[Dr. Scott W. Tinker] You just heard me say coal is dirty, but you might have heard politicians or television commercials talking about clean coal technology. What's going on? They're suggesting removing CO2 from the emission stream to make coal clean. There are a few pilot projects to add units onto existing coal plants to capture carbon, and there are technologies proposed to turn coal into gas separating the CO2 before it is burned. But both of these are too experimental and expensive to roll out at the huge commercial scales necessary to make a difference today. There are, however, technologies to reduce particulates and other pollutants produced by burning coal. What's called the bag house, like rows of giant vacuum cleaner bags, can remove all the ash and some of the heavy metals. Scrubbers and catalysts capture sulfur oxides, nitrogen oxides, and some of the mercury. The best coal plants capture these emissions, but worldwide more of them don't. Why? Because adding these processes is complicated and expensive, and that takes away some of the biggest benefits of coal: simplicity and affordability. And it takes energy to run all these processes, and that comes from the coal plant itself. Which means to produce the same amount electricity, the plant has to burn more coal, and that produces more pollutants and more CO2. So we can clean up particulates and other pollutants from coal plants, but with greater cost, complexity, and carbon emissions.