Smoke and Fire
Smoke can be present in the park during any month. Smoke may be localized to small topographical regions of the park or may be regional and quite dispersed, depending on the number of fires, fire size, and local/regional weather patterns. See a map of regional smoke impacts and current air quality values at various sensors throughout the park.
Wildfire season spans the hottest, driest months of the year and continues until fall rains arrive, making smoke commonly present in the park between July and November. Fire and smoke may also occur in the park during cooler, wetter months when fire managers can safely use fire on a small scale to manage forest health. Yosemite fire managers may prescribe burns on small tracts of land, or burn consolidated piles of excess fuels. These smoke events are usually short term with local air quality impacts. They are carefully planned and monitored to manage smoke impacts.
Yosemite National Park is a fire-adapted ecosystem. The animals and plants of the park have evolved alongside naturally occurring seasonal fires. Fires promote biodiversity, variable habitat, and forest resiliency. Native Americans in Yosemite regularly set fires to encourage growth of plants useful to them and to clear the ground beneath oaks for easier acorn gathering. Because of fire’s beneficial effects on the ecosystem, it is important to let wildfires burn when responsible and feasible. Yosemite’s fire managers aim to minimize impacts of smoke on public health while maximizing benefits of fire to forest resources. Visit Yosemite Fire News for up-to-date information on fire in the park.
Smoke and Air Quality
Smoke is a mixture of gases and fine particles. These particles can be directly emitted from fire, or can secondarily form in the atmosphere as gasses react. Some particulate matter is large, such as ash, but much of it is very fine and cannot be seen with the naked eye. To monitor smoke’s impact on air quality, Yosemite measures the concentrations of very small particulate matter. Fine particulate matter impedes vistas in the park, reducing visibility below the standard distance of 150 miles.
Fine particulates also present the primary health concern from smoke. The smaller the particle, the greater the potential for causing health problems. Particulate matter smaller than 2.5 micrometers (PM2.5) is 30 times smaller than a human hair, and can penetrate deep into the lungs, causing acute and chronic respiratory and cardiovascular problems. Yosemite’s air quality managers measure PM2.5, and use these values to determine current air quality.
The Air Quality Index is the standard tool to communicate air quality conditions with the public. The simple, color-coded tiers indicate the quality of the air, individuals or groups who may experience health effects, and provide guidance on appropriate health actions. Visit AirNow to explore the current and forecast AQI for Yosemite National Park.
Yosemite Observer Dashboard: Air Quality