Data provided by
10:07, Aug 8
live AQI index
|Air pollution level||Air quality index||Main pollutant|
|Moderate||52 US AQI||PM2.5|
|Close your windows to avoid dirty outdoor air|
|Sensitive groups should reduce outdoor exercise|
|Wednesday, Aug 5|
Moderate52 US AQI
|Thursday, Aug 6|
Good40 US AQI
|Friday, Aug 7|
Good31 US AQI
Good25 US AQI
|Sunday, Aug 9|
Good36 US AQI
|Monday, Aug 10|
Good41 US AQI
|Tuesday, Aug 11|
Good34 US AQI
|Wednesday, Aug 12|
Good27 US AQI
|Thursday, Aug 13|
Good26 US AQI
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In 2019, Denver averaged a yearly air quality index (AQI) score of 34, meeting the “good” AQI category. Denver air quality, however, fails to meet other attainment standards, such as thresholds for daily PM2.5 and ozone. It is Denver daily pollution swings, particularly in the winter months, that cause Denver to rank among the top 10 worst U.S. cities for hazardous air pollution by various independent studies.1
A federal tally revealed that Denver residents breathed air exceeding government standards for more than 260 days from 2018 to 2019. Air in excess of government standards can affect everyone, though it tends to disproportionately hurt sensitive groups, such as children, the elderly, and those with heart or lung disease. An estimated 338,217 Denver residents qualify as ‘sensitive’ to air pollution, comprising more than 40% of the city’s population.2
According to the State of the Air report, released annually by the American Lung Association, Denver was rated an ‘F’ for experiencing too many unhealthy ozone days (in excess of the federal standard for 3.2 days). Breathing ozone can cause breathing trouble, chest pain, coughing, and airway inflammation. It can be particularly troubling to those with asthma or other respiratory illnesses, at times requiring medical care.
Normally, pollution levels in Denver are higher in the winter months than in the summer months as a result of temperature inversions. Temperature inversions are weather events in which cold, polluted air near the ground is unable to escape into the atmosphere and disperse because of a layer of hotter air above, which creates a trapping effect. In the winter, weakened sunlight and a frozen ground combine to create temperature inversions, sometimes lasting days at a time.
In 2019, Denver’s most polluted months for PM2.5 pollution were February (14.7 μg/m3), March (11.8 μg/m3), November (11.2 μg/m3), and December (9.8 μg/m3), respectively. While this trend remains true for previous years such as 2018 and 2017, the single most polluted month for these years was in the summer because of from nearby wildfires. August was the most polluted month in 2018 (13.6 μg/m3), while September was the most polluted month in 2017 (11.2 μg/m3).
Despite Denver’s challenges with air pollution, the city is not the most polluted in Colorado. In 2019, Silverton was Colorado’s most polluted city (affected by wildfires in 2019), followed by Greeley (a city known for its meatpacking industry).
Air pollution is dynamic, changing with seasons, weather, and pollution events. Follow Denver live air quality data at the top of this page and on the IQAir app for real-time readings. Denver forecast air quality data provides a guideline for planning ahead to reduce pollution exposure. When pollution levels are estimated to be high, close your windows and doors, wear a pollution mask, and avoid heavy physical exertion.
Air pollution levels in Denver have improved since the 1980s, when the city was reputed for its “brown cloud”.3 In the last two decades, progress has slowed significantly, only meandering towards progress with numerous off trend years as well.
Most recently, PM2.5 pollution levels have been on the rise, gaining 8.1% from 2017 to 2018, and another 2.5% from 2018 to 2019.
Ozone levels have similarly experienced slight increases in recent years, with levels remaining constant between 2017 and 2018 but increasing to non-attainment levels in 2019.1
While increased public transportation, a greater share of electric vehicles on the road, and further regulations on the oil and gas industry present opportunities for reducing air pollution levels in Denver, global warming is expected to intensify the problem. Heat speeds the formation of ozone by providing longer periods of ideal conditions. Rising temperatures may also contribute to the increased frequency and severity of wildfires which have historically given rise to some of Denver’s most polluted months. Wildfires are a major source of fine airborne particulate matter (PM2.5) as well as ozone precursors and can have far reaching implications on air quality.
Denver’s air quality is primarily challenged by ozone pollution formed from precursor pollutants emitted by motor vehicles (mobile sources) and the oil and gas industry (stationary sources). Studies have shown that these two sources play a near equal role in polluting Denver’s air.
Transportation, or mobile, emissions from trucks, trains, planes, and all other motor vehicles comprise the largest single contributor to Denver’s air pollution. In April 2020, the city and county of Denver released a new electric vehicle action plan aiming to further incentive electric vehicles ownership in order to grow their share of vehicle registrations to 15% by 2025 and 30% by 2030.4 Ongoing projects to expand public transportation and bike lanes to make these offerings more attractive offer additional avenues for reducing mobile emission sources in the future.
The oil and gas industries are frequently grouped into the ‘stationary sources’ of pollution category, which additionally includes emissions from power plants, industrial facilities, and factories. The Suncor Energy Oil Refinery in Commerce City, just miles outside of Denver, is the state’s second-largest stationary source of PM2.5 and the fourth-largest source of volatile organic compounds (a precursor pollutant in the formation of ozone), thought to significantly contribute to Denver’s poor air quality.5
New oil drilling near Denver, meanwhile, is on the rise, with new fracking projects currently underway in nearby Thornton, Commerce city and Aurora, and nearly 1,000 new projects pending approval.6 These projects have the potential to further worsen to Denver’s air quality, as they are known to emit significant amounts of ozone and PM2.5 precursor pollutants.
Operations at the Denver International Airport (DIA) are another stationary source of Denver air pollution. Emissions here are primarily the result of ground operations rather than airplanes. According to data from the Environmental Protection Agency (EPA), DIA is one of the main contributors of Denver’s ozone precursor pollutants, volatile organic compounds, and nitrogen oxides.
Wildfires, though unpredictable and temporary, are another common source of air pollution in Denver, frequently contributing to Denver’s highest pollution days. A combination of dry air, abundant forest land, increasingly hot summers, and steep mountains combine to make Western Colorado particularly prone to these severe pollution events.
View real-time data on the Denver AQI map to observe the impact of emission sources and wind patterns on air quality levels.
+ Article Resources
 Finley B. (2020, January 30). Denver among top 10 worst U.S. cities for hazardous air pollution, 2 new studies say.
 American Lung Association. (2019). State of the air – 2019.
 Brooke J. (1998, April 21). Denver Seeing the Light Past Its 'Brown Cloud'.
 Denver Climate Action, Sustainability and Resiliency. (2020). Denver electric vehicle (EV) action plan.
 Woodruff C. (2019, May 29). What are Colorado’s biggest sources of air pollution?
 Woodruff C. (2019, March 11). Why Denver’s brown cloud Is back — and why it might get worse.