Air Quality 

Index 

Who Needs to 

be Concerned? What Should I Do?

Good

(0-50) It’s a great day to be active outside.

Moderate

(51-100)

Some people who may be unusually sensitive to ozone.Unusually sensitive people: Consider reducing prolonged 

or heavy outdoor exertion. Watch for symptoms such as 

coughing or shortness of breath. These are signs to take it 

easier.

Everyone else: It’s a good day to be active outside.

Unhealthy for 

Sensitive Groups

(101-150)

Sensitive groups include

people with lung disease 

such as asthma, older adults, 

children and teenagers, and 

people who are active outdoors.

Sensitive groups: Reduce prolonged or heavy outdoor exertion. Take more breaks, do less intense activities. Watch for 

symptoms such as coughing or shortness of breath. Schedule outdoor activities in the morning when ozone is lower. 

People with asthma should follow their asthma action 

plans and keep quick- relief medicine handy.

Unhealthy

(151-200)

Everyone Sensitive groups: Avoid prolonged or heavy outdoor exertion. Schedule outdoor activities in the morning when ozone 

is lower. Consider moving activities indoors. People with 

asthma, keep quick-relief medicine handy. 

Everyone else: Reduce prolonged or heavy outdoor exertion. Take more breaks, do less intense activities. Schedule 

outdoor activities in the morning when ozone is lower. 

Very Unhealthy 

(201-300)

Everyone Sensitive groups: Avoid all physical activity outdoors. Move 

activities indoors or reschedule to a time when air quality 

is better. People with asthma, keep quick-relief medicine 

handy. 

Everyone else: Avoid prolonged or heavy outdoor exertion. 

Schedule outdoor activities in the morning when ozone is 

lower. Consider moving activities indoors. 

Hazardous 

(301-500)

Everyone Everyone: Avoid all physical activity outdoors.

Air Quality Guide for Ozone

Ground-level ozone is one of our nation’s most common air pollutants. Use the chart below to help reduce your 

exposure and protect your health. For your local air quality, visit www.airnow.gov

Note: If you don't have an air conditioner, staying inside with the windows closed may be dangerous in extremely hot 

weather. In these cases, seek alternative shelter.
What is ozone?

Ozone is a colorless gas that can be good or bad, 

depending on where it is. Ozone in the stratosphere 

is good because it shields the earth from the sun’s 

ultraviolet rays. Ozone at ground level, where we breathe, 

is bad because it can harm human health.

Ozone forms when two types of pollutants (VOCs and 

NOx) react in sunlight. These pollutants come from 

sources such as vehicles, industries, power plants, and 

products such as solvents and paints. 

Why is ozone a problem?

Ozone can cause a number of health problems, including 

coughing, breathing difficulty, and lung damage. 

Exposure to ozone can make the lungs more susceptible 

to infection, aggravate lung diseases, increase the 

frequency of asthma attacks, and increase the risk of early 

death from heart or lung disease. 

Do I need to be concerned?

Even healthy adults can experience ozone’s harmful 

effects, but some people may be at greater risk. They 

include:

•	 People with lung disease such as asthma

•	 Children, including teenagers, because their lungs 

are still developing and they breathe more air per 

pound of body weight than adults

•	 Older adults 

•	 People who are active outdoors, including outdoor 

workers

How can I protect myself?

Use the Air Quality Index (AQI) to plan outdoor activities. 

To keep the AQI handy, sign up for EnviroFlash emails, get 

the free AirNow app, or install the free widget on your 

website. Find all of these tools at www.airnow.gov.

Stay healthy: exercise, eat a balanced diet, and keep 

asthma under control with your asthma action plan.

When you see that the AQI is unhealthy, take simple steps 

to reduce your exposure:

•	 Choose a less-strenuous activity

•	 Take more breaks during outdoor activity

•	 Reschedule activities to the morning or to 

another day

•	 Move your activity inside where ozone levels are 

usually lower

Can I help reduce ozone? 

Yes! Here are a few tips. 

•	 Turn off lights you are not using

•	 Drive less: carpool, use public transportation, bike 

or walk 

•	 Keep your engine tuned, and don’t let your 

engine idle

•	 When refueling: stop when the pump shuts off, 

avoid spilling fuel, and tighten your gas cap

•	 Inflate tires to the recommended pressure

•	 Use low-VOC paint and cleaning products, and seal 

and store them so they can’t evaporate

•	 Watch for Air Quality Action Days in your area

Key Facts to Know About Ozone:

•	 Ozone in the air we breathe can cause serious health problems, including breathing difficulty, asthma attacks, 

lung damage, and early death.

•	 Ozone forms in the sun, usually on hot summer days. Ozone is worse in the afternoon and early evening, so plan 

outdoor activities for the morning.

•	 You can reduce your exposure to ozone and still get exercise! Use the Air Quality Index (AQI) at www.airnow.gov to 

plan your activity.

Office of Air Quality and Radiation 

EPA-456/F-15-006

www.airnow.gov

August 2015