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Reducing Air Pollution *Inside* Your Car by 80%

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It may be a no-brainer to avoid standing on the sides of highways during rush-hour or in areas of traffic pollution where the air is thick with smog.  Less obvious is how much air pollution and particulate matter we are exposed to inside our cars while driving.

               You may want to consider how much time you spend driving with your windows open.  A study in this month’s edition of Science of the Total Environment gives us pause when it comes to rolling down the windows on our morning and afternoon commutes.  Choosing to put your car’s fan on or setting it to recirculate, rather than rolling your windows down, reduces the amount of troublesome particulate matter by 80%.

               Comparing the particulate matter in cars of ten different cosmopolitan cities across the world (from Ethiopia to Colombia, Bangladesh, China, and India to name a few), researchers uncovered some startling figures about how much pollution we are receiving while driving.  The study also points out some ways to manage or reduce the pollution so we can continue to enjoy fresh air in our cars.

Why Particulate Matter Matters

               The researchers focused on the PM10 and PM2.5 levels.  PM stands for “particulate matter” and describes the measurement of these particles of dust, gas, and other pollutants and irritants.  PM10 is particulate matter measuring 10 micrometers, while PM 2.5 is 2.5 micrometers or less in diameter.  These particles are so small—smaller than a human hair, which measures 100 micrometers—and approximately 40 particles of this size could be lined up on the width of one human hair.

What does this mean for us? These tiny particles are classified as environmental stressors. Breathing in these tiny microparticles means that they infiltrate our respiratory systems where they irritate and inflame our lungs and increase risk of respiratory infections and other health hazards like heart disease.  Tiny particles that accumulate on our skin increases oxidative stress on the body and the skin.  Particulate matter exposure has also been linked to decreases in brain matter size and declining cognition.

The Results Are In

When the levels of PM were compared across the ten cities, all of them ranked the most PM exposure during windows down, with the exposure decreasing by fan-on, and the least exposure produced by recirculation of air through the car.  In Blantyre (an industrial city in the African country of Malawi, bordered by Zambia, Tanzania, and Mozambique), driving with windows down increased the particulate matter by 589%!  Similarly, high figures were found in São Paulo, Brazil (an increase of 1020%).  Driving with the fan on reduced the exposure in São Paulo to 390%—still an extraordinarily high figure.

Across all the cities studied, recirculation of air during driving reduced PM2.5 exposure by an average of 80% compared to windows open. Clearly, choosing to press the recirculate air button our car dashboard will reduce our exposure; but if you believe that you’re not being exposed to that level of pollution, here’s food for thought.  Sitting in a still car at a traffic intersection exposes commuters to 25% of all the exposure that you could have from commuting even though you spend just 2% of your time at these intersections.

We can’t avoid driving—so what solutions do we have?

               In the study, researchers noted that PM exposure was its highest level during the morning hours.  Traveling during the day and night after the peak morning rush hours was correlated with a 73% reduction in PM exposure.

               More coarse particles were in the air while driving with windows down, while finer particles were dominant in the air quality when the fan was on in the car or set to recirculate.  This is reassuring that most car air system filters are doing a good job of removing the coarse particles from the air that is present during fan-on or recirculation.

               While we can’t simply avoid air pollution altogether, we can make simple choices to be more aware of how much time we are spending with our windows down.  Instead of driving with our windows down all the time, we can reduce our exposure by choosing to roll them up for part of our commute, or to roll them up when we are going to be sitting at intersections.  Or, we can change the times of day that we drive with windows down, and keep the windows up during the peak morning hours when pollution is highest.

               Personally, rolling down my windows on the way home after work has always been a huge stress-reliever.  Now it’s a choice we can all feel even better about, knowing pollution is generally lower at that time of day—helping us all to get a breath of fresh air.


Kumar, Prashant, et al. “In-Car Particulate Matter Exposure across Ten Global Cities.” Science of the Total Environment, 1 Aug. 2020, doi:https://www.sciencedirect.com/science/article/pii/S004896972034924X?via%3Dihub.


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