Running In Bad Air Quality: What AQI is safe for running?

We explain how to check the Air Quality Index in your area, and when it's best to skip your outdoors workout.

In addition to the fact that they keep us alive, our lungs are pretty important when we are running, so taking good care of them is a top priority.

Most athletes don’t smoke or inhale anything suspect, but what about breathing in things that we don’t have control of?

It’s been proven that running in bad air quality can harm your health and affect your running performance, so keep scrolling to find out at what point air pollution makes it unsafe to run, and how you can minimize the effects of polluted air when exercising.

Take a deep breath, and let’s get stuck in!

A runner in a mask for bad air quality, with a forest and power plants in the background.
Credit: Marathon Handbook Staff

What Is AQI?

Air Quality Index or AQI is a measure of air quality.

Once air pollution reaches unhealthy AQI levels, then running outside can be bad for you.

How Do I Find Out What The AQI Of My Area Is?

If you Google search air quality and the name of your town, city, or region, you will likely find recent data on your local air quality.

World AQI and IQAir are both useful sources for finding AQI data.

Purple Air is also a great source, and Air Now is even more accurate, as it uses data staight from the EPA (but only works for those based in the US).

For some other AQI-monitoring apps, check out the following:

  • IQAir AirVisuals
  • Air Matters
  • Plume Labs
  • AirLief

What AQI Is Safe For Running?

In general, regardless of whether you are exercising or not, any rating above Green on the AQI (Air Quality Index) scale is considered unhealthy, meaning the air quality could adversely affect your body over time, including the health of your heart and lungs.

An AQI rating below 50, classified as green or good, is perfectly safe to run in.

An AQI between 51-100 is OK for most people who are healthy to run in, however, over time it could become unhealthy. This is especially true for sensitive individuals. This AQI of category of 51-100 is considered moderately polluted or yellow.

Any other reading over 100 is unhealthy and should be avoided. Past this point, all individuals have a risk of breathing problems whilst exercising outdoors, and sensitive individuals should definitely exercise indoors.

Exercising outdoors with an AQI of greater than 150 is strictly not recommended as there is a high risk of negative health effects.

an image of A man and woman running on a road in the forest

What Are The Health Effects Of Running Outside in Bad Air Quality?

Running in dangerous levels of air pollution can make you sick, and public health institutions recommend against it.

If you do go out running in bad air quality and ignore the signs, as well as potentially harming yourself long-term, you may experience short-term health problems such as shortness of breath and irritation to your eyes and throat.

Furthermore, as outlined below, outdoor exercise in high levels of pollution can also increase your risk of cardiovascular disease and lung diseases such as chronic obstructive pulmonary disease.1NHS. (2019, September 20). Chronic Obstructive Pulmonary Disease (COPD). NHS. https://www.nhs.uk/conditions/chronic-obstructive-pulmonary-disease-copd/

Ozone pollution, also known as smog, is another dangerous form of air pollution and can cause lung inflammation, reduce the ability of the body to transport oxygen, increase the risk of developing respiratory illnesses, and more.2American Lung Association. (2022). Health Impact of Pollution | State of the Air. Www.lung.org. https://www.lung.org/research/sota/health-risks

Does Air Pollution Affect Running Performance?

Air pollution can affect running performance by making it more difficult to breathe.

This is because pollutants can cause swelling in the lungs which increases mucus production and reduces oxygen uptake.

Do The Positive Health Benefits Of Exercise Outweigh The Negative Health Impacts Of Pollution?

When running, your breathing rate increases from around 15 litres of air per minute to 100 litres or more per minute. This means you are likely taking in more pollutants per minute spent exercising than if you were just walking or standing outside.

But does this mean it’s better not to exercise outdoors when there is air pollution? Well, it depends on the level of pollution.

