Denver experienced the worst air quality of any major city in the world due to smoke from western wildfires

Denver experienced the worst air quality of any city in the world for several hours Saturday as heavy smoke from raging western wildfires polluted the city.

IQAir, a Swiss air quality technology company, determined that Denver’s air was the most polluted early Saturday at an Air Quality Index of 167. The measurement is by US standards, where a higher number indicates poorer air quality.

The company tracks the AQI for 94 major world cities. Later on Saturday, the city of Johannesburg, South Africa, moved to the top spot with a US AQI of 178.

The polluted air is a symptom of the 107 wildfires that are currently burning in the US and which have scorched 2.1 million acres as of Saturday, according to the National Interagency Fire Center.

Smoke from western wildfires obscures the skyline of Denver on August 7, 2021.

And it’s likely that the drought conditions fueling the fires will get worse before they get better.

“The fire outlook continues to reflect warmer and drier conditions leading to the high potential for severe wildfire activity throughout the western United States through the rest of summer and into the fall. Widespread high temperatures observed across areas in the West and with periods of lightning activity continue to exacerbate the wildfire situation,” the NIFC said on its website.

The wildfire season has been devastating for California, where the Dixie Fire – the nation’s largest active fire – continues to grow and destroy anything in its path.

The fire, which is burning in four California counties, swelled to 447,723 acres Saturday and remains 21% contained, according to Cal Fire.

TOPSHOT - Firefighters work the scene as a home is engulfed in flames during the Dixie fire in Greenville, California on August 4, 2021. - The Dixie fire burned through dozens of homes and businesses in downtown Greenville and continues to forge towards other residential communities. Officials in northern California on August 4, 2021 warned residents of two communities in the path of the raging Dixie fire to evacuate immediately as high winds whipped the flames onwards. (Photo by JOSH EDELSON / AFP) (Photo by JOSH EDELSON/AFP via Getty Images)

'We lost Greenville': Dixie Fire wipes out much of Northern California community

Five people who were missing after the fire tore through the historic town of Greenville, California, have been found safe, the Plumas County Sheriff’s Office announced Saturday. A total of 21 unaccounted-for people are now confirmed safe, while authorities are still searching for five others, the office said.

Greenville was nearly leveled when the fire swept through it. In the community’s commercial center at Main Street and State Route 89, nearly every business appeared to have collapsed or been gutted, with flames still flickering in the debris up and down the sides of both streets, video recorded Wednesday by storm chaser Brandon Clement showed.

How to support western wildfire victims

Fires across the region prompted California’s Placer County Public Health and the Placer County Air Pollution Control District to issue an air quality advisory Thursday, forecasting hazardous smoke impacts and warning residents to stay indoors.

“Sad to say, the prediction is correct,” Ann Hobbs, associate planner at the Placer County Air Pollution Control District, told CNN. Hobbs said officials had anticipated a change in the wind would bring poor air quality and smoke to residents living in the area.

“Avoid all unnecessary outdoor activity,” said Hobbs, adding that the air quality is the worst the area has seen all year.

The Alisal Fire burns near Goleta, California, on Tuesday, October 12.

A firefighter puts out a roadside fire in Goleta, California, on Wednesday, October 13.

An air tanker drops retardant on a wildfire in Goleta.

James Grooms looks through the remains of his home at the Rancho Marina Mobile Home & RV Park following the Brannan Fire in Sacramento County, California, on Tuesday, October 12.

Firefighter Tyler McManigal battles the Alisal Fire in Gaviota, California, on October 12.

A forest of ashen trees stands in the wake of the Windy Fire, south of California Hot Springs, on September 27.

A volunteer attempts to evacuate horses to safety as the Windy Fire expands in California's Sequoia National Forest on September 25.

Operations Section Chief Jon Wallace looks at the General Sherman giant sequoia tree at Sequoia National Park on September 22. The base of the tree, the world's largest by volume, was wrapped in an aluminum-based burn-resistant material to protect it from wildfires.

Firefighters spray water as flames from the Windy Fire push toward a road in California's Sequoia National Forest on September 22.

Firefighters battling the Windy Fire extinguish a spot fire in the Sequoia National Forest on September 19.

The Windy Fire burns in the Trail of 100 Giants grove in the Sequoia National Forest on September 19.

A helicopter drops water on the KNP Complex Fire burning in Sequoia National Park on September 15.

Flames from the KNP Complex Fire burn along a hillside in the Sequoia National Park on September 14.

