Smog and Pollution: What Do Air Quality Alerts Actually Mean?

Most people know that air quality alerts can warn you when air pollution levels rise. But you may not know exactly what they mean — or how they can help you protect your health.

Pulmonologist Sumita Khatri, MD, answers our questions on how the Air Quality Index works, what impact poor air quality has on your health and how you can minimize its effects.

Q: What does the Air Quality Index measure?

A: It measures five pollutants regulated by the Clean Air Act:

• Ground-level ozone
• Particulate matter
• Carbon monoxide
• Sulfur dioxide
• Nitrogen dioxide

Human activity, such as manufacturing and burning fossil fuels for transportation, produces these pollutants. Some are at higher levels during certain times of the year, especially if there are wildfires happening.

“Wildfires cause poor air quality hundreds to even thousands of miles away and weather patterns affect the dispersion of the air pollution,” says Dr. Khatri. “Ozone is generally more of a problem in the summer, while particulate matter is a year-round pollutant.”

Q: What do Air Quality Index numbers mean? 

A: The Air Quality Index rates air quality levels on a scale of 0 to 500. The Environmental Protection Agency (EPA) describes the ratings this way:

• 0 to 50 – Good – Air quality is satisfactory. Air pollution poses little or no risk.
• 51 to 100 – Moderate – Air quality is acceptable. However, some pollutants may pose a moderate health concern for those who are unusually sensitive to air pollution.
• 101 to 150 – Unhealthy for Sensitive Groups – Members of sensitive groups may experience health effects. The general public is not likely affected.
• 151 to 200 – Unhealthy – Everyone may begin to experience health effects. Members of sensitive groups may see more serious health effects.
• 201 to 300 – Very Unhealthy – This triggers a health alert. Everyone may see more serious health effects.
• 301 to 500 – Hazardous – This triggers a health warning of emergency conditions. The entire population is more likely affected.

Dr. Khatri notes that the EPA sets the overall rating according to the pollutant that’s at the highest level at any given time. For example, if the ozone value is 200, the EPA rates the air quality that day at the “unhealthy” level, even if other pollutants are at lower levels.

Q: How can poor air quality impact your health?

A: Poor air quality can make breathing-related conditions worse. This includes conditions such as:

• Asthma
• Allergies
• Chronic obstructive pulmonary disease (COPD)
• Chronic bronchitis
• Emphysema

And, poor air quality affects other people as well. It’s associated with heart attacks, arrhythmia (irregular heart beat) and strokes.

“Even though you’re inhaling the air, it doesn’t just impact your lungs,” Dr. Khatri says. “Pollution can increase inflammation all over the body, and inflammation plays a role in all kinds of illnesses.”

One study found that people walking in high-traffic areas in London had higher levels of inflammation than those walking in a park.

Q: What protective steps can you take?

A: Dr. Khatri recommends that you take the following measures on days when air quality is poor:

• Stay indoors as much as possible. Keep the windows closed, even if it seems nice out. Often you can’t see or smell pollution, even though it’s there.
• Use air conditioning. And when you’re in the car, set the air conditioning to recirculate air rather than draw air in from outside.
• Use a HEPA (high efficiency) filter in your home to trap both particulate matter and allergens. Dr. Khatri advises against using other types of home “air purifiers.” They can create ozone and make indoor air quality worse, she says.
• Try to avoid exercising outdoors at times of day when pollution is high, such as during rush hour.
• If you do exercise outdoors, choose parks and other green spaces rather than congested streets.

Q: Can the average person help improve air quality?

A: Yes. Since the pollutants that cause poor air quality are the result of human activity, you can help by making some changes.

• Pump gasoline during the coolest part of the day. “When the volatile organic compounds from the gasoline start to evaporate, they interact with the sun and the heat and make atmospheric ozone worse,” Dr. Khatri says.
• Watch when you use gas-powered lawn and garden equipment. Try not to use lawnmowers, trimmers and leaf blowers when air quality is poor.
• Switch to electric or battery-operated equipment. Some cities offer rebates to encourage people to trade in gas mowers for electric ones.
• Choose more fuel-efficient ways to get around. Carpooling, bicycling or taking public transportation are all good options.
• Turn your vehicle off if you’re idling for more than 10 seconds. Try this at a drive-through, railroad crossing, or in the school pick-up line, for example.

“You may feel like what you’re doing is just a little drop in the ocean,” says Dr. Khatri. “But these sorts of incremental efforts make a difference.”