A study from the European Heart Journal showed that people living in low to moderate levels of air pollution who decreased their level of activity increased their risk of getting Cardiovascular Disease (CVD).3Kim, S. R., Choi, S., Kim, K., Chang, J., Kim, S. M., Cho, Y., Oh, Y. H., Lee, G., Son, J. S., Kim, K. H., & Park, S. M. (2021). Association of the combined effects of air pollution and changes in physical activity with cardiovascular disease in young adults. European Heart Journal42(25), 2487–2497. https://doi.org/10.1093/eurheartj/ehab139

When this same group increased their level of physical activity, they decreased their risk of CVD. This showed that the positive impact of exercising outweighed the risk of breathing in the low to moderate levels of air pollution.

However, once air pollution increases beyond this moderate level, increased physical activity also increases your risk of CVD, so the risk of breathing in harmful particles outweighs the benefits of exercise.

The same goes when decreasing your level of physical activity; your risk of CVD also increases.

The conclusion? – If air pollution is above AQI 100, then the negative effects of the pollution may outweigh the positive effects of running on your cardiovascular health.

However, it should be worth noting that all individuals are different, and sensitive individuals, or elderly or children, are more likely to experience enhanced negative health effects of pollution even at lower AQI levels.

Can I Exercise Outside When It’s Smoky?

If there are wildfires close by, it is not recommended to run outside when it is smoky.

In addition to the aforementioned negative health effects of running in air pollution, the smoke from fires is filled with particulates from anything that has been burned by the fire, which could mean breathing in additional toxic chemicals.4Why wildfire smoke is bad for your health. (2023, June 2). Washington Post. https://www.washingtonpost.com/weather/2023/wildfire-smoke-air-quality-health-exposure/

Is It Safe To Exercise Indoors When Air Quality Is Bad?

Running indoors can be an effective way of keeping fit safely whilst there is pollution outside. However, use common sense, and try not to keep windows and doors wide open.

The simplest solution is to use a treadmill.

If you don’t have a treadmill, you can use a local gym. Going to the gym to run might not seem like your cup of tea, but it can be a great experience, and you might even meet a fellow runner or two that you wouldn’t have met otherwise.

How Can I Protect Myself When Running In Bad Air Quality?

If you decide to exercise in bad air quality, you can lower the health risks by running at a lower intensity, thereby reducing your breathing rate and breathing in fewer pollutants than exercising at a higher intensity.

If it’s comfortable, you could also consider wearing an N-95 face mask while you exercise, as they can significantly protect you against particulate-based pollutants.

How To Avoid Running In Bad Air Quality

#1 Avoid Where The Cars Are

Cars and other vehicles are a huge contributing factor to poor air quality. Even if the air quality is good, it is a great idea to avoid congested areas.

This is especially true for rush hour traffic.

Therefore, you should avoid running down busy roads and avoid peak traffic times to avoid running in poor air quality.

If you cannot escape to quieter side roads and you live in the middle of a large city, stay out of the busiest and most tightly built-up areas.

If you are surrounded by tall, closely packed buildings, it is often hard for fresh air to ‘fill’ the space around you, and all the harmful fumes get trapped. So, to avoid running in bad air quality, try to find the most open space you can for training in.

a man running along a trail

#2 Run In Wooded Areas Or Parks

Areas in nature are likely to have fewer cars, and pollution is less likely to get trapped between buildings.

Therefore, running in parks or on trails is a much healthier experience for your lungs.

Often, while running off the beaten track, you might even stumble across photo-worthy sights and new routes to follow.

If you don’t have any green spaces close by, consider travelling further to areas of nature for some exercise in the clean air – your mind will certainly thank you for getting away from the city also.

Whether it’s indoors or out in nature, there’s always a way to get your run in no matter what the circumstances.

What Causes Bad Air Quality?

Air pollution is caused by certain particles of solids or liquids that are suspended in the air. A lot of these harmful particles are due to the burning of fossil fuels as well as forest fires, dust, and a host of other elements.

The build-up of this particulate matter worsens air quality, and it can become harmful as you breathe it in.

Does Temperature Affect AQI?

Both extremely high and extremely low temperatures can amplify air pollution.

