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There's an air quality warning. What does that mean?

Depending on what's in the air, the EPA ranks air quality in a range of numbers.
Credit: WBIR Weather

KNOXVILLE, Tenn. — If you've seen an air quality warning before, you might have seen a color-coded chart. It's easy to guess that green is good, red is bad, and the maroon at the bottom is the worst.

But what do those colors mean in real life, and at what point does it actually impact your day?

For that, we turn to the Environmental Protection Agency's Air Quality Index or AQI. 

Depending on what's in the air, the EPA ranks air quality in a range of numbers. Those numbers are grouped by color; for instance, when the AQI is 0 to 50, the color is green.  Any pollutants in the air are so few, they pose little or no threat. As the threat level grows moving down the chart, here's what each color tells you about what's going on outside.

Credit: Environmental Protection Agency



Green, 0 to 50: Little to no pollutants. Everything's fine.

Yellow, 51 to 100: Moderate air quality. This is still fine for most people, but there starts to be a health concern for a very small number of people who are especially vulnerable to air pollution. 

Orange, 101 to 150:  Most people in normal health still won't likely be affected, but now there is a heightened threat to people who are sensitive to air quality. 

Red, 151 to 200: This is where everyone starts to be impacted. The air is considered unhealthy. People who are sensitive to air pollution could see especially serious impacts on their health.

Purple, 201 to 300: The EPA considers this a health alert. Everyone is at risk of serious health issues because of pollutants in the air.

Maroon, 301 to 500: This is considered a public health emergency. The air quality is an immediate hazard to everyone in the affected region.

If you think your health is more sensitive, talk to a doctor about what to do in moderate to unhealthy air quality.

How often do these alerts happen?

The Knox County Health Department said these colors are just a prediction and not a guarantee of specific air conditions.

Parts of East Tennessee were under an orange prediction on Sept. 16.

"We predict there will be unfavorable conditions for the sensitive receptor groups," said Brian Rivera the county health department's interim director.

"[That group of people] includes the elderly, the children, and people with lung disease."

Rivera said this was only the second time our area has seen an air quality alert, which he said is a pretty good year for air quality.

KNOX COUNTY, Tenn. - A recent air quality report from The American Lung Association shows Knoxville's air isn't great, but it's getting better. "It's much healthier than it's been in the past," Knox County Air Quality Management Director Lynne Liddingdon said.

Does the weather affect air quality?


The weather does play a role. Here's more on how that can happen.

A Code Orange Air Quality Alert will be in effect through Thursday evening for the Tri-Cities, Knoxville and Chattanooga metro areas, as well as in the Smoky Mountains. Ground-level ozone concentrations will be elevated and may reach unhealthy levels for groups with sensitive respiratory systems. Folks that fall into that "sensitive" category should avoid extended periods of time outdoors or strenuous outdoor activities.

Types of pollutants:

Up until now, we've used "pollutants" as a general term for the things in the air that cause problems for us. But those pollutants can be a number of different things. The EPA focuses on five major ones.

Ground-level ozone: ozone's a good thing when it's up in the atmosphere blocking out harmful rays from the sun. When it's down here where we breathe it, we might have lung issues or see smog outside. It comes from cars, power plants, and other fossil fuel burners. It's also worse in the warmer months.

Carbon Monoxide: it's a colorless, odorless gas, and it's poisonous to people. Like ground-level ozone, it can also come from cars, power plants, and industrial combustion, but in carbon monoxide's case, it can get trapped close to the ground during cold weather.

Sulfur Dioxide: this gas is colorless, but it has a strong smell. It's produced when people burn coal and oil fuel that contains sulfur. Normally, your nose can filter out sulfur dioxide, but heavy breathing through your mouth is a different story. You might start wheezing and having shortness of breath. Sulfur dioxide also contributes to forming particulate matter in the air.

Particulate matter: as the name suggests, this involves tiny particles of solids and liquids that are now airborne, and could possibly get breathed in. This can come from grinding activities and dust on the roads. It can also come from forest fires, power plants, and cars on the road.

Nitrogen Dioxide: this is emitted by cars, trucks, buses, power plants, and non-road engines and equipment. Exposure to nitrogen dioxide has been associated with a variety of health effects, including respiratory symptoms, especially among asthmatic children, and respiratory-related emergency department visits and hospital admissions, particularly for children and older adults.

There are ways to reduce these pollutants like ground-level ozone. Reducing your driving time is one of those ways.

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