Public transport was free for the second day running in the French capital and 22 surrounding towns on Saturday and cars with even number plates were banned from using the roads.
But officials said that, with many families doing their Christmas shopping or leaving for holidays, police would be lenient, concentrating on cars entering the city rather than those leaving.
Other anti-pollution measures include lowering the speed limit by 20km per hour and a ban on the use of wood-burning stoves.
Pollution by fine particles and nitrous oxide hit a 10-year high in Paris earlier this month, leading to the longest use of the traffic restrictions, although they were lifted last weekend and only reimposed on Friday.
Pollution hits Grenoble, Lyon, Alps
Air pollution, the facts:
- Air pollution is the third cause of death in France, after smoking and alcohol.
- Fine particles can cause cancer and set off asthma, allergies, breathing and heart problems.
- Nitrous oxide, which is present in the fumes of diesel engines, can set off asthma attacks and problems for children's lungs.
- The current spell is caused by people using more heating because of the cold, vehicle exhaust fumes, a lack of wind and the trapping of pollutants near the ground because air close to the ground is, unusually, cooler than that higher up.
Grenoble, on the edge of the French Alps, imposed traffic restrictions and made public transport free for the eighth day running on Saturday, banning the most polluting vehicles - about 26 percent of those registered in the area.
The city was the first in France to introduce mandatory stickers showing how much a car pollutes, a measure Paris is to introduce in January and the government hopes will become national.
The pollution peak has also hit nearby Chambéry and Annecy, Lyon and the Rhône valley with the lack of wind and changes in the difference between ground and air temperature creating a "lid" over valleys.
Restrictions on burning vegetable matter have been imposed in the region, 60 percent of fine-particle pollution coming from wood-burning in the Alps.
Snow runs short in ski resorts
With the Christmas holiday rush starting on the roads, traffic monitors advised motorists to leave Paris before 10.00am on Saturday and forecast traffic jams on the A6 motorway heading south.
The cold, dry weather has left ski resorts short of snow, with the last major snowfall on 23-25 November.
But hotel owners report few cancellations, since families heading for the mountains at Christmas and the New Year are less inclined to go skiing than those who visit in February.
Plastic bag fan
In a further anti-pollution measure Paris is to extend its ban on the use of plastic bags made from fossil-based materials to street markets from 1 January.
The city is to hand out three million biosourced bags that can be composted to stallholders to start the scheme off.
Plastic bags take 100-400 years to degrade and their manufacture consumes four percent of the world's petrol and emits greenhouse gases.