What Can the Air Quality Index Tell You?

People view the Manhattan skyline as it continues to sit under a haze on July 21, 2021 in New York City

Spencer Platt / Getty Images

Key Takeaways

  • Wildfire air pollution from the West Coast traveled across the continent, muddling skies in New York and across the East Coast this week.
  • Experts recommend checking the air quality near you by using sites that show an air quality index (AQI).
  • When the air is too polluted, especially with small particulate matter from wildfires, it’s best to stay indoors and limit your activity outdoors. 

When New Yorker Brian Kahn woke up on Tuesday morning, he found a nearby chair to be illuminated in what he described as a “bizarre sort of millennial pink hue.”

After checking the weather forecast, his suspicions were confirmed: smoke from wildfires in western United States and central Canada had reached New York City, filtering the sun’s light and casting a warm hazy glow over the city.

“Not only can you see the smoke, not only can you feel the smoke in your lungs, but you can also actually smell the smoke as well, so it's very low to the ground,” Kahn, MA, a lecturer at the Columbia Climate School and managing editor of Earther tells Verywell. “It's pretty surreal given that this smoke has traveled thousands of miles to be here," he adds.

An aggressive heat wave earlier this month set off at least 78 fires in the West Coast, burning more than a million acres. The ongoing Bootleg Fire in Oregon has already burned an area larger than the city of Los Angeles. And smoke from California’s Dixie Fire has created a plume so large that it’s creating lightning strikes, which could set off new fires.

When wildfire smoke is released into the air, it can be swept up and carried thousands of miles, bringing with it harmful pollutants.

As climate change worsens and conditions in the West remain dry and hot, experts expect that large-scale fires will burn for a greater part of the year. Bigger and larger fires are likely to drive an increase in smoke production which could pollute the air for people far removed from the blaze.

“The locations that are already on fire in a bad way are likely to see fire activity increase in the coming months,” Kahn says. “That doesn't necessarily mean that all the smoke will blow to New York, but I think it's distinctly possible that the conditions out West could lead to more bad air quality across the country.”

How to Understand the Air Quality Index

To evaluate air quality, the Environmental Protection Agency a widely used metric called the Air Quality Index (AQI). It runs from 0 to 500, with 500 being the most polluted.

The metric takes into account five major air pollutants: ground-level ozone, particle pollution, carbon monoxide, sulfur dioxide, and nitrogen dioxide.

Ed Avol, MS, a respiratory health expert and professor of clinical population and public health sciences at the University of Southern California, recommends checking the AQI routinely.

“It's really a composite. It looks at a number of different contaminants that are in the air and gives an average score for all those things," Avol tells Verywell.

PM2.5, or particle matter that is 2.5 micrometers in diameter, is likely the most dangerous output from wildfire smoke. It is more than 30 times smaller than the average human hair.

These tiny particles can make their way through the lungs and sometimes into the blood stream, causing or exacerbating a variety of health problems including lung disease, heart attacks, asthma, stroke, and cancer.

When the AQI is below 100, it’s generally acceptable. Anything above that is deemed unhealthy for sensitive groups, which generally include children, people who are pregnant, people with heart or respiratory conditions, and outdoor laborers with long exposure times, Avol says.

On Tuesday, the AQI in New York City reached 170 and the level of PM2.5 was nine times more than the exposure recommendation from the World Health Organization. New York State issued an air quality health advisory due to the high level of fine particulate matter in the air.

At such levels, PM2.5 can inflame the lungs, causing wheezing, shortness of breath, coughing, runny nose, and sore throat. Persistent exposure to this kind of pollution can cause lasting health problems which sometimes lead to hospitalization.

“There are health issues sort of across the gamut," Avol says. "The clear message ought to be ‘avoid the smoke.'"

What This Means For You

Being exposed to too high concentrations of wildfire smoke pollution can be damaging to your health. When the AQI is above 150, consider staying indoors or avoiding strenuous activity outdoors. To track the air quality in your area, refer to or Purple Air.

Staying Healthy When Air Quality Is Bad

To learn the real-time air quality nearby, you can check your weather app or visit AirNow uses research grade instruments to report an accurate AQI, though the instruments may be spaced too far to give a precise read of the air near you.

Another website, called Purple Air, crowdsources data from air quality monitors in people’s homes. Users report the AQI from inside or outside their homes and the numbers are presented in a multi-colored map that demonstrates air quality with a more nuanced picture.

When the air appears to be heavily polluted, Avol recommends staying inside, keeping the windows and doors shut to block pollution from entering and using an filter to purify the air. When there is a lot of air pollution, it’s also smart to avoid strenuous activity and exercise outdoors.

“We all like to think that we're each immortal or invulnerable, but in fact we are sensitive to this,” Avol says. “Some of these health effects can be a little subtle, because they accrue over time."

2 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Air Quality Index Basics.  

  2. Environmental Protection Agency. Particulate Matter Basics.

By Claire Bugos
Claire Bugos is a health and science reporter and writer and a 2020 National Association of Science Writers travel fellow.