LOS ANGELES, May 3 (Xinhua) -- Air pollution causes 5,400 premature deaths annually in Southern California, it was reported on Thursday.

    Locomotives are responsible for more than 32 tons per day of pollutants, an amount equal to that produced by 1.4 million cars, said the Los Angeles Times, quoting the South Coast Air Quality Management District (AQMD).

    State and regional agencies have found that the sooty particulates put out by trains are particularly harmful, according to The Times.

    AQMD officials last year passed three regulations, requiring railroads to shut down idling locomotives or obey other local laws designed to clean up deadly diesel pollution.

    The regulations asserted AQMD's authority to regulate emissions under the federal Clean Air Act and state policing laws, The Times reported.

    But two railroads and a trade group filed suit, saying that under special exemptions passed by Congress more than a century ago, they do not have to abide by local laws that could interfere with interstate commerce.

    A federal judge has ruled that Southern California air regulators cannot require railroads to shut down idling locomotives or obey other local laws designed to clean up deadly diesel pollution, said the paper.

    The decision invalidates action taken last year by the AQMD to reduce a major source of air pollution in the Southland, said the paper.

    Officials at Burlington Northern Santa Fe Railway and Union Pacific said they are spending billions to replace older, dirtier equipment, and have voluntarily cut idling times, The Times reported.

    U.S. District Judge John F. Walter, based in Los Angeles, acknowledged the region's dismal air quality but nevertheless ruled Tuesday in favor of the railroads.