The city is suffering its worst and most prolonged winter pollution for at least 10 years, the Airparif agency which measures the levels said on Wednesday.
Authorities have said only drivers with odd-numbered registration plates can drive in the capital region on Wednesday. Drivers of even-numbered cars were given the same opportunity on Tuesday, but could now be fined up to €35 if they are caught behind the wheel. More than 1,700 motorists were fined for violations on Tuesday.
Paris mayor Anne Hidalgo said images of smog blanketing the capital were proof of the need to reduce vehicle use in the city centre.
The air pollution peak is due to the combination of emissions from vehicles and from domestic wood fires as well as near windless conditions which means pollutants have not been dispersed, the Airparif agency said.