Smoke Overview

Smoke drifting away from smoke plume in Yosemite high country


Fire and smoke are as much a part of the Yosemite ecosystem as water and ice. Every year, thousands of lightning strikes occur within park boundaries, igniting vegetation made tinder-dry by Yosemite’s long, hot summers. Inevitably, some of these strikes cause fires, which in turn emit smoke.


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


Visual, interactive information about current weather, stream flow, fires, and air quality conditions; all on one site! 


Smoke and Your Health

Healthy people are not generally at risk to short-term exposure to smoke. People with asthma or other respiratory conditions should consult the local air quality report and speak with their doctor. Exposure to smoke may cause burning eyes, runny nose, bronchitis, or inflame preexisting heart and lung diseases. Strenuous exercise aggravates smoke’s impacts, as quick and deeper breathing increases the amount of particulate matter inhaled.
Tips for minimizing smoke exposure:

  1. Stay indoors.
  2. Wear a well-fitting N95 respirator. When used correctly, N95s filter particulate matter. Cloth and surgical masks do not protect against smoke’s health effects.
  3. During the day: If you must exercise strenuously on smoky days, try to exercise when it's less smoky. Depending on fire and weather conditions, a pattern may develop for when it's less smoky each day (often, but not always, in the afternoons).
  4. During the night: Avoid extended exposure to outdoor air in canyon bottoms like Yosemite Valley and other low-lying areas near rivers and lake basins—these areas commonly experience the highest fine-particle levels during calm, smoky periods.

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Last updated: August 21, 2023

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