Aerosols Brighten Clouds

It was suggested 25 years ago that industrial aerosols promote cloud formation, thereby increasing the Earth's albedo and cooling it. Now a research team at Brookhaven National Laboratory in Upton, N.Y., and at Purdue University in West Lafayette, Ind., has confirmed the brightening effect of sulfates on clouds over the North Atlantic.

The group compared a model that forecasts the mixing of sulfate and SO₂ with visible and mid-infrared radiance measurements of low-level clouds from the NOAA-9 satellite in April 1987. For a given amount of water in a cloud, the presence of the aerosol led to higher reflectivity.

Although aerosols on a global scale might offset the warming influence of greenhouse gases, their distribution is inhomogeneous and concentrated in the industrialized Northern Hemisphere. The researchers suggest that the study, which appeared in the Feb. 19 issue of Proceedings of the National Academy of Sciences, points to the development of more accurate, measurement-based models of the effects of the pollutants.