Unpolluted rainfall is slightly acidic, with a natural pH of about 5, due to naturally occurring constituents of the atmosphere, such as carbon dioxide, but acid rain has a pH of about 4. ... Since passage (1970) of the Clean Air Act, U.S. emissions of sulfur dioxide have been reduced substantially, due to the burning of low-sulfur oil and coal, installation of costly scrubbers in smokestacks (see smoke) and electric plants, use of pollution controls by metal processors, reduction of diesel-fuel sulfur contents, and the installation of catalytic converters to clean automobile exhausts. ...

• Word Count: 632
• Approx Pages: 3
• Grade Level: Undergraduate