Occasionally at 6 a.m. black smoke rises south of LAX. At first I thought a plane had crashed, but I’ve seen the plume several more times. After a few minutes, it dissipates. What is it?

    The black blast is from a giant smokestack at a Chevron refinery in El Segundo, a mile south of the airport, which makes jet fuel, diesel fuel, and gasoline. During maintenance—or if, say, a pump fails—the processing system shuts down, and pressurized hydrocarbons shoot 100 feet up the stack, where a pilot light ignites them. Early in the burn, the materials create those clouds of soot you’ve spotted dirtying the atmosphere. (Chevron calls it “clean burning.”) “It’s like lighting a barbecue,” says spokesman Rod Spackman. A really, really big barbecue.
    Photograph courtesy flickr/cote