When it comes to measuring the health threat of air pollution, it’s not just about the amount of bad air we breathe. New research finds the chemical composition of what we inhale also plays a big role in assessing the overall threat.

Traditionally, most measures of air pollution have focused on the amount of soot, fumes or other combustion byproducts we breathe. Those are known as particulates. But not all pollution is equally harmful.

Researchers in Switzerland show the oxidative [ox-eh-DATE-iv] potential, or the ability to reduce helpful antioxidants, is what makes particulate pollution so harmful to cells and tissues in the human body.

To establish their findings, they exposed human airway cells to particulate pollution. As the exposure to pollution with elevated oxidative potential increased, so did inflammation in the airway cells. That indicates the pollutant’s oxidative potential ultimately determines how dangerous it is to the body.

What does that mean for humans? For one, it suggests that more dangerous types of pollution may be concentrated in certain areas with particular industrial or commercial activities.

Using computer models covering locations throughout Europe, the researchers found cities with high levels of wood burning or vehicle traffic that produces high amounts of tire wear and brake dust have greater levels of pollution with more dangerous oxidative potential.

The study reinforces previous findings that people living in congested areas have a greater risk for breathing harmful pollution, while adding fuel to the debate that more regulation of the type of pollution is needed.