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Are Lead-Filled Clouds Altering Precipitation?

Get the Lead Out
We"ve all heard of lead balloons, but now there are also lead clouds ... and these lead clouds are going over about as well as lead balloons with scientists. The problem, as hydrologists and chemists see it, is that clouds pregnant with lead could change rain and snow patterns significantly. Lead is created by human sources, which drifts into the air, causing clouds to form more quickly and easily. And a cloud-covered world isn"t just dreary ... it"s yet another recipe for climate change.
•We know that the vast majority of lead in the atmosphere comes from man-made sources,• said atmospheric chemist Dan Cziczo of the Department of Energy's Pacific Northwest National Laboratory and study author.  •And now we show that the lead is changing the properties of clouds and therefore the balance of the sun's energy that affects our atmosphere.•
International researchers have shown for the first time a true connection between lead in the air and the formation of ice crystals that cultivate clouds.  The results reported in the May 2009 Nature Geoscience suggest that lead generated by human activities causes clouds to form at warmer temperatures and with less water.
A silver lining is that some of these clouds could let more of the earth's heat drift back into space, cooling the world somewhat.
When It Rains, It Pours
The main sources of atmospheric lead include coal burning, small airplanes flying at the altitude where clouds form, and construction or wind freeing lead from the ground. To find out how this lead affects clouds, the researchers collected air from mountain peaks around the world. They found that lead changed the conditions under which clouds appeared.  The air didn't have to be as cold or as heavy with water vapor if lead was present.
The computer simulation showed that high, thin clouds formed at lower altitudes and different locations in the northern hemisphere when lead was present in dust particles. This will likely change precipitation.
Clouds at lower altitudes let more of the earth's heat escape out to space. Lead-charged clouds could partly equalize global warming due to greenhouse gases.
But that doesn't mean lead in the atmosphere will simply cool the planet, according to Cziczo, since they looked at only one type of cloud.  Cloudy skies are far more intricate than they appear to the human eye.
•This work highlights how complex these interactions between lead and water vapor and temperature are,• said Cziczo. •They're not as simple as greenhouse gases.•
More research is necessary to look at the type of lead and how much is needed to influence clouds and rain or snow.

By Neil Whitehall
Get Hydrology Jobs, Contributing Editor


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