Air quality in Colorado

Air quality index (AQI) and PM2.5 air pollution in Colorado

Last update at (local time)


Real-time Colorado
Most polluted city ranking

#cityUS AQI
1The national flag of International Florence


2The national flag of International Welby


3The national flag of International Greeley


4The national flag of International New Castle


5The national flag of International Gothic


6The national flag of International Aspen


7The national flag of International Mancos


8The national flag of International Castle Rock


9The national flag of International Cortez


10The national flag of International Towaoc


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Real-time Colorado
Cleanest city ranking

#cityUS AQI
1The national flag of International Conifer


2The national flag of International Silverton


3The national flag of International Bayfield


4The national flag of International Collbran


5The national flag of International Columbine Valley


6The national flag of International Creede


7The national flag of International San Luis


8The national flag of International Burlington


9The national flag of International Hayden


10The national flag of International Telluride


(local time)


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Is Colorado a state with polluted air?

Colorado is a state in the Mountain West region of the United States. It comprises of most of the Southern Rocky Mountains as well as the north eastern section of the Colorado Plateau and the western area of the Great Plains. The estimated 2020 population of Colorado is 5.8 million which is an increase of 15.5 per cent since the 2010 United States Census. It shares a land border with 7 other states. has just released the latest figures showing the air quality for 2020. Its capital city, Denver achieved the WHO target figure for acceptable air quality with an average reading of 8.7 µg/m³. It attained the target of being 10 µg/m³ or less, for 9 months of the year, only in August, September and October was it higher with readings between 12.1 and 34.5 µg/m³, which classified it as being in the “Moderate” category. This is all in accordance with recommendations from the World Health Organisation (WHO).

Looking back at figures from 2017 onwards, it can be seen that the air quality is in slight decline. A figure of 7.4 µg/m³ was attained in 2017 followed by 8 µg/m³ in 2018. 2019 brought an 8.2 µg/m³ reading followed by the 2020 figure of 8.7 µg/m³.

How is the air quality in Colorado measured?

Air monitoring stations around the state measure the levels of different pollutants. At present, Colorado is reporting real-time measurements of carbon monoxide (CO), nitrogen oxides (NOx), sulphur dioxide (SO2), ground-level ozone (O3) and particulate matter (PM), both PM10 (particles 10 micrometres and smaller) and PM2.5 (particles 2.5 micrometres and smaller).

The two air pollutants that cause the most problems and are considered as the standard that all other pollutants are judged by are ground-level ozone and PM2.5.

Ground-level ozone is the major component in what is also called smog. It is measured continuously by air monitoring stations.

Particulate matter known as PM2.5 includes very small particles of dust, dirt, smoke, soot and even tiny drops of liquid. It is called PM2.5 because these particles are between 0.01 and 2.5 micrometres in diameter. Air monitors measure PM2.5 hourly in some areas, and either daily or once every third day in other areas, depending on the level of concentration.

What are the sources of air pollution in Colorado?

There are many sources of air pollution in Colorado, but the main ones are thought to be from factories, vehicles, buildings, homes and fossil fuel power generators.

One of the largest operators of several power plants committed to extending their use of sustainable energy from both solar and wind power and have disclosed their intention to shut down two of the largest power units in Pueblo, Colorado before 2025.

Greenhouse gases such as carbon dioxide, nitrous oxide, methane, chlorofluorocarbons and hydrofluorocarbons account for the largest proportion of Colorado’s air pollution which is estimated at 125 million tons per year.

There’s no current state limit on greenhouse gas pollution. Companies emitting more than 25,000 tons a year are required, under federal law, to measure and report what they release into the atmosphere. However, in 2019 lawmakers began to set limits which ordered greenhouse gases to be cut to 62 million tons before 2030 and cut again to 13 million tons before 2050.

It is known that 200,000 tons of nitrogen oxides and volatile organic compounds, or VOCs are released into the atmosphere annually. These then react with each other under ultraviolet light producing ground-level ozone. Colorado is one of America’s worst culprits for ozone pollution now.

Can the quality of air in Colorado be improved?

Some sources of pollution are out of the control of any state, such as the local topography and the ingress of ozone from neighbouring areas, but recently, emissions that can be controlled through human effort have declined. It is thought that this is mainly due to the modern advancements in automobile manufacture and the use of new technology.

Newer gas-powered vehicles run much cleaner today with passenger vehicles that “are 98 to 99 per cent cleaner for most exhaust pollutants compared to the 1960s. The dealers’ organisation focuses on its Clear the Air Foundation, which has taken 4,000 older vehicles off the roads since its 2011 launch.