This aerial photo, taken on September 4, shows the Dixie Fire on Horton Ridge in Plumas County, California.

Riley Cantrell cries while she and boyfriend, Bradley Fairbanks, view what's left of her mother's home in Greenville, California, on September 4. It was destroyed by the Dixie Fire.

A firefighter is seen as the Caldor Fire rages near California's Silver Lake on September 2.

A helicopter flies over Wrights Lake while battling the Caldor Fire in California's Eldorado National Forest.

Embers fly from a tree as the Caldor Fire burns along Highway 50 in California's Eldorado National Forest.

Veronica Foster, an evacuee from South Lake Tahoe, California, hugs her dog, Gracie, as she and her co-workers gather outside an evacuation center in Gardnerville, Nevada, on August 31. The governors of California and Nevada declared states of emergency as the fast-moving Caldor Fire prompted officials to tell everyone to get out of South Lake Tahoe.

Jason Marone of the Roseville Fire Department hoses down a hot spot in Meyers, California, on August 31.

A tree burns in a blackened forest at dawn on August 30 after the Caldor Fire tore through Twin Bridges, California.

A firefighter winds up hose at a spot fire near Meyers, California, on August 30.

The Caldor Fire burns homes along a ridge near South Lake Tahoe on August 30.

South Lake Tahoe residents are stuck in gridlock while attempting to evacuate the city on August 30.

A tanker makes a fire-retardant drop near Lytle Creek, California, on August 26 as efforts continued to stop the South Fire.

A firefighter tries to extinguish flames at a burning house as the South Fire burned in Lytle Creek, California, on August 25.

From left, Astrid Covarrubias, Jose Lamas and Maria Covarrubias walk through smoke after visiting their burned-out home in Lytle Creek on August 25.

The French Fire continues to spread near Wofford Heights, California, on August 25.

Firefighters are seen behind the flames of a backfire they were setting to battle the French Fire near Wofford Heights.

Crews battle California's Caldor Fire as it moved east toward Lake Tahoe on August 23.

This aerial photo, taken on August 19, shows burned homes at the Creekside Mobile Home Park a day after they were destroyed by the Cache Fire in Clearlake, California.

Firefighters dig a containment line on the Caldor Fire near Pollock Pines, California, on August 18.

Smoke and haze from wildfires obscure the Golden Gate Bridge and the San Francisco skyline on August 18.

In this long-exposure photo, embers light up hillsides as the Dixie Fire burns near Milford, California, on August 17.

Destiney Barnard holds Raymond William Goetchius while stranded at a gas station in Doyle, California, on August 17. Barnard's car broke down as she was helping Raymond and his family flee the Dixie Fire.

Destroyed property is seen August 17 after the Caldor Fire passed through Grizzly Flats, California.

Firefighters spray water on trees being burned by the Dixie Fire near Janesville, California, on August 17.

As the KNP Complex Fire approaches, Forest Service firefighters Armando Flores, right, and Heron Hilbach-Barger clear vegetation around structures at the Ash Mountain headquarters in Sequoia National Park, Calif., on Sept. 15, 2021. The blaze is burning near the Giant Forest, home to more than 2,000 giant sequoias.

A firefighting helicopter flies in front of the sun, which was shrouded in thick wildfire smoke near Lakeview, Oregon, on August 15.

Wind blows smoke away for a moment, revealing damage from the Parleys Canyon Fire in Utah on August 14.

Crews battle a fire in Newhall, California, on August 12.

A table and chairs sit in front of a destroyed home in Greenville, California, on August 12.

A firefighter battles the Dixie Fire near Taylorsville, California, on August 10.

Smoke plumes rise from the Kwis Fire near Eugene, Oregon, on August 10.

A firefighter works to extinguish a controlled burn, a preventative measure, to protect a home in Greenville, California, on August 9.

Firefighters battling the Dixie Fire clear a fallen tree from a roadway in Plumas County, California, on August 6.

Flames from the Dixie Fire consume a pickup truck on Highway 89, south of Greenville, California, on August 5.

Operations Chief Jay Walter passes the historic Sierra Lodge as the Dixie Fire burns through Greenville, California, on August 4. The fire leveled multiple historic buildings and dozens of homes in central Greenville.

Firefighters work at a Greenville home that was engulfed by the Dixie Fire on August 4.

The Dixie Fire burns near Taylorsville, California, on July 29.

California Gov. Gavin Newsom, left, and Nevada Gov. Steve Sisolak tour an area destroyed by the Tamarack Fire in Gardnerville, Nevada, on July 28.

