Much of Colorado experienced unhealthy air quality conditions in late 2020, as four major wildfires grew in size and burned throughout the state. Plumes of smoke from the cumulative 395,600 scorched acres could be seen from space, while the health implications, including elevated levels of particulate matter pollutants such as PM2.5 (particulate matter with a diameter size of 2.5 microns or smaller) and PM10 (particulate matter with a diameter size of 10 microns or smaller) in Colorado and surrounding areas were tracked on IQAir’sair quality heat map.¹

Wildfire smoke from all four Colorado fires, spreading across the state.²

Despite diligent efforts of thousands of firefighters across Colorado working to contain the fires, hot and dry conditions paired with little precipitation and gusty winds contributed to their explosive growth.³ Two of the four fires would surpass previous records to become the two largest fires in Colorado history.

In response to overspread firefighting resources and volatile conditions, Colorado Gov. Jared Polis announced a 30-day fire ban, starting on Thursday, August 20. Campfires, fireworks and other open sources of combustion across the entire state were prohibited until September 20. The fire-ban sought to greatly reduce the chance of human-caused fires, which are responsible for a vast majority of US wildfires.⁴

For the first time in years, the entire state of Colorado experienced a drought, with nearly 25 percent of the state in “extreme drought” conditions at the time of the fires.⁵ This was a sharp contrast from the year before, 2019, which was nearly drought-free due to El Niño.

Wildfires have been increasingly prevalent in the Western US. Their increased size and frequency over the last two decades has coincided with rising temperatures and changing weather patterns, as a result of anthropogenic climate change. Efforts to slow and reverse this trend will be important to combat the pervasiveness and environmental destruction posed by wildfires in the future.

Pine Gulch: 139,007 Acres⁶

The Pine Gulch fire burning 18 miles north of Grand Junction, contributing to “orange” pollution levels in the area.

The Pine Gulch fire on the Western Slope, just miles north of Grand Junction, grew to be the second largest in state history on Wednesday morning, August 19, after explosive expansion the night before.⁷ During the night of August 18, the fire grew over 30,000 acres due to 40 mph thunderstorm winds.

Colorado’s previously largest recorded fire was the 2002 Hayman fire, which burned 137,760 acres. The Pine Gulch Fire surpassed the Hayman Fire by reaching 139,007 acres before containment on September 23, 2020.⁸ The Pine Gulch Fire would, in turn, be overtaken by the Cameron Peak Fire later in 2020.

What is believed to have started by lightning strike on July 31 grew uncontrollably due to a dangerous combination of the area’s steep and remote terrain, arid conditions, volatile underbrush, and extraordinarily high temperatures during the summer of 2020. Such conditions made it difficult to predict the fire’s behavior and thwart its growth.

Clifton, six miles east of Grand Junction, registered as the most polluted city in Colorado on Wednesday, August 19, with air quality levels in the “unhealthy” AQI category. Grand Junction’s air quality fared only slightly better.

Smoke from wildfires can travel thousands of miles from the source, impacting air quality in cities that are distant from the flames.

Clifton, six miles east of Grand Junction, registered as the most polluted city in Colorado, on Wednesday, August 19, with air quality levels in the “unhealthy” AQI category.

Clifton, six miles east of Grand Junction, registered as the most polluted city in Colorado, on Wednesday, August 19, with air quality levels in the “unhealthy” AQI category. The top 6 most polluted cities in Colorado on Wednesday, August 19 were located in Mesa County, miles from the Pine Gulch fire.

Clifton, six miles east of Grand Junction, registered as the most polluted city in Colorado, on Wednesday, August 19, with air quality levels in the “unhealthy” AQI category. Grizzly Creek: 32,631Acres

Clifton, six miles east of Grand Junction, registered as the most polluted city in Colorado, on Wednesday, August 19, with air quality levels in the “unhealthy” AQI category.

Clifton, six miles east of Grand Junction, registered as the most polluted city in Colorado, on Wednesday, August 19, with air quality levels in the “unhealthy” AQI category. The Grizzly Creek fireconsumed both sides of the Interstate highway, blocking a major roadway across Colorado.

Clifton, six miles east of Grand Junction, registered as the most polluted city in Colorado, on Wednesday, August 19, with air quality levels in the “unhealthy” AQI category. Despite the larger size of the Pine Gulch Fire, the Grizzly Creek Fire near Glenwood Springs was named the “number 1 fire priority in the nation" by Colorado Gov. Jared Polis. The over 30,000-acre fire commanded the state’s attention as it neared both the municipal water supply of Glenwood Springs and the Colorado River watershed, responsible for supplying 40 million Colorado residents.⁹

Clifton, six miles east of Grand Junction, registered as the most polluted city in Colorado, on Wednesday, August 19, with air quality levels in the “unhealthy” AQI category. The Grizzly Creek Fire, which burned on both sides of the state’s vital Interstate-70 highway, was described as a “public works fire” for the significant threat it posed to regional infrastructure. At the time it burned, it was the largest fire in the history of the White River National Forest.

