CLICK HERE if you are having a problem viewing the photos on a mobile device

A major wildfire burning on the western edge of Yosemite National Park has generated so much smoke that air pollution levels in Yosemite Valley are worse than in Beijing, one of the world’s most polluted cities.

At the height of summer tourist season, choking levels of soot have exceeded U.S. federal health standards in the valley — in some cases up to seven times higher than the recommended limit and well above what is classified by the U.S. Environmental Protection Agency as “hazardous” for all people, even healthy adults, to breathe.

Conditions are so bad that health officials are discouraging people from coming to the park until the fire is under control.

“I’ve never seen numbers this high, and I’ve been doing this for 30 years,” said Dave Conway, deputy officer for the Mariposa County Air Pollution Control District, on Monday.

The Ferguson fire began July 13. It has burned an area larger than the city of San Francisco. And as flames ravage through brush and dead trees from California’s recent drought, the fire is generating an enormous amount of soot.

Air quality monitoring equipment at the Yosemite Visitor Center has registered particulate pollution in the valley every day since July 15 at levels at least twice the concentration measured by the air monitor on top of the U.S. embassy in Beijing over the same time period. Last Wednesday, the peak particulate levels in Yosemite Valley were nearly five times as high as in China’s capital city — 518 vs. 106 micrograms per cubic meter of particulates in the air. The EPA classifies anything over 35 averaged over 24 hours to be unsafe.

What should visitors do?

“Go home,” said Conway. “I hate to be that blunt about it, but it is not going to be the experience they want and the air is going to be hazardous at times. If people have any known heart concerns, breathing concerns or if they have kids, people should avoid the park.”

Exposure to particle pollution can cause serious health problems, including asthma attacks, acute bronchitis and heart attacks. It also can increase the risk of respiratory infections.

In addition to an advisory from Mariposa County’s Health Department, the San Joaquin Valley air pollution control district issued an air quality alert last Tuesday for the foothills and mountain areas of Stanislaus, Merced, Madera, Fresno and Tulare counties due to the Ferguson fire.

On Monday Yosemite National Park remained open. But that could change.

One of the main roads into the park, Highway 140, is closed, as is Glacier Point Road. Views of the Yosemite Falls, Half Dome and other landmarks are all but gone, and tourists in the valley increasingly are wearing bandannas and medical masks. Bike rentals and open tram tours have been limited, and restaurant hours are being cut back, said Scott Gediman, a Yosemite park spokesman.

“It’s summer in Yosemite,” Gediman said. “We have lots of international visitors. People have been planning their trips for months and years. But if people can make alternate plans, they should consider that at this point.”

The fire jumped Highway 140 near El Portal on Friday afternoon and is burning north toward Highway 120. If it keeps advancing and closes Highway 120 or Highway 41 in the south, Gediman said, that would leave only one road in and out of Yosemite Valley, a dangerous situation that he said could prompt officials to temporarily close the park for a few days, as they did in March for two days during flooding in Yosemite Valley.

On Monday afternoon, the fire was burning four miles from Yosemite’s Arch Rock entrance on Highway 140. It blackened steep terrain in the Stanislaus and Sierra national forests as temperatures neared 100 degrees. More than 3,000 firefighters battled the blaze, which was at 33,743 acres and only 13 percent contained.

Fire crews positioned engines around Yosemite View Lodge, Cedar Lodge — both of which were under mandatory evacuation — and other businesses near El Portal along Highway 140.

“I wish I could say it will be completely contained tomorrow, but I think we’ll be here for at least another week, maybe longer,” said Alex Olow, a spokesman for the Sierra National Forest.

Related Articles Opinion: Why Newsom should sign bill protecting Coyote Valley

Bobcat fire containment more than doubles; federal investigators look at utility equipment as cause

Santa Cruz CZU fire fully contained, work remains

100 firefighters from Mexico arrive to help battle Castle fire in Tulare County

Yosemite National Park to reopen Friday, with more campsites available In addition to 3,066 firefighters, there are 199 engines, 46 water tenders, 16 helicopters, 66 crews, and 43 bulldozers battling the blaze, which is the biggest fire around Yosemite since the massive Rim Fire burned 257,000 acres in 2013. Because of the remote terrain, with steep canyons and ridges in national forest land, no homes have burned, although some communities, including Yosemite West, are at risk.

Start your day with the news you need from the Bay Area and beyond.

Sign up for our Morning Report weekday newsletter.

One firefighter has died. Braden Varney, 36, a bulldozer operator for CalFire, died July 14 when his bulldozer rolled down a hill while he was cutting fire lines. Varney, a Mariposa resident who leaves behind a wife and two small children, was honored Monday at a ceremony in Modesto attended by firefighters from across California.