Engineers show how to best
reduce pollution exposure during commutes
By Erika
Ebsworth-Goold Washington University School of Engineering
& Applied Science
For
many, the commute to and from work is a lengthy, stressful process. According
to the U.S. Census Bureau, it takes the average American about 26½
minutes to get to work.
That’s
nearly an hour each day — to work and back — to face traffic snarls and congested
highways.
That commute can also be hazardous to your health, exposing drivers
to an increased amount of air pollutants that have been linked to a whole host
of medical maladies, including cardiovascular disease, respiratory issues and
even lung cancer.
After
conducting a new research approach using actual commutes, a group of engineers
at Washington University in St. Louis discovered a simple shift in driving
habits can help to reduce those risks while out on the road.
“We know that traffic generates a lot of pollution, and therefore it’s the time when you’re traveling in traffic that you can have a disproportionately high amount of your daily exposure to many harmful pollutants,” said Anna Leavey, a research scientist at the School of Engineering and Applied Science.
“What we
wanted to see was: When and where are our highest exposures occurring, and how
should one be driving to mitigate the risk?”
Leavey
and Nathan Reed, a PhD candidate, worked together with PhD candidate Sameer
Patel and Pratim Biswas, the Lucy and Stanley Lopata
Professor and chair of the SEAS department of Energy, Environmental and
Chemical Engineering.
With
assistance from Biswas’s Aerosol and Air Quality Research Lab, they used
portable instruments and sensors to monitor and simultaneously measure
the pollutant levels of their car’s indoor cabin air and the air directly
outside of the car during their own daily commutes. That gave them rare,
real-world look at pollutant exposure.
“As
aerosol scientists, we had access to state-of-the-art air monitoring
equipment,” Reed said. “Once we began measuring inside and outside of the car,
and started getting numbers back, we were able to confirm our hypothesis
that by controlling our car’s ventilation we could mitigate some pollutant
risk.”
Using
their simultaneous measurement approach, Leavey and Reed were able to test a
number of variables while driving to and from Washington University over a
four-month period starting in 2014.
Using
a dashcam, they were able to identify a given pollutant concentration each time
they were: stuck behind a bus or truck, amid traffic on a freeway, stopped at a
red light, or driving past restaurants or construction work.
They
also used different ventilation settings inside their cars: driving with the
windows open, windows closed, with fan on, and with the air conditioning on.
After
crunching all the data, pollutant measurements, and corresponding weather
conditions, the researchers zeroed in on the best approach to cutting your risk
of pollutant exposure while out on the commute.
Using
the AC reduced the pollutants in the vehicle by 20-34 percent, depending on the
different metrics examined, as well as outdoor concentrations, weather and road
conditions.
“We
found a significant difference between running the fan versus running the AC.
The AC is pulling outside air, running through the same filter with the same
ventilation path as the fan. But there’s one difference: when the AC is
operating: You have a cold evaporator that is cooling the air as it passes,”
Reed said. “This cold surface attracts the pollutant particles, and they
deposit there, as opposed to diffusing it into the air you’re breathing.”
That
particle deposition offered varying degrees of pollution protection, but was
most boosted at points of elevated exposure during the commute, such as
following a bus or large truck.
When
windows were closed, and following a bus, the particle concentration in the
outdoor air was 3 times higher than the indoor air. What’s more, no in-cabin
carbon dioxide concentrations were measured during 75 percent of the journeys
made with the AC on.
Biswas
says the new research, recently published in the journal Atmospheric
Environment, “proves that studies such as this can offer insights and provide
mechanistic insights. While some results are obvious, certain other
findings are not, but more importantly accurate scientific data is essential to
back up our results and conclusions. It also indicates that newer cabin
filtration or air cleaning techniques are much the need of the day, especially
for urban commuters.”
Keeping
the windows closed also offered a protective boost, anywhere form 8-44 percent
after all factors were taken into account.
“The
vehicle cabin can be viewed as a buffer, protecting us from the outside air,”
said Leavey. “While driving with your air conditioning on and windows closed is
the most protective thing that you can do, running the AC can decrease your
fuel economy. That’s why adopting a dynamic behavior modification approach is
recommended, in which the AC or closed windows are used when following a highly
polluting vehicle, or on the freeway which tends to be more highly polluted.
Once you have left the polluted environment, we recommend opening your windows
to remove any pollutant build-up from your car.”
This
research was funded by the Lopata Endowment Fund and the McDonnell Academy
Global Energy and Environmental Partnership (MAGEEP) at Washington University
in St. Louis.