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Carbon in the Air Encourages Cloud Formation

By making their own clouds, scientists have figured out how some of the fattest water droplets form. And, they find, it’s what’s on the outside that matters.

Climate scientists need to understand how water droplets assemble into colossal clouds. That’s the only way they can reproduce cloud formation in the computer programs that they use to model climate change. Right now, that’s something that these computer models struggle with.

“A cloud model needs to capture the underlying chemistry correctly,” says Kevin Wilson. “It appears that the current one does not.”

Wilson is a physical chemist at Lawrence Berkeley National Laboratory in California. He was part of a team that did the new research. Tiny, carbon-containing molecules can coat the outside of a developing droplet, helping it grow. In fact, they showed, these carbon-based molecules can lead to droplets that are 50 percent wider than had been expected.

The water droplets are bigger because the carbon-containing (or organic) molecules decrease the water’s surface tension. That allows more water molecules to condense out of the air, latching onto the droplet. And larger water droplets are more likely to form clouds, Wilson notes.

His team’s findings appear in the March 25 Science.

Maria Di

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