The threshold standards for “visibility” were established to protect the unique aesthetic scenic values of the Tahoe Region. Visibility measures the distance at which an object or light can be clearly discerned by the human eye. Sources of locally generated haze pollutants include entrained/suspended roadway particles, vehicle emissions, residential wood burning, campfires, prescribed fires, and wildfires. Increasingly, particles responsible for the degradation of regional visibility in the Tahoe Basin include dust and other pollutants transported into the Basin from areas as far as Asia, and record-setting catastrophic wildfires throughout California and the western states in the last five years. Regional programs such as decreasing the number of polluting wood stoves and work to improve forest health aim to increase regional visibility.