by source basis. In 2011, the EPA passed a set of regulations that groups contributing states together with the downwind states as a Transportation Region and imposes a set of rules on them to limit the impact on downwind states.
One objection to the regulation is that it overreaches. This argument is that the “good neighbor” clause is limited to a source by source basis and cannot be applied regionally. The other argument is that the approach doesn’t do anything to distinguish small contributors from the large ones. States contributing even 1% of the total pollution can be grouped into a Transportation Region.
I can see potential for this to be overturned on the same basis that the formula in Section 4 of the Voting Rights Act was overturned last year. The wording of the good neighbor provision is vague. In theory, this could allow the EPA a lot of leeway in setting the guidelines, but the Supreme Court may find the EPA’s rulemaking too arbitrary.
To picture the way this works, think of a box canyon. Zone 1 is the mouth of the canyon, and Zone 5 is at the end of the canyon with no exit. Zones 1-4 have large emission sources, but the wind blows through the canyon enough to keep Zones 1-4 in compliance. They don’t regulate the emissions because they don’t have a problem. Zone 5, on the other hand, is screwed. All that pollution ends up at the end of the canyon in Zone 5, which has already ratcheted down on its sources as much as possible. Still, pollution from Zones 1-4 cause standards to be exceeded. Zone 4 is the nearest and the biggest contributor at 80% of the pollution, more even than Zone 5. Zone 1 contributes only a small portion, 1%, since it’s so far away. This scenario pretty well screws Zone 5, which is required to clamp down on emissions until it achieves compliance.
Under the Transportation Region approach, all zones in that canyon are now regulated with the same rules. This is great for Zone 5, which may now be able to meet air quality standards, but poor Zone 5, which contributed a small portion of the problem, is now just as regulated as Zone 5, where the impact is, and Zone 4, the biggest contributor. This scenario screws over Zone 1, which contributed only a small portion of Zone 5’s problem.