On Paris' first "car-free day" on September 27th, when vehicles were prevented from driving in the city center, exhaust emissions were cut by almost 40 percent, according to The Independent. That newspaper noted that the organization Airparif typically measures pollution in the city and found that rate. 

This was a significant drop, considering that cars were banned from only 30 percent of Paris. The Independent's reporting noted that nitrogen dioxide, a greenhouse gas, varied from 20 percent at Place de l'Opera to 40 percent near the center of the city.

Quiet settled in too, as noise pollution was decreased by half, as The Guardian reported.

In 2014, Paris tried a different tactic, banning license plates with even numbers for a day, which decreased air pollution by six percent. But pollution has caused frequent smog haze around the Eiffel Tower, reported by The Independent in March.

So far, Paris's actions have been one-day tryouts, but in comparison, in 2003 London began charging drivers to bring cars downtown. The change there received much criticism, but has reduced both traffic fatalities and air pollution, as Smithsonian reported.

Paris's Socialist mayor Anne Hidalgo tweeted that the city would have other car-free days in 2016.

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