Air pollution is caused by contaminants such as smoke and car exhaust. In cities, a hazy combination of gases and soot causes "smog".
Intensive lobbying by Kyoto Protocol supporters got the Supreme Court to classify carbon dioxide as a "pollutant" so it would come under EPA control (see greenhouse gases).
Reagan said: "Approximately 80 percent of our air pollution stems from hydrocarbons released by vegetation." [1] This was morphed into Trees cause pollution in campaign literature and used to imply the Reagan was dishonest or unintelligent, even though (as scientists have said) he was correct.[1]