On the morning of Thursday, January 13th, MoreThanTheCurve.com reported that the Pennsylvania Department of Environmental Protection had declared a Code Orange for the day.

The declaration was based on a forecast for a “moderately strong temperature inversion Thursday morning with calm or very light wind that will likely contribute to daily average concentrations of fine particulate matter in the Code Orange range.”

Starting the afternoon, social media was filled with mentions of a burning plastic smell. Locally many people looked to the Covanta plant in Conshohocken as the source.

The Philadelphia Inquirer had an article about it today about the smell and there is an explanation from a representative of the Pennsylvania Department of Environmental Protection.

Virginia Nurk, a spokesperson for the DEP, explained that a condition known as an inversion occurred in the Philadelphia area. Residents in the city and across its suburbs noticed and experienced strong odors, mostly described as a burning or chemical smell.

An inversion, she said, “occurs when a layer of warm air is higher than a layer of cooler air, thereby trapping pollutants close to the ground.”

So basically the forecast for the Code Orange came true and the pollution that normally occurs around the area was trapped and not able to spread out into the atmosphere.