Two weeks after a Christmas Eve fire at U.S. Steel's Clairton Coke Works, the Allegheny County Health Department warned residents to limit time outside because of potentially dangerous levels of sulfur dioxide in the air. Three months later, Mon Valley residents say it’s still affecting their quality of life.

“It’s still at times pretty bad, certain mornings, and in the night it’s really bad all the time,” said Jim Ross of Clairton. “My wife has a bad heart and it causes her a lot of breathing problems.”

Esther Spadaro has lived in Clairton most of her life. She said she would like to know more about what is in the air she breathes.

“I know nothing really, but I know that sometimes I can’t breathe as well,” she said. “Some days it’s an awful toxic smell. It’s not every day, but the result is black soot on my porch, in my house … I am concerned.”

Resident say the emissions smell of burning matches or rotten eggs, and can burn the throat and eyes. When sulfur dioxide combines with water – like the water on the surface of your eyes or in your airway – it becomes sulfuric acid, a severe irritant.

“In the same way, sulfur dioxide can interact with water vapor in the atmosphere and also be converted to sulfuric acid,” said Jim Fabisiak, Director of the Center for Healthy Environments and Communities at the University of Pittsburgh Graduate School of Public Health. That sulfuric acid, suspended in the air, is one of many particles that makes up a class of pollutants called particulate matter.

“We know from a variety of health effects studies that particulate matter … is associated with increased risk of cardiovascular events, premature mortality, enhanced respiratory effects, as well exacerbations of chronic obstructive lung disease, even adverse birth outcomes,” he said.

Fabisiak said scientists don’t quite understand the biological mechanisms that lead to these outcomes – and in fact, it’s a matter of debate among the public health community – but there are several theories.

One theory is that the irritation to the lungs caused by particulate matter affects the autonomic nervous system – that is, the part of the nervous system responsible for involuntary bodily processes such as respiration and digestion.

“And then that has effects on your heart rate,” Fabisiak said. “If you have preexisting cardiovascular disease then that change in autonomic tone to your heart could push you a little bit in the direction of having an adverse event, an arrhythmia, something like that.”

Scientists also still don’t know which forms of particulate matter are most responsible for the adverse health outcomes.

In the meantime, the health department continues to closely monitor air quality in the region.

U.S. Steel has said it anticipates having the damaged equipment repaired by April 15.