Braking: The Under-Recognized Cause of Air Pollution


When you think of things that cause air pollution, you might think of your car’s tailpipe emissions; however, you might assume that because you pass your yearly emissions test, that your car isn’t emitting any harmful chemicals. But did you know when it comes to urban centers, tailpipe emissions are not the only thing that contributes to bad air quality? Braking, more than tailpipe emissions, is a major cause of air pollution in cities. This information is not often talked about or shared.

More recently though, people are becoming aware of the on-going issue. A study published in the Environmental Science and Technology Journal in January of this year tested the emissions given off by braking. For the study, they created and placed an exposure box around a car’s braking system and gauged the amount of emissions given off and how those emissions affect human lung cells.

They found that the brake wear of cars contributes up to 20% of the total traffic emissions of a standard car and that the fine particle emissions from traffic correlate with increased morbidity and mortality rates. They also found that the metals given off from brake wear damage pieces of the lungs as well as increases pro-inflammatory responses, leading to stress on breathing and on the body.

How does this happen? As explained by environmental scientist Theodoros Grigorats and nuclear engineer Giorgi Martini in their paper ” Brake wear particle emissions: a review”:

The frictional contact between the disc and the pad generates particles of various sizes. During a braking event, the calliper acts mechanically on the pad, which slides against the disc and transforms vehicle kinetic energy into thermal energy. Apart from the mechanical abrasion, vehicle brakes become subject to large frictional heat generation with subsequent wear of linings and rotors. This generates mostly micron-sized particles. Finally, some disc-brake systems require the pads to be in low-pressure contact with the rotor in order to ensure robust brake performance. This leads in higher particle release in the environment.

The Environmental Science and Technology Journal study also noted that while tailpipe emissions may continue to fall with a rise in zero-emissions and low emissions vehicles that the emissions from braking and tires is unlikely to change anytime soon as many are not paying attention to the continuous hazards they can pose.

Although drivers may not be aware of the hazards of brake wear, the National Center for Biotechnology Information reports “an increasing number of researchers and experts have already raised a discussion on the need for regulating emissions from non-exhaust sources including brake wear.”

In order to address the emissions of braking, we would have to live in a society where braking is minimized, which means a significant decrease in stop and go traffic, which is a society that we are a long way away from.

With the increased traffic across Middle Tennessee, especially on busy corridors like I-24, stop and go traffic is a daily nuisance.

So, what can you do? One thing you can do to help protect air quality is to carpool. By carpooling, you are removing a car from the road, reducing traffic (and emissions) and you might even inspire others to carpool as well.

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