Tioga & Glacier Point Roads Closed for the Winter
The Tioga Road (Highway 120 through the park) and Glacier Point Road are closed due to snow; they usually reopen late May or June. You can check on current road conditions by calling 209/372-0200 (press 1 then 1). More »
Current Air Quality and Smoke Monitoring
The winter wet season is almost here and fire season is nearly over (10/22/2013). During the 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 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:
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:
Yosemite Air Quality Monitoring: 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.
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.
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 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 front-country 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 at Yosemite Valley Schoolyard 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 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.
Ozone at Turtleback Dome west of the Yosemite Valley, overlooking the Merced River Canyon at 5,266 feet (1605 m):
Ozone at Yosemite Valley Schoolyard, near Yosemite Falls, at 3977 ft (1212 m) is no longer available in real time, but archived data can be found at: http://www.nature.nps.gov/air/monitoring/network.cfm
Online Tools to Locate a Fire Nearby
Did You Know?
The Merced River above Nevada Fall and South Fork Merced River above Wawona, numerous small meadows and adjacent riparian habitats occur. Owing their existence to the river and its annual flooding, these habitats help support eight special status animal species: harlequin ducks, black swifts, bald eagles, osprey, willow flycatchers, yellow warbler, western red bat, and Sierra Nevada mountain beaver.