Airparif, which measures city pollution levels, said levels of nitrogen dioxide dropped by up to 40% in parts of the city on Sunday 27 September.
There was almost one-third less nitrogen dioxide pollution on the busy Champs Elyées than on a similar Sunday.
Along the Seine in the city centre, levels were down by about 40%. At the busy Place de l’Opera, levels were 20% lower.
Bruitparif, which measures noise, said sound levels dropped by half in the city centre.
Officials and environmentalists hailed the event as a success despite disappointment that police had refused to allow the ban to cover the whole city. The official intervention meant only 30% of Paris was off limits to vehicles.
City mayor Anne Hidalgo, who has made reducing Paris’s worryingly high pollution levels a top priority, said she hoped to introduce a regular citywide vehicle ban.
“We might envisage days without cars more often … perhaps even once a month,” she wrote on Twitter.
In March, a spike in air contaminants briefly turned Paris into the world’s most polluted city. The noxious smog was so dense it almost obscured the French capital’s totemic landmark, the Eiffel Tower.
In a few weeks, world leaders will fly to Paris for what has been billed as the world’s biggest ever climate change conference.
COP21 will seek an international agreement on dramatic measures to keep global warming below 2C.
In his speech to the United Nations last week, French president François Hollande said it was the “last chance” for climate change and said the international community had an “obligation to succeed”.
French environment minister Ségolène Royal said France has a “particular responsibility to be exemplary to encourage other countries for climate regulations”.
Unfortunately, in terms of pollution, Paris is far from exemplary.
At Quai des Celestins, near Place de la Bastille, on a Friday morning, the traffic speeding along the riverside highway flanking the muggy grey Seine is relentless. A tag-covered white van belches black, noxious smoke. A cyclist following the van puts her hand over her mouth.
In the last two weeks the levels of nitrogen dioxide (NO2) here have peaked at “very high”, according to Airparif. In the last year, the level of NO2 on the quai has regularly topped 100µg/m3 with an average of 66µg/m3 over the year – well above the EU limit of 40µg/m3.
Across town at the Place de l’Opera, the traffic is equally intense, and the figures equally worrying. Here the annual average NO2 level is 95. On the péripherique, the ring road around the city, it has reached 150.
Airparif, an independent monitoring organisation, reports that Quai des Celestins broke the European hourly limit 11 times in 2014. Place de l’Opera broke the limit 17 times, and parts of the péripherique did so 67 times.
The widely published picture of the Eiffel Tower shrouded in smoke this spring symbolised the French capital’s battle with pollution, a battle that has pitted the city authorities against the government – both Socialist and both supposed to be singing from the same songsheet, but frequently at odds over how to solve the problem.
When the scandal broke over Volkswagen’s manipulation of emissions data for diesel vehicles, the French claimed this was typical “German economic arrogance”. Amid the bout of schadenfreude, no one mentioned that France has been flouting EU air quality targets since 2005.
In its report for 2014, Airparif wrote: “Despite meteorological conditions favourable to the quality of air in 2014, 2.3 million French people are still exposed to levels of pollution that do not respect the rules, particularly in the case of (lead) particles and nitrogen dioxide. Those living in the Paris region and near major roads are the most affected.”
Airparif said pollutions levels were up to double those allowed by the regulations. Five pollutants posed problems in the capital: benzene, nitrogen dioxide, ozone and the fine particles PM10 and PM2.5.
A report by the French Sénat, the upper house of parliament, found that air pollution costs France €101.3bn (£75bn) a year in negative health, economic and financial consequences.
It said illnesses created or worsened by pollution included Alzheimer’s disease, heart disease, respiratory disease and some cancers. Polluted air is also linked to foetal development problems, the report said.
Jean-Francois Husson, head of the Sénat committee, said: ”There’s lots of work to do … Europe and states have to act.”
The report – entitled Air Pollution: the Cost of Inaction – estimated that pollution caused up to 45,000 premature deaths in France a year, from asthma, chronic bronchitis, heart attacks, lung cancer and strokes.
The Sénat criticised successive governments for a “failure to mobilise” to clean up the city’s air.
Hidalgo has made doing so a priority. City hall launched an ambitious “anti-pollution plan” at the beginning of this year, which included an eventual prohibition of older diesel vehicles, multi-million euro improvements to public transport and pedestrian area projects – including banning all vehicles from the right bank of the Seine from Bastille to the Eiffel Tower.
However, when pollution spiked in March this year, Hidalgo’s traffic calming measures – including alternate day access to the city for cars – were overruled by Royal at the ministry, leading to a furious public spat between the two women.
Christophe Najdovski, deputy mayor in charge of transport, said Paris was lagging behind on tackling pollution. He said centralised state interference in the city authorities’ attempts to combat pollution were “an obstacle to modernisation”.
“We’re behind on this and we cannot afford to be,” Najdovski said.
“We have to change people’s attitudes and behaviour. The fact is you don’t need a car to get around in Paris and there is no reason to use one most of the time. You can take public transport, bicycles and even walk.”
He said young people were slowly changing attitudes. “The young have a different relationship with cars. They are much less likely to buy a car and more interested in car-sharing and similar schemes.”
Najdovski, a member of the Europe Ecology-Green (EELV) party, admitted he was disappointed that only one third of Paris was handed over to pedestrians and cyclists on 27 September.
However, he said the event was symbolic and aimed to demonstrate that it was possible for people to “move about the city differently”.
Najdovski added: “My dream Paris would be a city without cars. It may be idealistic, but we have to start somewhere. And this is the road we have to go down if we want to have a city we can live in.”