By Marnie Kunz

Does running in bad air quality hurt your health? If you have an air quality alert in your area, you may be wondering if it’s ok to run. Recently in NYC, we experienced the worst air quality days in the city’s monitoring history and were dealing with questions about what’s safe and when to stay inside. As officials warned people not to exercise outdoors, the question hung in the air - when would it be safe to run outside again, and what measure lets us know?

In this article, we’ll explore what running in bad air quality entails, how air quality is measured, safe air quality for running, and the effects of air quality on your running and health. We’ll also go over general guidelines using Air Quality Index (AQI) so you can figure out when it’s safe to run outside. Knowing when it’s ok to run outside and when to exercise indoors can help you stay safe and avoid long-term risks to your heart and lungs.

What is Bad Air Quality? AQI

Bad air quality is a general term that refers to a range of air quality levels. Air Quality Index or AQI is a tool governments use to demonstrate the air quality level. The AQI scale ranges from 0 to 500, with 0 being the absolute best and 500 the worst. Five main measurements go into determining AQI, which include:

ground-level ozone
particle pollution (also known as particulate matter, including PM2.5 and PM10)
carbon monoxide
sulfur dioxide
nitrogen dioxide

AQI Ratings

The AQI has six categories rating the air quality, with a different color for each category. The categories are:

Green air quality rating is the best and includes scores of 0 to 50. Air pollution is very low at this level, and the air should be safe for everyone to run outdoors.
Yellow is a moderate air quality rating, with a score of 51 to 100. This rating is deemed “acceptable” to most people, except for people unusually sensitive to air quality. For most people, you can run outdoors on yellow air quality days. However, if you have asthma, heart or lung issues, or are a senior, it may be better to run inside on a treadmill on yellow air quality days.
Orange air quality between 101 and 150 is unhealthy for vulnerable groups such as people with heart and lung conditions, asthma, and older people. These groups should exercise indoors. Other runners may be ok to run outside. Still, the long-term effects of running on orange air quality days can accumulate over time. Try lower intensity exercise such as walking.
Red air ranks between 151 to 200. Red air quality days are unhealthy to some people in the general population and hazardous to sensitive groups. Do not exercise outdoors on red air quality days.
Purple days have an AQI between 201 and 300. This is a very high level of pollutants, and the air is very unhealthy for everyone. Health issues increase for all groups, and staying indoors for your workouts is best.
Maroon air quality is the worst, ranging from 301 to 500. These are extremely unhealthy conditions. Everyone is likely to be affected and should stay indoors.

What Causes Bad Air Quality?

As you can see from the AQI categories, running in bad air quality is a risky situation. Various factors, including pollution and natural disasters like wildfires, can cause poor air quality. Gas-powered vehicles, carbon emissions, and rising ozone levels often cause polluted air.

Smoke from wildfires, which was the cause of the dangerous air quality in NYC, can also cause hazardous breathing conditions. Smoke contains carbon monoxide and other harmful chemicals. Climate change causes increased dry, warm conditions, contributing to a spike in wildfires and poor air quality.

Running in Bad Air Quality

Running in bad air quality can pose health risks, with more risks the higher the AQI rating. Knowing when it’s safe to run outside is essential as the air quality worsens. Generally, it's best to exercise indoors if the AQI is orange or worse, rated above 100. For vulnerable people, including pregnant women, people with asthma, lung or heart conditions, and seniors, exercising indoors is also best for moderate air quality days (with an AQI of 51 to 100).

According to the American Lung Association, more than 4 in 10 Americans, or over 135 million people, live in places with unhealthy ozone levels or particle pollution. Particle pollution can cause heart and lung conditions, worsen existing heart or lung conditions, and cause premature death, according to the American Lung Association. Ozone gas irritates the lining of the lungs, causing inflammation and decreased lung functioning. Even young, healthy people experience difficulty breathing, chest tightness, and shortness of breath from unhealthy ozone levels. Long-term exposure to harmful ozone levels can cause respiratory infections like pneumonia, asthma, metabolic disorders, central nervous system damage, and chronic obstructive pulmonary disease (COPD).

Although there have not been a lot of studies on the long-term effects of running in bad air quality, the European Heart Journal published a study about the benefits and hazards of running outside in different air quality conditions. According to the study, young adults who exercised outdoors on low to moderate air quality days reaped the health benefits of decreased risk of cardiovascular disease. But young adults who exercised in areas with high particle pollution levels were adversely affected. In other words, the health risks from exposure to pollution while outdoors outweighed the health benefits of exercising.

Air Quality Guidelines for Running Outside

To avoid running in bad air quality and the associated health risks, here are some general guidelines:

Know the AQI in Your Area

You can check the AQI in most weather apps or download the IQAir app for the most updated air quality information based on air measuring stations in your area. The app has helpful tips and guidelines based on your AQI rating.

If you are not in a vulnerable group, you should be able to run outside on green and yellow air quality days - when the AQI is 100 or less. If you’re in a sensitive group or are especially worried about air pollution, if the AQI is 51 or above (yellow or worse), then exercise indoors.

Adapt Your Workouts

When air quality is poor, take your workouts inside. You can hit the treadmill or do some strength training exercises. Although it can be frustrating when it’s too polluted to run outside, it’s better to take care of your long-term health and ensure you enjoy many more miles ahead by staying inside.

If the air quality is yellow or orange, you may be able to exercise with precautions. By lowering the intensity of your exercise, for instance, you will reduce your inhalation of pollutants. This may mean walking instead of running to get in your daily steps or wearing a filtration mask on your walk if the air quality is above 100.

If it’s especially hot and humid outside, this intensifies air pollution. Avoid exercising outdoors during peak heat times and in direct sunlight. Do your workouts early in the morning or the evening when the temperatures cool. Ozone levels are usually best in the early mornings so this is an ideal time to exercise. See our 20 Tips for Running in Heat and Humidity for more help with hot weather.

Also, running near traffic can increase the pollutants you inhale. On days with moderate air quality, head to a park or other tree-lined space with little traffic to give yourself the best air. Avoid running by congested highways and roadways, and if you can, run before or after rush hours.

Hopefully, this post helps you avoid running in bad air quality so you enjoy many healthy miles ahead. Happy - and healthy - running to you!

If you need a training plan to crush your next race, head to the Runstreet Training Center so I can help.

Resources: IQAir app

Marnie Kunz is a NASM-certified trainer and USATF- and RRCA-certified running coach based in Brooklyn, a dog lover and Akita mom, and the founder of Runstreet.

Running in Bad Air Quality: When Is It Safe to Run?