Heat and humidity can worsen air quality and increase the likelihood of smog5Talk, permission of the editors of E. our editorial process E. (n.d.). What Affect Do Heat Waves Have on Air Quality? ThoughtCo. https://www.thoughtco.com/heat-waves-make-air-quality-worse-1204013.

This is because during heat waves and other hotter climates, the air essentially ‘cooks’ and forms a thick smog of harmful chemicals. The nitrous oxide in the air from emissions combines with other chemicals in the air and becomes more unhealthy.

On the other end of the scale, during cold winters, AQI can worsen for two reasons. Firstly, people tend to burn more fossil fuels and wood to warm themselves, their homes and their cars, with these increased emissions leading to more harmful AQI readings.

Secondly, in cold air, emissions tend to get trapped at ground level in a process known as temperature inversion.6Cool, dry conditions favour high pollution levels: your CAMS guide to winter’s air quality issues | Copernicus. (n.d.). Atmosphere.copernicus.eu. https://atmosphere.copernicus.eu/cool-dry-conditions-favour-high-pollution-levels-your-cams-guide-winters-air-quality-issues Hotter air sits above the colder air at ground level and acts like a cap keeping the cold air from dissipating.

Hence, in polluted areas, particularly during heatwaves, you should try and run indoors to avoid the heightened level of pollution.

What Do The AQI Categories Mean?

Air Quality Index or AQI is a measurement from 0-500. The higher the number, the more potentially harmful the air quality is to you.

This is broken into 6 main sections from Green for low air pollution up to Maroon, the highest level of air pollution. This makes it easier to understand at a glance.

The term sensitive individuals includes those with asthma and other heart and lung conditions.

AQI Categories Explained

  • Green: Good. 0-50. Good means it is perfectly safe to exercise outdoors.
  • Yellow: Moderate. 51-100. A rating under 100 is still safe to do outdoor activities and exercise. If you are sensitive to the pollutants in the air then your breathing may be affected, but for non-sensitive individuals, you are ok.
  • Orange: Unhealthy for sensitive groups. 101-150. Healthy people may not be affected during everyday life, however, when exercising, all people may experience breathing problems while out running. Sensitive individuals should avoid running outdoors and exercise inside.
  • Red: Unhealthy. 151-200. Everyone’s breathing will be affected by the pollution in the air, so exercise inside to avoid being exposed for prolonged periods.
  • Purple: Very Unhealthy. 201-300. Very unhealthy to run outside, so stay indoors. The level of pollution can lead to serious health problems for all individuals.
  • Maroon: Hazardous. 301-500. Do not go outside and keep looking at local advice on what to do next. And maybe think about running on a different day...


Photo of author
Tom McMeekin-Donnelly is a runner, outdoor enthusiast and cyclist. Tom competes in ultra-marathons in the UK and Ireland. Tom runs anything from a marathon to 100 miles. He can often be found in the mountains around his home in Ireland.

3 thoughts on “Running In Bad Air Quality: What AQI is safe for running?”

  1. Nice article! Researching because AQI is “unhealthy” this morning. Will use the treadmill. BTW, running in the sun is discouraged if an unhealthy AQI includes high NO2, the sunlight converts NO2 into ozone, another unhealthy component.

  2. it is highly advisable to not run at all when the AQI is over 150 (unhealthy for sensitive groups and poor Air Quality for all). I have experienced such conditions numerous times and cancelled runs, events where I was located, or I have run or exercised indoors with a HEPA filter in action. Sometimes I have been working an aid station and the Air Quality became poor or worse – I usually will have an N95 face mask with me to wear in such cases, but see many running and starting 50k’s when the Air Quality is poor or worse.
    While you might not feel the effects of such smoke (and very fine particulate matter and other carcinogens) for some time, it may impact you many years or decades later.

    Tough decisions, but people need to be aware of the conditions and what it can mean to you! Although an engineer, I practiced Air Quality (AQ) and other environmental fields (primarily AQ) for 35 years. Unfortunately these years we have had so many more wildfires and poor AQ days or weeks (wintertime as well) so always pay attention to the AQ in your area!


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