After days of below-freezing temperatures and snow, Central Maryland is now under a code orange air quality alert through at least late Tuesday, according to a National Weather Service spokesman. Here’s what that means.

What is an orange air quality alert?

An orange air quality alert targets children, the elderly, and those suffering from breathing disorders, who are advised to limit activities outdoors during this time. The air quality alerts are issued on a scale: green (good), yellow (moderate), orange (unhealthy for sensitive groups), red (unhealthy), purple (very unhealthy) and dark purple (hazardous).

Why is an air quality alert being issued?

The air quality alert has been issued because of an inversion, and the wintertime buildup of smoke and emissions in the atmosphere from home heating plants, says the weather service spokesman. According to the Maryland Department of the Environment website, an inversion occurs “when temperature increases with increasing height. Normally temperature decreases with increasing height. … Inversions act as a lid and trap whatever is emitted between them and the ground.”

We hear about air quality alerts during summer all the time. Is it unusual for one to be issued in February?

According to the weather service spokesman, inversions are not uncommon during winter and occur when high-pressure systems coupled with calm winds produce stagnant air.

Who issues air quality alerts here?

The Maryland Department of the Environment.

When will the air quality improve?

Air quality will improve by Wednesday after a front passes through late Tuesday evening, according to the weather service.