Organic molecules help larger water droplets form

Science News : Accurately predicting cloud formation is a difficult but important element of climate models. According to Kevin Wilson of Lawrence Berkeley National Laboratory and his colleagues, the current models have not been completely successful. Water droplets form when water vapor condenses onto airborne particulate matter called aerosols. Current models assume that water-soluble molecules alter the chemistry of the droplets, which allows them to grow larger. Wilson’s team tested that idea by filling a large tube with humid air and organic aerosols. Using lasers to measure the size of the water droplets that formed, the researchers found that the resulting droplets were 40% to 60% larger than expected if the organic molecules were simply dissolving. The scientists believe that a different mechanism is at work: Instead of dissolving, the organic molecules coat the exterior of the droplet, which lowers the surface tension of the water and makes it easier for additional water to condense and join the droplet.