Today, a major decision was handed down by the U. S. Court of Appeals for the District of Columbia Circuit. The short version is that a EPA (Bush II era) rule which prevents states and localities from requiring air polluters to monitor their emissions was struck down.
First, it's important to understand the significance of the U. S. Court of Appeals for the District of Columbia Circuit. Our country's judicial system has three levels. The first is the trial level. This is the kind of court that initially deals with any offense, from a traffic violation to murder. It's equivalent to what you see on Law & Order. The second level is the appellate (appeals) level, which itself has multiple sub-levels. Essentially, when you hear about a case being appealed, these are the courts that happens in. The third level is the Supreme Court, which you're likely familiar with already. The U. S. Court of Appeals for the District of Columbia Circuit is in the appellate level. Appellate courts are regionalized geographically (each region referred to as a circuit) and they hear appeals from courts in their region. The reason this particular court of appeals is so significant is that it hears cases for the District of Columbia (Washington, D. C.) circuit, and thus hears appeals in court cases involving any government agency based in the Capital, which includes the EPA. For this reason, it's known colloquially as the second highest court in the land. It also pays to be aware of the decisions handed down by the three judges whom sit on this court, as it's one of the first places Presidents look for Supreme Court Justices.
The Clean Air Act was passed in 1963 and has been amended and extended numerous times since. The applicable power within the CAA is to set emission limits for air pollution from stationary sources (like a smokestack at a coal plant) and to measure compliance with those emission limits. However, until recently, the regulations were pretty mazelike and it wasn't simple for a factory owner to determine what limits were applicable to him. In 1990, Congress passed a batch of amendments including Title V of the act, which set up a system requiring polluters to apply for specific emission permits including emission limits and monitoring requirements.
Now that Congress has passed the CAA, the ball gets passed to the EPA which has to enforce the Act. A problem arose in ensuring the monitoring requirements would actually be adequate to enforce compliance with emission limits. For example, what if the relevant statute requires annual monitoring of emissions, but the emission limit is expressed in units per day? Dividing the annual output by 365 (or 366 in a leap year) isn't sufficient as you can't tell if emission limits were violated on any particular days. Factory owners like this because you can't tell if they ever exceeded their daily limit. Unless a factory is open every day of the year (depends on what it does), this means polluting daily to its limit a factory will fall far short of its annual limit (daily limit × 365).
To solve this problem, individual states (mainly California) began to required plants to install more stringent monitoring equipment to ensure plants were complying with EPA regulations. Industry organizations absolutely hated this and lobbied from 2002 until 2006 for this to be made illegal, and in 2006 the EPA banned this practice. That's the decision that was overturned today.
Let's review how this works within our government's system of checks and balances. Congress passed the Clean Air Act (the legislative branch passes laws) and the EPA is responsible for enforcing it (executive branch enforces the laws). In this case, the question was whether or not the EPA's 2006 ruling violated the CAA (appellate courts address questions like this, and this is what the U. S. Court of Appeals for the District of Columbia Circuit often deals with). In the end, it found the EPA's 2006 ruling violated the CAA and it was struck down, so now states and localities can once again require more stringent monitoring of polluters. The way the legal system works, this decision can only be overturned by the Supreme Court (no way that's going to happen). The Supreme Court would have to either determine the case was fundamentally flawed in some way (it wasn't) or that the CAA is unconstitutional (which would a political bombshell on scale with Iran launching nukes at Israel).
Score one for the good guys.
Text of the Decision (.pdf)