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      • Current Air Quality and Smoke Monitoring

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:

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 Webcams

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 in the Yosemite Valley, looking east toward Half Dome

High Sierra webcam at Sentinel Dome near Glacier Point, looking east out over the High Sierra

El Capitan webcam at Turtleback Dome, looking east toward El Capitan and Half Dome

Crane Flat Helibase webcam, is pointed SSE toward the South Fork Merced River. (Available seasonally.)

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 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.

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:	...as 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.

 

Campfires

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 AIRNow.gov.

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):

 

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

NASA

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.