Clifton, six miles east of Grand Junction, registered as the most polluted city in Colorado, on Wednesday, August 19, with air quality levels in the “unhealthy” AQI category. The area’s geography made the Grizzly Creek Fire particularly difficult to contain. Known for its steep canyon walls, firefighters couldn’t employ ground crews in the precipitous Glenwood Canyon. Rather, suppression efforts relied primarily on aerial tactics, such as dropping fire retardant.

Clifton, six miles east of Grand Junction, registered as the most polluted city in Colorado, on Wednesday, August 19, with air quality levels in the “unhealthy” AQI category. The Glenwood Canyon’s famous Colorado River, a popular river rafting destination, may have murky sediment for years to come, as rains slowly carried ashy soil and soot downhill and into the river. The murky waters could make river rafting and fishing activities nonexistent for the foreseeable future.

Clifton, six miles east of Grand Junction, registered as the most polluted city in Colorado, on Wednesday, August 19, with air quality levels in the “unhealthy” AQI category. The Grizzly Creek fire has had well-monitored impacts on the air quality of nearby towns. Aspen’s air pollution levels and Vail’s air pollution levels experienced AQI levels as high as 180. Aspen’s highest daily AQI average was on Monday, August 17, with an AQI average of 152.

Clifton, six miles east of Grand Junction, registered as the most polluted city in Colorado, on Wednesday, August 19, with air quality levels in the “unhealthy” AQI category. By December 18, fire officials had declared the fire 100% contained. Though the Grizzly Creek Fire hadn’t been active for over a month, officials waited until snow had fallen in the uncontained sections of the Grizzly Creek drainage before declaring the fire contained.¹⁰

Clifton, six miles east of Grand Junction, registered as the most polluted city in Colorado, on Wednesday, August 19, with air quality levels in the “unhealthy” AQI category. Cameron Peak: 208,913 Acres¹¹

Clifton, six miles east of Grand Junction, registered as the most polluted city in Colorado, on Wednesday, August 19, with air quality levels in the “unhealthy” AQI category. The Cameron Peak fire, which burned near Rocky Mountain National Park, began on Thursday, August 13, growing to nearly 16,000 acres in a week.¹² Prior to containment, the Cameron Peak fire became the largest fire in Colorado history. 100% containment would not be achieved until December 2.

Clifton, six miles east of Grand Junction, registered as the most polluted city in Colorado, on Wednesday, August 19, with air quality levels in the “unhealthy” AQI category. The fire is expected to have been started by human-activity, as there was no recorded lightning in the area at the time it began.

Clifton, six miles east of Grand Junction, registered as the most polluted city in Colorado, on Wednesday, August 19, with air quality levels in the “unhealthy” AQI category. Firefighters from 46 states and Puerto Rico were brought in to battle the Cameron Peak Fire Preserving the national park and the residents of Estes, Colorado was stated as the first priority for area firefighters. However, high temperatures, challenging terrain, and low humidity combined with drought-impacted trees created a difficult environment for containment.

Clifton, six miles east of Grand Junction, registered as the most polluted city in Colorado, on Wednesday, August 19, with air quality levels in the “unhealthy” AQI category. Emergency evacuations were ordered for Lory State Park as late as October.¹³

Clifton, six miles east of Grand Junction, registered as the most polluted city in Colorado, on Wednesday, August 19, with air quality levels in the “unhealthy” AQI category. Williams Fork: 14,833 Acres¹⁴

Clifton, six miles east of Grand Junction, registered as the most polluted city in Colorado, on Wednesday, August 19, with air quality levels in the “unhealthy” AQI category. The Williams Fork Fire of Grand County was the smallest of the major fires that burned in Colorado during late 2020. It was determined to have started as a result of human activity on August 14, on Byers Mountain.

Clifton, six miles east of Grand Junction, registered as the most polluted city in Colorado, on Wednesday, August 19, with air quality levels in the “unhealthy” AQI category. Mild conditions on Tuesday, August 18, resulted in little growth in the days following the outbreak of the fire. The towns of Winter Park and Fraser were told to be on standby, for notices of evacuation.

The fire was declared controlled on November 27.