The risk of developing cancer from air pollution in Southern California has decreased in recent years, but people living near the ports and along transportation corridors still face a high risk, a two-year study revealed Friday.

In the new study, researchers analyzed air quality samples at 15 sites across the region starting from April 2004 to March 2006. There were collected a total of 18,000 samples and analyzed for 33 of the most harmful airborne carcinogens known, according to South Coast Air Quality Management District’s spokesperson, Sam Atwood.

The findings showed that the highest concentration of airborne carcinogens centered on San Pedro Bay, downtown Los Angeles, Fontana and Burbank. The number of people living in these areas rises to 16 million people.

According to researchers, diesel exhaust carries most of the risk, counting for 84 percent of the region’s cancer risk. However they also analyzed other toxic elements like lead, benzene, arsenic and formaldehyde.

"Diesel exhaust is the No. 1 public enemy. We clearly have not adequately controlled diesel emissions in this region," said Barry Wallerstein, executive officer of the South Coast Air Quality Management District, which conducted the study.

The cancer risk from air pollution is down to 15 percent when compared to a similar study completed in 1999. However, the good news was immediately shadowed by the fact that the region still has the dirtiest air in the country.

"While we see some improvements, the remaining risk level is way too high," said Wallerstein.

Overall, for every 1 million people, 1,200 develop cancer during their lifetime as a result of exposure to dangerous chemicals in the air, the study estimated. A lifetime was estimated to be 70 years.

The number is a little higher in Fontana, rising to 1,400. Moreover, the study revealed that the number rose to 2,900 per million for those living around the ports of Los Angeles and Long Beach, where diesel use is significant. The area with the lowest cancer risk was Anaheim.

"This reduction in cancer risk shows that we are on the right track in tackling toxic air pollution. However, the remaining cancer risk is completely unacceptable. Thousands of residents are getting sick and dying from toxic air pollution. Some of them live in low-income, minority neighborhoods that may be heavily impacted by cancer-causing air pollution," said William Burke, chairman of the South Coast Air Quality Management District board, which released the report.

The members of the board expressed their will to work more closely with the California Air Resources Board and join a state lawsuit against the federal government that would create the country’s first greenhouse gas limits on cars, trucks and SUVs.

The board will ask for public comments on the study for 90 days and an update will be prepared based on these comments. The plan will be presented this summer.

"There's tremendous work to do still," Burke said.