Study finds in-car rush-hour exposure to some particulate pollution twice as high as previously thought
A new study, part of the Atlanta Commuter Exposures (ACE) Study, has assessed on-roadway in-cabin particulate pollution (PM2.5) collected from scripted rush hour commutes on highways and on non-highway side streets. Reported in the journal Atmospheric Environment, the study found that levels of some forms of harmful particulate matter inside car cabins are twice as high as previously believed.
Most traffic pollution sensors are placed on the ground alongside the road and take continuous samples for a 24-hour period. Exhaust composition, however, changes rapidly enough for drivers to experience different conditions inside their vehicles than these roadside sensors. Long-term sampling also misses nuanced variabilities caused by road congestion and environmental conditions.
To explore what drivers are actually exposed to during rush hour, researchers from Duke University, Emory University and the Georgia Institute of Technology strapped specially designed sampling devices into the passenger seats of cars during morning rush hour commutes in downtown Atlanta.
The devices detected up to twice as much particulate matter as the roadside sensors. The team also found that the pollution contained twice the amount of chemicals that cause oxidative stress, which is thought to be involved in the development of many diseases including respiratory and heart disease, cancer, and some types of neurodegenerative diseases.
We found that people are likely getting a double whammy of exposure in terms of health during rush-hour commutes. If these chemicals are as bad for people as many researchers believe, then commuters should seriously be rethinking their driving habits.—Michael Bergin, professor of civil and environmental engineering at Duke
For the experiment, Roby Greenwald, a research assistant professor at Emory at the time, built a sampling device that draws in air at a similar rate to human lungs to provide detectable levels of pollution. The device was then secured to the passenger seats of more than 30 different cars as they completed more than 60 rush hour commutes.
|A schematic of the sampling device built by researchers to measure levels of toxic particulate matter present during rush hour inside of a typical car cabin. Click to enlarge.|
Some drivers took highway routes while others stuck to busy thoroughfares in downtown Atlanta. While other details like speed and having windows rolled down varied, all of the sampling found more risk in air exposure than previous studies conducted with roadside sampling devices.
There are a lot of reasons an in-car air sample would find higher levels of certain kinds of air pollution. The chemical composition of exhaust changes very quickly, even in the space of just a few feet. And morning sun heats the roadways, which causes an updraft that brings more pollution higher into the air.—Heidi Vreeland, first author of the paper
Reactive oxygen species found by this study can cause the body to produce chemicals to deal with the reactive oxygen. Particulate matter causes the same response. In combination, the exposure triggers an overreaction that can be destructive to healthy cells and DNA.
Oxidative stress is thought to play a role in a wide range of diseases including Asperger's syndrome, ADHD, cancer, Parkinson's disease, Alzheimer’s disease, atherosclerosis, heart failure and heart attack, sickle cell disease, autism, infection, chronic fatigue syndrome and depression.
There’s still a lot of debate about what types of pollution are cause for the biggest concern and what makes them so dangerous. But the bottom line is that driving during rush hour is even worse than we thought.—Michael Bergin
The work was supported by the United States Environmental Protection Agency (RD834799).
Heidi Vreeland, Rodney Weber, Michael Bergin, Roby Greenwald, Rachel Golan, Armistead G. Russell, Vishal Verma, Jeremy A. Sarnat (2017) “Oxidative potential of PM during Atlanta rush hour: Measurements of in-vehicle dithiothreitol (DTT) activity,” Atmospheric Environment, Volume 165, Pages 169-178 doi: 10.1016/j.atmosenv.2017.06.044