Los Angeles, wedged between the ocean to its west and mountains to its east, is built for air pollution. Contaminants from cars, utilities and factories pump out particles and gases that enshroud the city in smog.

California became the first state to regulate air pollution when then-Governor Ronald Reagan signed the Air Resources Act in 1967. The U.S. caught up with California three years later when another California Republican, President Richard Nixon, signed the Clean Air Act.

California maintains its role as an environmental law laboratory. This fall it will introduce a statewide cap-and-trade program to gradually reduce its climate pollution.

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