During a period of intense drought and widespread heatwaves, over 80 wildfires were triggered across 13 states in the western and northern United States as well as numerous regions in western Canada.

These record-breaking wildfires initiallyresulted in dangerously unhealthy air quality over thousands of square miles in the U.S. states of California, Oregon, Washington, and Montana as well as the Canadian provinces of British Columbia and Alberta – regions typically known for their natural beauty and relatively clean air during most of the year.

As pictured below, fires in western and northern Canada worsened air quality across the eastern continent continually through much of July.

Pictured: Poor air quality across Canada as well as the northern, Upper Midwest, and East Coast of the U.S. on the morning of 21 July 2021. Though air quality on the East Coast had become a little less dangerous by July 27, poor air quality conditions had shifted deeper to the south into Florida. Source: IQAir.

Pictured: Cities affected by wildfires burning throughout the western and northern U.S. dominated the top 10 most polluted cities in the U.S. on 5 August 2021, with AQI often reported as “Hazardous” – indicating emergency-level air pollution. Source: IQAir

Wildfire smoke spreading across North America

As wildfires grew in North America’s northern and western forests, smoke drifted thousands of miles east, bringing unhealthy air quality to the East Coast and Upper Midwest.

Cities such as Cleveland, Pittsburgh, Toronto, Boston, Philadelphia, and Washington D.C. all reported air quality in the “Unhealthy for Sensitive Groups” range (101-150) and “Unhealthy” range (151 to 200).

In the following week, smoke continued to drift south and affect Southern states like Georgia.¹

The images below illustrate how air quality across the Upper Midwest and East Coast changed in a week from Tuesday, July 20 to Tuesday, July 27.

Pictured: Wildfire smoke spread south and east across the Midwest and Eastern Seaboard on Tuesday, 20 July (above) through Tuesday, 27 July (below), severely impacting air quality across the region. Source: IQAir

New York City frequently measured among the most polluted cities in the world on July 20 and 21. The city frequently shifted among the top five spots during those two days.

On the East Coast, air quality alerts were issued for counties in New Jersey, Maine, and Massachusetts for July 21.^2,3,4

Bootleg Fire

Among the largest of these summer conflagrations is the Bootleg Fire near Klamath Falls in Oregon. First ignited on July 6, 2021, the Bootleg fire merged with a smaller fire and grew to over 410,000 acres by July 27 – an area bigger thanNew York City or Los Angelesand more than half the size of Rhode Island.^5,6

Pictured: Particle pollution levels near Klamath Falls, OR on the morning of 19 July 2021. The Bootleg Fire area is represented by fire icons (top right). Source: IQAir

The Bootleg Fire has been fueled by months of drought in Oregon and the Pacific Northwest, which had dried out hundreds of thousands of acres of forests and grasslands and created a tinder box that allowed the fire to explode in size. The blaze was at 53 percent containment by Tuesday, July 27.⁷

By July 19, 2021, air quality in Klamath Falls and areas nearest to the wildfires had somewhat improved due to wind direction. Air Quality Index (AQI) measurements were mostly recorded as “Moderate” (51-100) to “Unhealthy for Sensitive Groups” (101-150).

But due to northeastward winds, huge plumes of smoke from the Bootleg Fire had allowed extreme levels of PM2.5 – one of the most common and dangerous pollutants in wildfire smoke – to build in nearby cities like Boise, Idahofor a week. The city experienced air quality index (AQI) typically measuring in the “Unhealthy for Sensitive Groups” and “Unhealthy” ranges across thousands of square miles.

Pictured: Widespread poor air quality in Boise and surrounding areas for hundreds of square miles on 27 July 2021. Source: IQAir

Trail Creek Fire

Located around 20 miles outside of Wisdom near the border with Idaho, the Trail Creek fire in Southwestern Montana had only grown to about 23,000 acres by July 19, 2021 – not even a tenth of the size of the Bootleg Fire.⁸ The fire had grown to nearly 33,000 acres by July 27.

However, the Trail Creek fire has produced plumes of smoke that, along with smoke traveling northward from the Bootleg Fire, is resulting in emergency-level air quality conditions across much of Montana. Cities affected include populated areas like Missoula (pop: ~73,000) and Butte (~33,000) as well as Kalispell – known for its proximity to Glacier National Park.

Pictured: Poor air quality in western Montana due to wildfire smoke from the Trail Creek fire (27 July 2021). Air quality is widely reported in the “Unhealthy” range. Source: IQAir

Cub Creek and Cedar Creek wildfires

The Cub Creek fire first ignited north of Winthrop in northeastern Washington state on the afternoon of Friday, July 16, 2021. The fire grew to over 51,000 acres, with only 11 percent containment by July 27.⁹

To the northwest of Winthrop, the smaller Cedar Creek fire was about 33,500 acres and only 13 percent contained on July 27.

