We have many approaches that can be used to lessen air pollution, including a variety of technologies and regulatory policies.
One technological approach is a smokestack scrubber, which captures harmful pollutants before they leave the smokestack. One type of scrubber removes sulfur dioxide from the emissions of coal-fired power plants.
In this process, the emissions from burning coal enter the smokestack and start to rise.
A mist of powdered limestone and water traps the pollutants. The limestone binds to sulfur dioxide, sinking with it to the bottom of the scrubber.
As the emissions flow through the scrubber, they become cleaner until clean air is finally released.
The dirty water resulting from this process flows away. The contaminants are removed, and the water is used again.
If a producer implements changes that reduce pollution emissions below their total credit, they can sell their leftover credits to another producer who exceeds their allotment.
Over time, pollution levels can be reduced as the cap—or limit—is lowered. A downside to cap-and-trade plans is that pollution can become concentrated in areas where industries choose to buy additional permits rather than reduce emissions.