February 5, 2013
Certain Volatile Gases Found To Promote Cloud Formation
April Flowers for redOrbit.com - Your Universe Online
A new study from Columbia Engineering and the Georgia Institute of Technology shows — for the first time — certain volatile organic gases can promote cloud formation in ways atmospheric scientists have never before considered.The findings of this study were published online in the Early Edition of the Proceedings of the National Academy of Sciences (PNAS).
"This is the first time gases have been shown to affect cloud formation in this way," says V. Faye McNeill, associate professor in Chemical Engineering at Columbia University's Fu Foundation School for Engineering and Applied Science. "This is a very exciting finding that will improve our ability to model cloud formation, an important component of climate."
Because clouds have such a significant influence over our climate, the team has been focused on understanding the impacts of aerosols, or airborne particulate matter, on cloud formation.
"Low-level clouds cool the planet by reflecting incoming sunlight back to space, so anything that perturbs them can have a major impact on our climate," Athanasios Nenes, professor & Georgia Power Faculty Scholar at the Georgia Institute of Technology, explains in a statement. Pollution produced by humans release many airborne particles into the atmosphere. These act as seeds for cloud droplets, meaning that clouds forming in polluted air masses are likely to be more reflective then their "clean" counterparts.
"Our study," Nenes says, "shows that certain gas phase compounds tend to stick on particles, making them 'soapier' and promoting their ability to form cloud droplets. This mechanism has not been considered in climate models before."
When water vapor condenses on particulates called cloud condensation nuclei (CCN), clouds form. Cloud properties can be profoundly impacted by variations in CCN concentrations, which can have effects on both regional and global climate. A significant percentage of aerosol mass in the troposphere - the lowest level of the Earth's atmosphere - is made up of organic matter, which can profoundly influence the activity and concentration of CCN and cloud droplets.
According to the study findings, two ubiquitous atmospheric trace gases, methylglyoxal and acetaldehyde, can enhance aerosol CCN activity. This is true even if they do not contribute any detectable organic mass when taken up by aerosol particles. The team generated aerosol particles and exposed them to the surfactant gases methylglyoxal and/or acetaldehyde in the lab's aerosol reaction chamber for up to five hours. Using a cloud chamber co-invented by Nenes and his group, the exposed particles were then tested for their ability to form cloud droplets.
The results showed the gas-phase surfactants may enhance the activity of atmospheric CCN, so "volatile organics in the atmosphere may act as a reservoir of surfactants that can be taken up by aerosol particles and augment their CCN activity."
Both groups plan to continue the study, doing more experimental work with other organic gases under a variety of conditions.
McNeill and Nenes say this will "help us understand how general this newly discovered phenomenon is, and, most importantly, will enable us to incorporate it into models of cloud formation so we can improve the predictive power of climate models."
"The effects of aerosols on clouds is one of the greatest sources of uncertainty in our understanding of climate," adds McNeill, "so it's fun to work on a problem that is both important and intellectually fascinating."