Air quality alerts and advisories: No fires at this time. Come back next fire season (2012)!

Ozone and fire season in Yosemite are now over. During late spring, summer, and fall, local and regional-scale smoke plumes occasionally degrade air quality in Yosemite, sometimes to unhealthy levels. Ozone from sources to our west also occasionally degrade air quality, at least until the end of September. After that, days are usually too short and temperatures too low for ozone to reach unhealthy levels in Yosemite. Ozone and fire season usually begin again sometime in May.

Yosemite NP monitors smoke/fine particles and ozone as part of a nationwide effort to protect air quality and public health. Current nationwide conditions are mapped below:

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

 

Yosemite Air Quality Monitoring: Fine particles/smoke at the Yosemite Valley Visitor's Center

The chart below plots both the 1-hour and running 24-hour average PM_2.5 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.

 

Yosemite Webcams

View of the Merced River Canyon, looking west from Yosemite Turtleback Dome, at 5,266 feet in elevation, toward the Central Valley. Direct links to other Yosemite webcams are below: 

Ahwahnee Meadow webcam in the Yosemite Valley, looking east toward Halfdome

Sentinel Dome webcam near Glacier Point, looking east toward Halfdome

Turtleback Dome webcam above the west end of Yosemite Valley, looking east toward Halfdome

Crane Flat Helibase webcam, looking east into the park, toward latest wildland fires

Past images of these webcams are also archived on the SWFRS web site.

Yosemite Air Quality Monitoring: Ozone 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 75 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.

At Yosemite Valley Schoolyard, near Yosemite Falls (4000 ft):

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. More on ozone and its health effects at AIRNow.gov.

Where in Yosemite is ozone usually a concern? Historically, data shows that ozone is worst in the Yosemite front-country (i.e., Wawona, El Portal, Crane Flat, and Camp Mather). At sites like these, ozone is often found at 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 our 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, rarely unhealthy even on most polluted of days.

When is ozone usually a 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 front-country areas during late afternoon periods when high ozone might occur. 

Yosemite ozone forecasts: Check the California forecast map at airnow.gov for conditions likely affecting Yosemite front-country areas (see graphic to right for Yosemite's location).

Or, check the following shortcuts to the NOAA forecast website for current and projected conditions at the following pre-selected sites:

• Yosemite Valley
• Hetch Hetchy
• Tuolumne Meadows
• Wawona
• El Portal

Note that these products are experimental and may be unreliable.

A note on campfires and campgrounds: 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.

Online Tools to Locate a Fire Nearby

• MODIS satellite imagery often captures plumes from large fires via high-resolution (250m), color images of the Fresno/Yosemite area (2 images per day).
• Download fire maps and fire perimeters from GeoMAC's (Geospatial Multi-Agency Coordination Group) federal mapping tools.
• Get specific fire information on current Sierra Nevada fires from the Sierra Wildland Fire Reporting System (SWFRS).