The City of Light will turn into the City of Smog again on Thursday, at least according to Airparif, which monitors pollution in the capital.
The forecast comes after Paris suffered worrying air quality throughout much of December, seeing public transport made free and traffic restrictions on several days.
Airparif noted in a statement that the pollution level would be "elevated" throughout the day.
This month's surge in Paris pollution has been the most serious in Paris in at least a decade, the group said.
It is estimated that fine-particle pollution causes 48,000 premature deaths a year in France.