What is an Air Quality Index and what does it mean for people smelling smoke in NC?
As wildfire smoke from Canada drifts over North Carolina, people are becoming reacquainted with the Air Quality Index, what it measures and what it means for their lives.
In North Carolina, the N.C. Division of Air Quality, or DAQ, measures pollution like ozone and PM2.5, or particulate matter that is much smaller than the width of a human air. Air quality meteorologists also model how weather patterns could affect upcoming pollution and use those models to issue warnings when they are appropriate.
The warnings correspond with colors on the Air Quality Index that are meant to help people understand how to protect themselves and what activities they should avoid.
“’Is it OK to go outside?’ is what I need to know, and that’s what the AQI gets at,” said Brian Magi, a UNC-Charlotte professor of atmospheric sciences who specializes in air quality and climate.
Elliot Tardif, a meteorologist with the Division of Air Quality, said that while technically the averages used for the Air Quality Index are supposed to span from a midnight-to-midnight period, meteorologists with his team are willing to be more flexible in order to ensure protection during events like this week’s wildfire smoke.
“Mother Nature doesn’t play by midnight-to-midnight time frames,” Tardif said.
What do Air Quality Index ‘codes’ mean?
The Air Quality Index uses colors to indicate the level of risk posed by air quality.
“When you see those colors, you can associate that with how much of an effect that air pollution will have on a population as a whole,” Magi said.
The Air Quality Index in North Carolina is usually Code Green, meaning there are no restrictions for anyone. When pollutants rise into Code Yellow, the U.S. Environmental Protection Agency recommends people who are particularly susceptible to respiratory irritation think about reducing long or intense activity outdoors.
The next level, Code Orange, indicates the situation has begun to escalate and DAQ typically triggers press releases and public warnings. Under Code Orange, children, older adults and people with lung diseases should cut down on outdoor activities.
At Code Red, people in those those groups are supposed to avoid exerting themselves completely. Everyone else should consider cutting down on prolonged or heavy exercise or work outside.
The next level — Code Purple — is considered very unhealthy. When air quality reaches Code Purple, sensitive groups should avoid all outdoor exertion. Depending on the pollutant in question, outdoor workers or those with low incomes should also consider not exerting themselves outside. And everyone else should avoid “prolonged or heavy exertion,” according to the EPA.
Code Maroon is the highest risk level, only appearing when the air is deemed hazardous. When ozone pollution reaches those levels, the EPA recommends that everyone avoid exerting themselves outside. For PM2.5, everyone should avoid outdoor exercise or work while people with heart and lung disease should stay inside and avoid high levels of activity.
What are dangerous levels?
The N.C. DAQ measures fine particulate matter, also known as PM2.5, and ozone that hovers near the ground level. The Environmental Protection Agency tells agencies like DAQ what pollution levels correspond with certain warning levels.
With PM2.5, for example, the EPA calls for a Code Orange when the 24-hour average reaches 35.5 nanograms per cubic meter. That means the air quality is dangerous for children, older people and those with respiratory conditions.
DAQ must issue a Code Red when the 24-hour average is at least 55.5 nanograms per cubic meter. Air is classified as very unhealthy at 150.5 nanograms per cubic meter, and hazardous at 250.5 nanograms per cubic meter.
Ozone reaches Code Orange when it averages .071 parts per million over an eight-hour period. When ozone reaches at least .086 parts per million, Code Red, the EPA recommends that everyone avoid outdoor activity.
Above .3 ppm, the EPA recommends that everyone avoid all outdoor exertion.
The EPA occasionally tweaks how it classifies risk levels, but what those risk levels mean stays consistent.
“The different color codes and what each of those mean never change, but the standards and the breakpoints upon which those are based do change every several years,” Tardif said.
This story was produced with financial support from the Hartfield Foundation and 1Earth Fund, in partnership with Journalism Funding Partners, as part of an independent journalism fellowship program. The N&O maintains full editorial control of the work.
This story was originally published June 7, 2023 at 6:08 PM.