In 2015 the US Supreme Court (SCOTUS) rejected the Obama era EPA mercury emissions rule changes because the EPA didn't balance the cost of the rule with the ben

In 2015 the US Supreme Court (SCOTUS) rejected the Obama era EPA mercury emissions rule changes because the EPA didn't balance the cost of the rule with the benefit. The economic benefit of the reduction in mercury was about $6 million at a cost of $9-10 billion. The SCOTUS rejected the rule changes because the benefit didn't appear to justify the cost as required by statute. It sounds like this balancing is part of the rule-making requirements for the EPA. So, the EPA went back and included numerous so-called co-benefits into its accounting, mostly related to reduced particulates. The new analysis increased the economic benefit of the mercury reduction such that it significantly out-weighed the cost. This brought the mercury reduction rule into compliance with the SCOTUS decision. The problem is that the EPA used the economic benefit of particulate reduction to justify a mercury reduction. Why not just make a rule to reduce particulate emission? That is where the real benefits were coming from not the mercury reduction. Probably because the EPA doesn't have the power to regulate particulates as they do mercury emissions, or something like that. Meaning the EPA would have to go to congress to get the authority to either regulate particulates directly or excuse mercury emission regulations from the cost-benefit analysis requirements. Also, probably because mercury emission regulation particularly impacts the coal industry. Whereas, a generalized particulate emission rule would affect many other industries making it politically problematic.