Raining oil in Louisiana? Not likely.
Raining oil in Louisiana? Oil on the ground, very likely. Raining oil, no.
A YouTube video has been making the rounds purporting to show evidence of oil that has "rained" from the skies over the New Orleans suburb of River Ridge.
The far more likely source is closer to Earth – runoff from roads, parking lots, and industrial facilities in the area where the video clip was filmed.
IN PICTURES: Gulf oil spill response
"There's certainly a lot of reasons to be concerned" about the Deepwater Horizon blow-out, says Doug Helton, the National Oceanic and Atmospheric Administration's incident response coordinator with long experience dealing with urban oil runoff. "This is not one of them."
The reasons have to do with nature of oil and how its components behave in the atmosphere, scientists say.
In short, oil and water don't mix, explains Christopher Marshall, a former research chemist with Amoco Oil and now director of an institute looking for ways to develop biofuel replacements for oil and gasoline at the Argonne National Laboratory in Argonne, Ill.
The story begins with the oil itself, he says. Oil consists of four broad categories of hydrocarbons: paraffins, napthenes, aromatics, and asphaltenes. The relative amount of each depends on the age of the oil deposit. Older oil is heavy on the heavy hydrocarbons, such as asphaltenes -- the basic material for patching potholes, Dr. Marshall says. Younger oil, such as the Gulf reservoir BP was trying to exploit, is dominated by the other, lighter hydrocabons.
When the leaking oil reaches the surface, the lightest hydrocarbons in the blend evaporate, giving off gases such as methane, ethane, and propane. This evaporation turns the remainder of the oil into a heavier globs that become the tar balls washing on to beaches or oil that loses its buoyancy compared with water and sinks into the water column.
The evaporating hydrocarbons can contribute pollution problems of their own, combining with ozone to form smog, for instance. But they don't recombine to form oil that can subsequently return as a component of rain drops.
One theoretical pathway for oil itself to get lofted involves waterspouts – essentially small tornadoes over the ocean. Indeed, local residents spotted and photographed a water spout over Lake Ponchartrain earlier this month.
While oil from the BP blow-out hasn't reached the lake, it has long had pollution problems of its own.
Still, that mechanism is a stretch, researchers acknowledge.
But the video is not without its own take-home message, Mr. Helton adds.
"What we're really looking at is a non-point source of oil pollution, which is a very big thing to be concerned about," he says. Oil leaking from cars to lawnmowers or oil that's not properly disposed of "adds up to be a lot of oil every year that comes into rivers and bays and ultimately out into the ocean."
IN PICTURES: Gulf oil spill response
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