Firefighter Brentt Call walks through a burned-over area of the Bootleg Fire near Klamath Falls, Oregon, on July 27.

Cal Fire Capts. Tristan Gale, left, and Derek Leong monitor a firing operation in California's Lassen National Forest on July 26. Crews had set a ground fire to stop the Dixie Fire from spreading.

Firefighters try to reach a fire site in Quincy, California, on July 25.

Volunteers sort clothing at a donation shelter for those affected by the Bootleg Fire in Bly, Oregon.

Scott Griffin surveys his property, which was destroyed by the Bootleg Fire in Sycan Estates, Oregon.

Flames consume a home as the Dixie Fire tears through the Indian Falls community of Plumas County, California, on July 24.

People stand behind the fire line as flames from the Steptoe Canyon Fire spread through dry grass in Colton, Washington, on July 22.

Plumes of smoke from the Dixie Fire rise above California's Plumas National Forest, near the Pacific Gas and Electric Rock Creek Power House, on July 21.

Firefighters walk near a wildfire in Topanga, California, on July 19.

A firefighter does mop-up work in the Fremont-Winema National Forest, which has been struggling with the Bootleg Fire in Oregon.

A car is charred by the Bootleg Fire along a mountain road near Bly, Oregon.

Nicolas Bey, 11, hugs his father, Sayyid, near a donated trailer they are using after their home was burned in the Bootleg Fire near Beatty, Oregon.

Firefighters extinguish hot spots in an area affected by the Bootleg Fire near Bly, Oregon.

A bear cub clings to a tree after being spotted by a safety officer at the Bootleg Fire in Oregon.

Firefighters work to protect Markleeville, California, from the Tamarack Fire on July 17. The Tamarack Fire was started by a lightning strike.

The Tamarack Fire burns in Markleeville, near the California-Nevada border, on July 17.

A member of the Northwest Incident Management Team 12 holds a map of the Chuweah Creek Fire as wildfires devastated Nespelem, Washington, on July 16.

A cloud from the Bootleg Fire drifts into the air near Bly, Oregon, on July 16.

Firefighters spray water from the Union Pacific Railroad's fire train while battling the Dixie Fire in California's Plumas National Forest on July 16.

Horses climb a hillside that was burned by the Chuweah Creek Fire in eastern Washington.

Fire from the Bootleg Fire illuminates smoke near Bly, Oregon, on the night of July 16.

A firefighter battles the Bootleg Fire in the Fremont-Winema National Forest, along the Oregon and California border, on July 15.

A firefighting aircraft drops flame retardant on the Bootleg Fire in Bly, Oregon, on July 15.

Firefighters dig away at hot spots underneath stumps and brush after flames from the Snake River Complex Fire swept through the area south of Lewiston, Idaho, on July 15.

Burned cars sit outside a home that was destroyed by the Chuweah Creek Fire in Nespelem, Washington.

Evacuee Dee McCarley hugs her cat Bunny at a Red Cross center in Klamath Falls, Oregon, on July 14.

An airplane drops fire retardant on the Chuweah Creek Fire in Washington on July 14.

Operations Section Chief Bert Thayer examines a map of the Bootleg Fire in Chiloquin, Oregon, on July 13.

Fire consumes a home as the Sugar Fire, part of the Beckwourth Complex Fire, tears through Doyle, California, on July 10. It's the second time in less than a year that the small town has been ravaged by a wildfire.

Men hug a member of the Red Cross at a Bootleg Fire evacuation center in Klamath Falls, Oregon.

Embers blow across a field as the Sugar Fire burns in Doyle, California, on July 9.

Firefighters monitor the Sugar Fire in Doyle, California, on July 9.

In this long-exposure photograph, taken early on July 2, flames surround a drought-stricken Shasta Lake during the Salt Fire in Lakehead, California.

In pictures: Wildfires raging in the West

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Meanwhile, some areas within British Columbia are under evacuation orders or alerts as the White Rock Lake wildfire continues to spread, according to the British Columbia Wildfire Service.

The fire, burning near Vernon, has scorched about 135,900 acres. The city expanded its evacuation alert Friday night to include most of the city, according to a news release.

The expanded evacuation alert was made “out of an abundance of caution based on the advice of BC Wildfire due to increased fire activity and increased ember debris,” the City of Vernon tweeted.

Brisa Colon, Andy Rose and Camille Furst contributed to this report.