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LOS ANGELES (CNS) - Levels of hazardous pollutants generated by planes  at Los Angeles International Airport are more dangerous than previously  believed, spreading pollution over a much wider area than previously believed,  according to a USC study released today.

``Our research shows that airport impacts extend more than five times  further that previously assumed,'' according to Scott Fruin, lead researcher  and assistant professor of preventive medicine at the Keck School of Medicine  at USC. ``Effects from planes that are landing appear to play a major role in  this large area of impact.''

According to the study, published in the journal Environmental Science  and Technology, high concentrations of ultrafine particles extended east more  than 10 miles downwind of the airport boundary and across a roughly 20-square- mile area, including Lennox, Westmont, South Los Angeles, Hawthorne and  Inglewood. The pollution in some instances -- depending on wind conditions --  also stretched into areas south of the airport.

The findings were contrary to earlier beliefs that air pollution  dissipated quickly after airplane takeoffs, with pollutant dissipating rapidly  downwind.

Researchers from USC's Keck School of Medicine conducted the analysis  over 29 days. They found chemical concentrations to be up to two times higher  than background pollution levels within 20 miles of the airport, compared to  areas outside that zone. Concentrations four times higher than background  levels extended for a distance of six miles.

``Given the existing concern about the possible health effects of urban  ultrafine particle levels, living in an area with two to four times the average  L.A. levels of ultrafine particles is of high public health concern,'' said  Neelakshi Hudda, research associate in preventive medicine at the Keck School.

Officials with Los Angeles World Airports, the city agency that operates  LAX, said they have not had a chance to review the study, but said a multi- year study released by the airport in January found that all major pollutants  were below national standards, and that air-pollution concentrations showed  sharp decreases farther from the airport.

"LAWA cannot directly control aircraft-related emissions,'' according  to the agency. ``But, LAWA has taken steps to reduce emissions that are within  our responsibility and influence."

LAWA officials noted that all gates at LAX are fitted with electrical  connections so planes can shut down their aircraft engines, reducing ground  emissions. They also noted that the airport uses electric ground-handling  service vehicles for aircraft towing, baggage and other services.