Coal is our most abundant fossil fuels. The
But coal is not a perfect fuel.
Trapped ins
ide coal are traces of impurities such as sulfur and nitrogen. When coal burns, these impurities are released into the air.
While floating in the air, these substances combined with water vapor (for example, in clouds) and form droplets that fall to earth as weak forms of sulfuric and nitric acid –
scientists call it "acid rain".
There are also small patches of minerals - including common dirt - mixed in coal. These tiny particles do not burn, and make up the ashes back in a coal combustor. Some of the tiny particles also get caught in the swirling combustion gases and, together with water vapor, form the smoke coming out of a coal plant's chimney. Some of these particles are so small that 30 of the side-by-side would barely equal the width of a human hair!
Also, coal like all fossil fuels is formed out of carbon. All living things - including humans - are made of carbon. (Remember - coal started out as living plants.) But when coal burns, its carbon combines with oxygen in the air and produces carbon dioxide. Carbon dioxide is a colorless, odorless gas, but the atmosphere is one of several gases that can trap the earth's heat. Many researchers believe that this is causing the earth's temperature to rise, and this warming could alter Earth's climate (read more about the "greenhouse effect").
Sounds like coal is a dirty fuel to burn. Many years ago, it was. But things have changed. Especially in the last 20 years, researchers have developed ways to capture the pollutants trapped in coal before the impurities can escape into the atmosphere. Today we have technology that can filter out 99 percent of tiny particles and remove more than 95 percent of acid rain polluting coal.
We also have new technologies that will reduce carbon dioxide emissions from burning coal more efficiently.
Many of these technologies belong to a family of energy systems called "clean coal technology." Since the mid-1980s,
