Clouds can hold in heat emitted from the Earth's surface, contributing to climate warming. But they can also reflect incoming sunlight back to space, producing a climate cooling effect. Predicting how cloud cover will change in the future is therefore essential to good climate modeling.
"The reason we care about droplet formation rates is because the more slowly the droplets form, the more droplets you end up having in clouds," Nenes said. "This, in turn, affects cloud properties and their climate impacts. For many years, there was the perception that having a lot of oily organic compounds from pollution would make water uptake a lot slower and might make droplets take longer to form. If that were true, it would mean that the impact pollution could have on clouds and climate would be much larger than we thought."
And that created a large question mark in climate models.
To address that issue, Nenes and his collaborators began a series of studies using a mini cloud formation chamber small enough to be operated aboard an aircraft. The chamber consists of a long metal tube that is heated at one end and cooled at the other. The walls of the chamber are kept moist, and air containing particles from outside the aircraft is flowed through. Droplets form on the particles when air in the chamber becomes cool enough that it can no longer retain the moisture. The droplets then exit the chamber where they can be studied.
"With the chamber, we essentially create a cloud in a tube," Nenes said. "The difference between the cloud in the tube and the cloud outside is that the tube allows us to precisely control the temperature and the amount of water vapor available. We know ex
|Contact: John Toon|
Georgia Institute of Technology