China is particularly struggling to curb what are known as secondary pollutants, formed when primary pollutants such as emitted sulfur dioxide and nitrogen oxides, from coal burning and other sources undergo reactions in the atmosphere.

WSJ: China's Pollution Fight Faces Resistance

Chastened, in 1995 Ertel joined the then-new pollution desk at Natsource, where he sold sulfur dioxide credits in a market created by tough U.S. regulations on coal-burning utilities.

FORBES: Selling the Blue Sky

Chastened, in 1995 Ertel joined the then new pollution desk at Natsource, where he sold sulfur dioxide credits in a market created by tough U.S. regulations on coal-burning utilities.

FORBES: Magazine Article

Fuel cells offer several advantages: they do not have moving parts and there is no burning involved, so there are negligible emissions of environmentally harmful gases like nitrogen, sulfur oxide and carbon monoxide.

FORBES: Magazine Article