By July 20, evacuations were ordered for roads near the fires. The wildfires also created extremely dangerous air quality conditions in neighboring towns through July 27 – with AQI measuring well into the 300-400 range considered “Hazardous” and some stations reporting AQI as high as the 600 range.¹⁰

Pictured: Hazardous-level air quality conditions in Winthrop, WA and the surrounding regions due to the Cub Creek and Cedar Creek Fires. Source: IQAir

Tamarack Fire

A smaller but potentially dangerous fire, the Tamarack Fire in northern California and Nevada began weeks ago during the Fourth of July holiday weekend because of a lightning strike.

However, the fire recently grew substantially from July 16-20 to over 40,000 acres due to continued drought conditions in California. The fire expanded into the popular lakeside resort town of South Lake Tahoe, CA, prompting evacuations throughout the area as the fire remained at zero percent containment into Wednesday, July 21.^11,12

The fire expanded further to 68,000 acres by July 27, but was also 54 percent contained.¹³

Toxic wildfire smoke has since blown eastward into the highly populatedCarson City, Nevadaarea and also caused “Hazardous” levels of air pollution in the nearby suburbs ofMinden and Gardnerville, with some areas reporting AQI measurements as high as 320.

Pictured: Smoke from the Tamarack Fire has blown into South Lake Tahoe and the surrounding cities of Carson City, Minden, and Gardnerville. Source: IQAir

Smoke from the fire also affected the nearby Reno-Sparks metropolitan area in western Nevada. Air quality of “Unhealthy for sensitive groups” conditions were recorded across the entire city by July 27.

Pictured: Air quality across Reno-Sparks, NV – AQI measurements of “Moderate” transitioned to “Unhealthy for sensitive groups across the city Source: IQAir

Dixie Fire

The largest fire in California, the Dixie Fire, burned 208,000 acres of Plumas and Buttes Counties by July 27.^14,15 Ignited on July 13, the blaze quickly grew over the prior weekend when it merged with the Fly Fire. It then became the 14^th largest fire in California history – and at only 23 percent contained, the blaze has the potential to rank as one of the state’s top ten.

Smoke from the Dixie Fire also fed into poor air quality experienced in Reno, Sparks, and the Lake Tahoe areas. Residing just to the northeast of the Dixie Fire, residents living along the shores of Lake Almanor found their air was in the “Unhealthy” to “Very unhealthy” AQI range on July 27.

Pictured: The Dixie Fire created “Unhealthy” and “Very unhealthy” conditions for communities along Lake Almanor, California on July 27. Source: IQAir.

Canadian wildfires

Although numerous active wildfires in Canada aren’t individually as large as the Bootleg Fire in Oregon, they have created a formidable air quality hazard in much of Canada.

With thousands of reported fires in every province and territory west of Quebec, air quality has steeply declined in the prairie provinces’ major cities.

Pictured: Poor air quality was recorded across southern British Columbia, northern Alberta and Saskatchewan, and portions of southern Manitoba and Ontario. (19 July 2021). Source: IQAir

Numerous uncontrolled fires have been concentrated along southern British Columbia, northern Saskatchewan, west-central Manitoba, and far-western Ontario.

Fires in British Columbia, primarily along the Washington and Montana borders, resulted in a provincial state of emergency declaration on Tuesday, July 20.¹⁶

A combined 667,184 acres of British Columbia has been scorched by wildfires, where there have been 300 active wildfires and 90 evacuation alerts.¹⁷ Smoke from the fires has swept south and east to impact major population centers downwind.

Major cities with “unhealthy” air quality as of Monday morning, July 19, 2021 included:

• Edmonton, Alberta
• Calgary, Alberta
• Winnipeg, Manitoba
• Toronto, Ontario

Air quality in Regina, Saskatchewan and Ottawa, Ontario registered as “unhealthy for sensitive groups.”The smaller British Columbia cities of Vernon and Kamloops recorded “very unhealthy” air quality as well.

Pictured: Wildfire smoke drifting across province borders in neighboring Saskatchewan and British Columbia created unhealthy air quality conditions across most of Edmonton, Alberta on Monday morning. (19 July 2021). Source: IQAir

Pictured: Unhealthy air quality conditions were recorded by air quality monitoring sensors in Calgary, Alberta on Monday morning. (19 July 2021). Source: IQAir

The takeaway

Due to months of drought and heat, wildfires have blanketed enormous areas of the western and northern U.S. as well as parts of Canada in extremely poor air quality from toxic smoke.

Here’s what you can do to help protect yourself from wildfire smoke if you’re affected by these fires:

• Follow local evacuation orders promptly.
• Monitor your air quality to know how wildfire smoke is affecting the air in your neighborhood.
• Close windows and doors to keep outdoor wildfire smoke from seeping indoors.
• Run an air purifier for wildfire smoke to help filter smoke particles that may enter your home from outdoors.
• Wear an air pollution mask outdoors if you are directly exposed to wildfire smoke. Even short periods of smoke inhalation can cause heart or lung damage.