A fairly direct way to eliminate air pollution from car exhaust emissions is to simply get rid of the cars themselves.
Next month, Paris officials will attempt to do just that.
Beginning July 1, all cars registered before 1997 will be banned from the city center on weekdays.
The ban also applies to motorcycles registered before 2000.
Cars will display colored stickers on their windshields corresponding to one of six categories for exhaust emissions.
Paris, by Flickr user Alexandre Dulaunoy (Used under CC License)
Initially there will be no apparent penalty for violators, but a fine of 35 euros ($39) will be instituted beginning in October, rising to 68 euros ($75) in early 2017.
Critics of the ban were reported as saying it will disproportionately affect lower-income drivers, who may not be able to afford newer cars.
It's also possible that classic cars may be excused to some extent from the ban, thanks to an exemption for "historic" vehicles (those more than 30 years old) proposed last year.
Paris has declared temporary car bans before, in response to particularly bad smog conditions.
The last ban, in March 2014, removed half of internal-combustion cars from the city's streets for one day, and other half on a second day.
Bolloré BlueCar electric car used for Autolib' car-sharing service in Paris, September 2012
The Paris government also declared a "day without cars" last September.
All non-electric cars were banned from the city center for seven hours that day.
In addition to the standing ban on older cars, Mayor Anne Hidalgo hopes to continue with car-free days, eventually expanding them to larger areas of the city.
Hyundai ix35 (Tucson) Fuel Cell Paris taxi
Diesels have been very popular in France and other European countries for a long time because of their high fuel economy.
But severe air pollution caused by diesel exhaust emissions has created a backlash, leading to calls for restrictions on diesel vehicles, particularly older models that were built to much less stringent emissions standards.