An international team of researchers says it has discovered a new atmospheric compound that reacts with sulfur dioxide to form sulfuric acid, which produces acid rain, has negative respiratory effects on humans, and causes increased cloud formation. Reporting in Nature, the scientists from the U.S., Finland, and Germany identified the new compound as a type of carbonyl oxide, formed by the reaction of ozone with natural and manmade hydrocarbons, known as alkenes. When the carbonyl oxide compounds react with sulfur dioxide — which is primarily produced by coal and other fossil fuel combustion at power plants — large amounts of sulfuric acid are produced. The scientists say it is the first time that this complex new interaction of atmospheric compounds has been documented. Sulfuric acid creates acid rain that is harmful to terrestrial and aquatic life, and airborne sulfuric acid particles play the main role in the formation of clouds, an increase of which could help cool the planet. Smaller sulfuric acid particles near the planet’s surface have been shown to cause human respiratory ailments.