Paris on Monday resorted to drastic measures to curb sky-high pollution by banning all cars with even number plates for the first time in nearly two decades.

In a move that infuriated motorist organizations, around 700 police officers were deployed to man 60 checkpoints around the French capital to ensure only cars with plates ending in odd numbers were out on the streets.

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Public transport has been free since Friday to persuade Parisians to leave their cars at home, and at rush hour Monday morning, authorities noted there were half the usual number of traffic jams as drivers grudgingly conformed to the ruling.

Some, though, appeared unaware of the restrictions that came into force across Paris and 22 surrounding areas from 5:30 am (0430 GMT) -- or chose to ignore them.

"You don't have the right to drive with your number plate," a man on a scooter remarked to another while stopped at a red light.

"Oh really? I didn't know," the second driver replied before speeding off.

The restrictions will be reviewed on a daily basis, with odd numbers potentially banned on Tuesday if deemed necessary -- a decision due to be made late morning Monday.

The government decided to implement the ban on Saturday after pollution particulates in the air exceeded safe levels for five straight days in Paris and neighboring areas, enveloping the Eiffel Tower in a murky haze.

And while these fell to safer levels on Sunday, they inched up again on Monday, though the pollution was not perceptible to the naked eye.

Ban Is 'Hasty, Ineffective'

Parking in the capital was free for vehicles with even number plates Monday, the Paris city hall said, calling on residents to consult carpooling or car-sharing sites to work out their travel plans.

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Those who choose to defy the ban risk a fine of 22 euros ($30) if paid immediately, or 35 euros if paid within three days. Electric and hybrid cars, as well as any vehicle carrying three people or more, are exempted from the ban -- the first since 1997.

The issue has become something of a political football, with less than a week to go before key municipal elections.

The opposition UMP candidate for Paris mayor, Nathalie Kosciusko-Morizet, called the measure a "fig leaf." Ecology Minister Philippe Martin said he understood the "difficulties, the irritation and even anger" over the move, adding: "But we just had to take this decision."

This combination of photos shows the Eiffel tower (R) in central Paris through a haze of pollution.BERTRAND GUAY,KENZO TRIBOUILLARD/AFP/Getty Images

Martin said similar measures in 1997 "had yielded results."

The measure is also expensive, with free public transport costing the RATP -- the state-owned Paris train, subway, tram and bus operator -- 2.5 million euros a day, according to RATP head Pierre Mongin.

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France's Automobile Club Association (ACA), which counts some 760,000 members, denounced the move as "hasty, ineffective" and "bound to lead to chaos".

"This measure had no effect in any country where it was introduced," said ACA head Didier Bollecker. "Drivers are being targeted even though heating is more polluting, but no one is asking for heating to be used on alternate days."

Similar measures have been introduced in a number of cities around the world, such as Athens or Beijing.

In the Chinese capital, the government implemented the odd-even number plate system during the 2008 Olympics, and the result was so successful that authorities set up a permanent, watered-down version of the rules that sees cars banned from the roads one day a week.

But that has done little to alleviate the dangerous levels of particulates in the air in Beijing -- one of the most polluted cities in the world.

In Paris, authorities measure the concentration of particulates with a diameter of less than 10 microns -- so-called PM10 -- in the air to determine pollution levels.

PM10 are created by vehicles, heating and heavy industry, and include the most dangerous particles that measure less than 2.5 microns in diameter, which can penetrate deep into the lungs and the blood system and are cancer-causing.

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The safe limit for PM10 is set at 80 micrograms per cubic meter.

Last week, the concentration of PM10 particulates in the French capital's atmosphere hit a high of 180 micrograms per cubic meter. The smoggy conditions have been caused by a combination of cold nights and warm days, which have prevented pollution from dispersing.