3. Los Angeles
3. Los Angeles
Population: 17,877,006
Cardiovascular cases: 4,109,426
Rank in most ozone-polluted cities: 1

One of Los Angeles' biggest pollution problems is its ports.

"Forty-three percent of all the imports in the country come through here," said Sam Atwood, spokesman for the South Coast Air Quality Management District. "Once the cargo comes in, it gets put on a truck, moved to warehouses and taken to trains. Almost everything is powered by diesel."

There have been several efforts made to cut back on this diesel-related pollution. One is the voluntary slowing of ships as they come into port, starting from about 24 nautical miles out. By doing so, the ships burn less fuel and produce lower emissions.

The port is also upgrading facilities so ships can plug into electricity from shore and rely less on running their auxiliary engines.

The state is also dealing with pollution on the road by imposing strict gasoline regulations that cut toxic chemicals like benzene.

"When I first flew out here in 1987 to interview for a job, I almost had a panic attack," said Atwood. "I was 10 miles from the mountains and I couldn't see them. That doesn't happen anymore."

By Les Christie @CNNMoney - Last updated April 25 2012: 12:12 PM ET
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