Oil companies no longer allow methane to leak into the atmosphere as they used to do, instead, they must seal the pipe to stop it from leaking. Many refineries have to capture their emissions and “clean” the residual gases.

Consumer items such as paint, shoe polish and even lipstick (If it has a scent, it probably contains VOCs) are being looked at by the council to see if existing water-based alternatives could replace the aromatic products sold in Colorado.

What can be done to lessen the risk of poor air quality in Colorado?

Legislation is being considered which would mean Colorado drivers would begin paying a new fee of 2 cents on every gallon of gasoline they purchase starting in July 2022. If approved, the figure will increase to 8 cents per gallon in July 2028. It is part of a $4 billion, 11-year effort to raise and spend money for badly needed transportation projects across the state. It aims to reduce traffic congestion on Colorado’s roads, expand public transportation and improve air quality by making it easier for people to purchase electric vehicles and spending millions on environmental initiatives. A similar charge will be levied on diesel fuel within a similar timeframe.

Charges will also be made against delivery companies such as Amazon and FedEx (25c per delivery has been suggested). The ride-hailing companies will also be subject to a fixed “one-off” charge per journey (30c per trip).

The proposals for the way the money will be spent are:

  • expanding electric-vehicle charging infrastructure
  • fleet-electrification incentives to be distributed by the state health department
  • supporting the electrification of public transport
  • reduce congestion in the cities through traffic-flow improvements

Is Colorado adopting stricter air pollution standards?

In December 2020, the Colorado Air Quality Control Commission finalised a new set of emissions rules aimed at bringing the Denver metro area into compliance with federal ozone pollution standards. Ozone concentrations in and around Denver this year repeatedly exceeded an eight-hour average of 80 parts per billion, above the EPA standard of 75 ppb set in 2008 and well above the revised 2015 standard of 70 ppb.

For decades, Denver has contended with high summertime concentrations of ozone, a hazardous pollutant that forms as a result of a chemical reaction between sunlight and volatile organic compounds. Studies have shown that oil and gas operations and vehicle exhaust emissions are the area’s largest sources of ozone precursors. Industry groups also argue that high levels of “background” ozone in the atmosphere, which can originate from as far away as China, make it difficult to address the problem through local pollution controls alone.

Presently, Denver is the 8th most polluted city in the US, and the entire metro region suffers from severe ongoing ozone pollution.

What are the consequences of breathing in polluted air in Colorado?

Air pollution is especially harmful to people who have a pre-existing lung condition, such as asthma or chronic obstructive pulmonary disease (COPD). Older people, children under the age of 14 years and babies also have a higher risk of experiencing symptoms and other harmful effects from breathing in polluted air. Children tend to be more active than adults and therefore breathe more quickly. Their bodies are also at a lower height which puts them closer to the source of polluted air, vehicle exhausts!

Healthy people who work or exercise outdoors might experience symptoms when they’re exposed to moderate or high levels of pollution. They may feel out of breath or start coughing.

Inhaling any type of smoke is harmful, so it’s best to avoid breathing in bonfire smoke or smoke from other sources. Smoke from burning a range of materials can irritate your airways, your skin and eyes. Breathing in smoke can make you cough or wheeze, feel breathless or produce more phlegm or have pains in your chest. Tiny particles in smoke can also pass deep into the lungs and into your bloodstream increasing the risk of heart attacks and strokes.

When is the air pollution at its worst in Colorado?

When the weather is cold, exhaust from vehicles and chimneys is more visible. While industrial emissions remain mostly constant throughout the year, particulate matter and carbon monoxide pollutants from wood-burning increases during the colder winter months. Idling cars to defrost or keep them warm increases the amount of air pollution as well.

Typically warm, rising air near the ground lifts pollution away, but during the winter the layer of warm air acts like a cap keeping cold air near the surface. This creates a thermal inversion, which forms when a layer of warm air above traps cool air and pollution close to the ground. Thermal inversions are more common above cities where cold air gets trapped in mountain basins or valleys, such as Los Angeles, Denver, and Mexico City.

Ground-level ozone is produced more efficiently in sunny, hot weather. The chemical reactions that create harmful ozone in our atmosphere require sunlight. During summer and especially during extreme heatwaves, ozone often reaches dangerous levels in cities and nearby rural areas.

Colorado air quality data attribution


Which is the most polluted city in Colorado?

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