A Code Orange air quality alert, meaning conditions are unhealthy for sensitive groups, is in effect for much of Maryland on Monday, a relatively rare occurrence outside of the summer months.
The alert is because of warming temperatures and a high pressure system that is making the air stagnant over the region, according to the Maryland Department of the Environment. That is causing fine particles to build in the air.
That is different than the common air quality alerts issued during summer months, which are most often linked to high levels of ozone pollution, which can be exacerbated by hot weather.
"In wintertime, it's almost always fine particles," MDE spokesman Jay Apperson said. "That can happen any time of the year."
Code Orange levels were measured both in Western Maryland and the metropolitan Baltimore area Monday morning, according to data from MDE provided to AirNow.gov.