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Clouds and Pollution -- a Climate Change Mystery Solved

By By Stephanie Paige Ogburn, E&E reporter
February 20, 2013, 5:53:24 AM EST

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How does pollution affect cloud formation and climate change? This question has long been an unsolved mystery of climate science, leading to uncertainty in climate modeling. Research published this week in the Proceedings of the National Academy of Sciences takes a big step toward answering that question and helping scientists improve those models.


For nearly half a century, scientists speculated that air pollution from burning fossil fuels causes clouds to form differently. Clouds are made up of many small water droplets that form around particles in the atmosphere; when those droplets tried to form around oily particles, scientists believed they would form more slowly, since "oil doesn't mix with water," explained Athanasios Nenes, the Georgia Institute of Technology professor who led the study.

Surprisingly, Nenes found, this just isn't true. In a set of experiments that took place across the globe, Nenes tested cloud formation and discovered that droplets form just as quickly around pollution particles as they do around other particles.

"Which is pretty remarkable, but that is what we found, and we went pretty much everywhere we could get our instruments to," Nenes said.

To figure out how pollution actually affected cloud formation, Nenes and his team flew an aircraft equipped with a miniature cloud formation chamber -- essentially a moist tube that is heated on one end and cooled on the other -- in 10 different cloud-forming environments.

An airborne connection

They flew over the Arctic, through smoke from forest fires and above the 2010 Deepwater Horizon oil spill in the Gulf of Mexico. Yet even when they flew the cloud chamber through the incredibly oily particles above the Gulf of Mexico, Nenes said, droplets formed at the same rate as in nonpolluted environments.

Because clouds regulate how much sunlight can get to the Earth and can also trap heat in the atmosphere, they have a big effect on climate. Better knowledge on how they form can help climate models become more accurate. Nenes was pleased with his study results because they simplify what was once a big uncertainty in the models.

"It's something that we weren't expecting to see, but it's actually a good thing because it makes the models easier," Nenes said.

Charles Kolb, an atmospheric chemist who has also researched how pollution affects cloud formation, said the study provided real-world results that closely matched recent laboratory experiments on pollution and cloud formation.

"It's very important to have a connection between the laboratory science and the actual science in the real world. And [this] paper showed the two are very closely related," he said.

Reprinted from ClimateWire with permission from Environment & Energy Publishing, LLC. 202-628-6500. E&E Publishing is the leading source for comprehensive, daily coverage of environmental and energy issues. Click here to start a free trial to E&E's information services.

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