Study: Surface Area of Floating Dust Important for Cloud Formation
May 25, 2016 | Atlanta, GA
Cloud droplets are more likely to form around insoluble particles floating in the atmosphere (e.g. dust, volcanic ash) when the particle surface is more “wrinkly” (with many pores, kinks, nooks and crannies), according to a new study.
Published in Scientific Reports, the study proposes a new method for determining the surface structure of these particles (a measurement known as the surface fractal dimension).
Led by Ari Laaksonen of the Finnish Meteorological Institute, the study was co-authored by Athanasios Nenes, a professor in Georgia Tech’s School of Chemical & Biomolecular Engineering and School of Earth & Atmospheric Sciences.
“We have been working for a number of years to come up with a unified theory of cloud formation,” Nenes says. “We’re trying to understand how particles act as seeds to make clouds. Without particles in the atmosphere, there would be no clouds formed in the sky.”
Cloud droplets form when water vapor in the atmosphere condenses onto tiny particles emitted from plants, human activity, dust, and other sources. For years, scientists believed that water-insoluble dust from deserts or volcanic ash would not serve as good nuclei for clouds unless soluble materials, like sea salt, were found in the particle. However, about five years ago, Nenes and his collaborators demonstrated that pure dust itself could serve as an effective cloud seed – even with the absence of soluble material.
In this new study, which shows that the surface structure (“wrinkliness”) of insoluble particles is an important determinant of cloud droplet formation, the researchers demonstrate an easier way to measure particles’ surface fractal dimension (D). Using a cloud chamber, in which clouds can be generated under controlled conditions, the researchers measured both the water vapor adsorption isotherm of particles and their ability to act as cloud condensation nuclei when introduced to humidified air in aerosol form.
This method compares favorably to previous techniques based on the measurement of nitrogen adsorption, which required a great deal more material, Nenes explains.
“It’s a breakthrough being able to get this type of information with a small amount of particle mass,” he says. “It paves the way for really novel work.”
The study, titled “Surface fractal dimension, water adsorption efficiency, and cloud nucleation activity of insoluble aerosol,” was co-authored by Jussi Malila, Hui-Ming Hung, and Jen-Ping Chen.