AirParif, the organization which monitors air quality in Paris and the surrounding Ile-de-France region, shared the warning on Wednesday from its Twitter page.
— Airparif (@Airparif) August 24, 2016
Once the level of ozone particles in the air reaches a certain level, authorities have a duty to warn the public.
In order to tackle the level of pollution, residential parking will be free for the entire day in Paris, the mayor's office has announced, and additional measures have not been ruled out.
It is also possible that the Autolib and Velib services would be made temporarily free of charge, “depending on developments in the coming days”, the mayor's office said. It also called on residents of the French capital to use public transport, to car share, or to use environmentally friendly cars if possible.
Ozone pollution is predominantly caused by emissions from cars, and can be dangerous in high levels.
Mayor Anne Hidalgo has put several measures in place to reduce pollution from cars, which has been one of her priorities since taking office. In 2014 she unveiled an ambitious plan to make Paris free of diesel cars within five years, and to “semi-pedestrianize” the city centre.
Other measures to tackle smog have seen monthly car-free days introduced on the Champs Elysees, and the number of cars in the city centre halved on days with a high level of pollution, by introducing alternate-day bans depending on whether licence plates were odd or even.
The World Health Organization says fine-particle air pollution is responsible for about 42,000 premature deaths in France each year.