Thinking More About Oily Rain

It's easy to pooh-pooh the idea of oily rain. Indeed these folks have several rubbish ideas why oily rain can't exist, or is unlikely:

Because oil generally doesn't evaporate, it shouldn't be possible, under normal circumstances, for it to rain down from the skies. But Charlie Paxton of the National Weather Service tells WTSP in Tampa that "a water spout could pick up some oil and carry it a short distance."

Another possibility is that the dispersant BP has been using to thin the oil, Corexit, may have made some of it light enough to be absorbed in the atmosphere.

This skeptical article at Fast Company declares it "not likely" that it's raining oil, but it quotes the EU Times as stating that "when combined with the heating Gulf of Mexico waters, [Corexit's] molecules will be able to 'phase transition' from their present liquid to a gaseous state allowing them to be absorbed into clouds and allowing their release as toxic rain upon all of Eastern North America."

And the article also points to a report (PDF) from the newly-renamed federal Minerals Management Service which states that oil, if it's light enough, has been known to evaporate. "So it might be possible that oil is mixing with rain," Fast Company's Ariel Schwartz concedes.

"Worst case scenario? It's petroleum mixed with Corexit, the cancer-causing dispersant BP's spraying on its oil slick," writes ben Wojdyla at Jalopnik. "Best case scenario? Dirty roads."

Well, I'm not persuaded....

One thing we do know about oil is that it's hydrocarbons include lighter-molecular-weight compounds that evaporate readily. And those big oil slicks are out there in the Gulf of Mexico, waiting and baking in the sun.

So what happens to those evaporated compounds?

In the normal course of events, lots of aerosol particles will nucleate from the vapors as a result of oxidation, and photochemical reactions, due to exposure to sunlight.

Nevertheless, these particles should still be hydrophobic for the most part, shouldn't they? Only if they are pure compounds, which they are unlikely to be in a semitropical marine environment. Lots of sea salt, and other soluble salts, could combine with the products of hydrocarbon oxidation to form mixed aerosols. A typical mixed aerosol particle could be partly hydrophobic and partly hydrophilic.

Could these mixed aerosol particles function as condensation nuclei? Maybe - particularly if strong updrafts in powerful thunderstorms deplete the population of nuclei best suited for condensation nuclei and start drawing upon this mixed population. Even though oil products will resist incorporation into rain, sometimes mightily, it's not an absolute resistance. Whether through nucleation scavenging or precipitation scavenging, routes should exist to bring even the most hydrophobic compounds into rain! And you don't need much oil, or oil byproduct, to place a sheen on water!

Let's get those relief wells dug! ASAP!