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Transportation changes quickly cleaned up the air – now what?

The views expressed are those of the author and are not necessarily those of Scientific American.


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In March, air pollution in northern France reached dangerous levels and resulted in a strong government response. Public transportation fees were removed and cars were partially banned from the roads. This month, as data are released by Airparif, one can see that this response led to a drop in Paris road traffic of 18% and 6-30% drop in air pollution levels.

The majority (51%) of overall particulate matter pollution in the Paris region comes from transportation. Particulate matter (PM) is a mix of liquid and solid particles that can contain sulfates, nitrates, ammonium, carbon, metals, and an array of allergens. PM is described by the size of the particles, measured in micrometers or microns. For instance, PM10 refers to particulate matter that is less than 10 microns in diameter. In Europe, 50-70% of PM10 is actually PM2.5. That is, very mix of very fine particles less than 2.5 microns in diameter.

Both PM10 and PM2.5 are regulated in much of the world. The World Health Organization (WHO) has set recommended concentration levels to avoid the potential negative health impacts of different pollutants. In the case of particulate matter, these impacts include asthma and other respiratory illnesses, lung cancer and cardiopulmonary mortality. Globally, an estimated 800,000 early deaths occur each year as the result of combustion-related emissions (both particulate matter and tropospheric ozone).

According to Airparif, traffic reductions resulted in a 6% overall decrease in particulate matter (PM10) concentrations in Paris with a 10% reduction along the city’s Périphérique during rush hour. Furthermore, nitrogen oxide emissions were reduced by 10-30%(off-peak versus rushhour). These emissions are the ones that go on to form smog and tropospheric ozone. The latter can cause a suite of illnesses including repiratory distress and aggrevated asthma.

According to The Atlantic‘s Feargus O’Sullivan, these reductions are even more impressive because both time and nature were working against the numbers being higher. In his article, O’Sullivan states that:

This [6% drop] is just a single day of driving restrictions…It took place under weather conditions when (thanks to a combination of very cold air by night and rainless, largely windless sunshine by day) particulates were flurrying around Paris’ lower atmosphere like white flecks around a snow globe, unable to escape. The drop thus happened under conditions when natural dispersion of pollution was especially difficult. Given that conditions had worsened over the preceding week, it’s also likely that the pollution drop from the days immediately before that Monday, March 17, was yet higher than the 6 percent contrast with Monday, March 10. All told, the drop shows the clear benefits to be had from a situation that prioritizes public over private transport.”

As the data roll in, the advisability of making these types of mandates more permanent is being more widely discussed. Or, perhaps declining interest in driving in some countries will lead to a similar end result.

Photo credit: Photo of Eiffel Tower by DavidDennisPhotos via Creative Commons.

Melissa C. Lott About the Author: An engineer and researcher who works at the intersection of energy, environment, technology, and policy. Follow on Twitter @mclott.

The views expressed are those of the author and are not necessarily those of Scientific American.





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  1. 1. Pluvinergy 6:36 pm 05/24/2014

    My feeling is that we could apply such practical solutions if were rational about the issue, which we are not and can not be. People, I am talking about the US public. You may know better if we are representative or not, as the chaos of climate change clashes against economic constraint, (read severe hardship.)
    My conclusion then is that in order to confront the issue we need to have valid options. Which is a roundabout way to ask you to consider Pluvinergy. If Pluvinergy was proven practical, then transportation, and for that matter urban design, could be made rational.
    I am the author, so I am biased.

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