Dangerous air quality forces closure of section of national park, which gets more than half a million visitors in July alone

Yosemite national park has been partially closed and officials have ordered more mandatory evacuations as wildfires continue to sweep across California this week. Fueled by dry conditions and high temperatures, smoke has settled over the popular tourist destination, causing unsafe conditions for visitors and workers, prompting officials to issue a temporary closure and evacuate the remaining tourists beginning on Wednesday at noon.

The California department of forestry and fire protection said on Wednesday that the blaze has burned 60 square miles (155 sq km). It is 25% contained.

National Park Service representatives announced at a public meeting on Tuesday that the Yosemite valley, as well as the Wawona area, would be closed temporarily until air quality conditions improve. Now new evacuations cover communities outside the park’s north side.

Working against steep, difficult terrain and unrelenting heat that reaches into triple digits during the day, fire crews have been battling the Ferguson fire – one of 50 currently burning in the US – for the past 12 days.

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The park has remained mostly open throughout the past week, despite warnings from local public health officials, but campsites and lodges emptied out after disappointed tourists were ordered to leave by the midday deadline. Complicated by high temperatures, air quality measurements have been in “unhealthy” to “very unhealthy” ranges through the past several days.

“We see these inversion layers that are created because of the weather, that just keep the smoke trapped down toward the ground,” Ginnie Day, a representative from the Mariposa county public health department, told the Guardian. “Our air pollution control deputy is pretty busy right now, but he’s said he’s never seen numbers this high – and he’s been doing this for 30 years.

“It’s unfortunate,” Day added, “because this is summer and for our town it does impact the businesses that depend on the tourism that is created by the beautiful Yosemite national park nearby us.”

This is partially why, according to park representatives, the decision to close popular areas of the park was not made sooner.

“We’ve got literally thousands of visitors here every day and people coming from all over the world.”

Late summer is peak tourist season in the park, and it is typically swarmed by tourists. In previous years, July has averaged close to 600,000 visitors. At least a thousand campground and hotel bookings will be canceled to say nothing of the impact on day visitors, park workers and small businesses along the highway, a park spokesman, Scott Gediman, said. Rangers went to campsites one at a time to inform visitors of the closures. Hotel guests got phone calls and notes on their doors.

Facebook Twitter Pinterest Smoke from the Ferguson fire. A section of the park will be closed until air quality improves. Photograph: Reuters

Although the fire has not reached the park yet, officials wanted to ensure firefighters had access to the area for defensive operations as they battle the flames. For those still in the area, Gediman said, cooling centers are being set up where people can breathe clean air and public health officials were available to aid workers.

Officials are expecting the closures to remain in effect until at least Sunday evening. “Conditions are changing and we felt that based upon the predictions for air quality and the weather in the next few days, we felt safe in saying these closures will be in effect until Sunday,” Gediman said. “But we want people to know these are temporary … people come from all over the world to visit Yosemite and so we certainly want to accommodate visitors the best we can, but the health and safety of park visitors, park employees and firefighters is our main concern.”

The last time the 7.5-mile-long (12km-long) valley was closed because of fire was 1990, Gediman said.