Air Quality and Smoke Monitoring

During summer, ozone and fine particles from sources to our west occasionally degrade Yosemite air quality. Sometimes, smoke from local or regional fires also contribute. By the end of September though, ozone usually diminishes due to lower levels due to cooler fall temperatures, lower angle sunlight, and shorter days. Fires continue to occur in the fall before (or until) the rains come—as late as December in a dry year. Check back and scroll down to see the most current information on air quality and smoke impacts in Yosemite.

Yosemite National Park monitors smoke/fine particles and ozone as part of a nationwide effort to protect air quality and public health. Various agencies in California provide statewide smoke information. Current nationwide conditions are mapped below:

nationwide ozone from
Regional ozone, from
nationwide fine particles from
Regional fine particles, from
nationwide smoke plumes from NOAA Hazard Mapping System
Nationwide smoke plumes, from NOAA Hazard Mapping System
regional infrared satellite image from National Weather Service, Hanford
Regional infrared satellite image, from National Weather Service, Hanford


Yosemite Webcams

View west from Turtleback Dome

View of the Merced River Canyon, looking west from Yosemite Turtleback Dome, at 5,266 feet (1605 m) above sea level, toward the Central Valley. Direct links to other Yosemite webcams are below:
Ahwahnee Meadow webcam, courtesy Yosemite Conservancy
Ahwahnee Meadow webcam in the Yosemite Valley, looking east toward Half Dome
Sentinel Dome webcam, courtesy Yosemite Conservancy
High Sierra webcam at Sentinel Dome near Glacier Point, looking east out over the High Sierra
El Capitan (east) webcam, courtesy Yosemite Conservancy
El Capitan webcam at Turtleback Dome, looking east toward El Capitan and Half Dome
Crane Flat webcam, south over Merced River canyon from Crane Helibase
Wawona webcam, is looking south southwest over the Wawona area.
Yosemite Falls webcam, courtesy Yosemite Conservancy
Yosemite Falls Webcam looking north toward Yosemite Falls from the Yosemite Valley Lodge
Past images of these webcams are also archived on the SWFRS web site.

Yosemite Air Quality Monitoring

View current fine particles/smoke at the Yosemite Valley Visitor Center

The chart below plots both the 1-hour and running 24-hour average PM2.5 concentration, but only the 24-hour average should be used to compare with the standard. The standard is exceeded when the 24-hour concentrations go above 35 micrograms per cubic meter, as denoted by the line with the label NAT'L AMBIENT AIR QUALITY STANDARD. The background of the chart is color coded and relates to the EPA National Ambient Air Quality Standard for particulate matter, which is designed to protect human health.

10 day chart of fine particles at Yosemite Valley Visitor Center

View PM2.5 data from air monitors.

Air Quality Index
(AQI) Values
Levels of Health Concern Colors
When the AQI is in this range: ..air quality conditions are: symbolized by this color:
0 to 50 Good Green
51 to 100 Moderate Yellow
101 to 150 Unhealthy for Sensitive Groups Orange
151 to 200 Unhealthy Red
201 to 300 Very Unhealthy Purple
301 to 500 Hazardous Maroon

Note: Values above 500 are considered Beyond the AQI. Follow recommendations for the Hazardous category. Additional information on reducing exposure to extremely high levels of particle pollution is available here.



Some Yosemite campgrounds have many campsites and campfires. Emissions from many simultaneous campfires can degrade air quality on a local scale. This is especially true in the nighttime and early morning hours, when inversions trap and concentrate fine particles from those campfires near the ground, creating local conditions that are potentially unhealthy for sensitive individuals.


Ozone and Human Health in Yosemite

Because ozone pollution near the ground is usually only a concern on hot, sunny days, the ozone season runs May through September. Ozone is therefore rarely a human health concern in Yosemite during other times of the year. Learn more about ozone and its health effects at

Where in Yosemite is Ozone Usually a Concern?

Historically, data show that ozone is worst in the Yosemite frontcountry (e.g., Wawona, El Portal, Crane Flat). At sites like these, ozone is often reaches levels unhealthy for sensitive individuals (asthmatics or others with respiratory ailments). These unhealthy days often coincide with days that are unhealthy (Orange AQI) in the Central Valley, to the west, which is the primary source of this ozone.

In more sheltered areas like the Yosemite Valley and remote, high-elevations areas like Tuolumne Meadows, ozone is usually much lower, and is rarely unhealthy even on most polluted of days.

When is Ozone Usually a Human Health Concern in Yosemite?

Highest levels of ozone on a given day usually occur in late afternoon and evening. If you have a respiratory condition, such as asthma, consult a doctor before exercising strenuously in frontcountry areas during late afternoon periods when high ozone might occur. Between the end of September/early October and May, ozone is usually not a human health concern in Yosemite.


Yosemite Ozone Monitoring

Yosemite has been monitoring ozone at three sites for several years now: seasonally in Yosemite Village and Glacier Point, and year-round at Turtleback Dome.

The charts below plots both the 1-hour and running 8-hour average ozone concentration, but only the 8-hour average should be used to compare with the standard. The standard is exceeded when the 8-hour concentrations reach or go above 70 parts per billion, as denoted by the line with the label NAT'L AMBIENT AIR QUALITY STANDARD. The background of the chart is color coded and relates to the EPA National Ambient Air Quality Standard for ozone, which is designed to protect human health. The National Park Service tracks the days when the ozone standard is exceeded in the parks.

Ozone at Turtleback Dome west of the Yosemite Valley, overlooking the Merced River Canyon at 5,266 feet (1605 m):

10 day chart of ozone at Turtleback Dome

Satellite image of smoke
Click to see today's NASA satellite imagery of the Yosemite area.


Online Tools to Locate a Fire Nearby

Last updated: March 8, 2018

Contact the Park

Mailing Address:

PO Box 577
Yosemite National Park, CA 95389


(209) 372-0200

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