Particulate matter consists of very small liquid and solid particles from a variety of human and natural sources. When inhaled, fine particles can be particularly harmful to children, active adults, and the elderly. Particulate matter also deposits in the lake and results in reduced clarity. Ambient concentrations of PM2.5 and PM10 are generally low in Tahoe and are not a human health concern. Wildfires inside and outside can cause PM concentrations to increase to levels of concern for human health. Sources of fine particulate matter in the Tahoe Basin include resuspended road dust, wildfires, prescribed burning, wood burning (residential and campfires). Regional programs such as increased sweeping, old wood stove replacement, and forest fuels project to prevent wildfire aim to reduce particulate matter.