Among the pollutants darkening the sky in California's San Joaquin Valley are tiny dust particles known as PM-10. Harvesting and other agricultural activities, as well as road dust, contribute to the PM-10 emissions. To help reduce future PM-10 levels in the Central Valley and elsewhere, researchers at UC Davis' Crocker Nuclear Laboratory and the campus's land, air and water resources department are conducting a $400,000 study to look at how various factors such as soil type, humidity, wind speed and leaf canopies alter such dust emissions. The study, funded by the U.S. Department of Agriculture and commodity groups, will involve field sampling and lab experiments, including the use of a box designed to suspend particles in air to obtain samples based on their aerodynamic properties. The researchers aim to develop a model to predict major dust sources in the valley. The study continues UC Davis research begun in 1991, when researchers measured and analyzed dust emissions from specific agricultural practices and dirt roads in the valley.