Dust from farming and other businesses in California is increasingly caught in national environmental regulators' spotlight these days. Respirable dust, smaller than four micrometers in diameter known as PM-4, reaches the alveolar region of the lungs, where it cannot be removed by the lungs' natural cleaning process. To understand more about how much dust is produced through agricultural operations, UC Davis researchers studied Central Valley farming practices, focusing on three crops, taking measurements at the source of the operations. Activities such as leveling the land before planting, plowing and cultivating, as well as harvesting, produced the highest concentrations of respirable dust at the farm implement as it is being used. Among harvest operations, corn produced the most dust, followed by tomatoes and wheat. Interestingly, organic operations actually produced more respirable dust than conventionally farmed land, note Michael J. Singer, a UC Davis professor of land, air and water resources, and Heike Clausnitzer, a postgraduate researcher working with Singer. This was the case, they say, because management of cover crops to improve the soil of the organically grown crops caused springtime operations to be done later in the season when the ground is far drier than it is during the winter and early spring months. Their research was published recently in California Agriculture.