Southeast resistant to global warming.

• Position: Smoky Mountains

Many photographs of the Smoky Mountains show layers of tall hills, shading to purples and grays in the distance. Tiny particles in the atmosphere help create the effect, which makes for stunning pictures, but human-caused enhancements of those fine particles also contribute to poor air quality in the southeastern U.S., and may help explain why the region has not warmed like the rest of the nation.

Scientists from the Cooperative Institute for Research in Environmental Sciences (CIRES) at the University of Colorado, Boulder; the National Oceanic and Atmospheric Administration, Upton, N.Y.; and colleagues from dozens of other institutions are taking one of the most detailed looks ever at the natural and man-made emissions that affect air quality in the Southeast, as well as their movement and chemical transformations within the atmosphere.

The mission, called Southeast Nexus, should help scientists determine the origin of the fine particles and how they contribute to the haziness in the region and affect regional air quality and temperature trends. Both the natural environment and human activities contribute to haziness. Plants and trees give off gases called volatile organic compounds that can react with man-made emissions in the atmosphere to create pollutants such as ozone and the tiny particles known as aerosols--the building blocks of haze.

Power plants, refineries, and other industrial sources also give off gases that lead to haze formation. Aerosols not only diminish air...