Parts of France are experiencing high levels of air pollution, blamed on wood burning, traffic, and dust from the Sahara Desert that has been blown across to the country on a storm.
The Ile-de-France region - which contains the capital Paris - has implemented differentiated traffic, and reduced maximum speeds on roads to reduce pollution.
The prefecture of police in Paris announced the measures on Tuesday, stating they will last until the end of the “episode”.
The fine particle pollution is linked "to wood heating, road traffic and an import of Saharan sand", it said in a statement.
"Meteorological conditions do not allow for efficient dispersion of pollutants.”
Airparif, which monitors air quality in Ile-de-France, forecasts a PM10 particle concentration level of between 50 and 65 μg/m3 - which exceeds the recommended threshold of 50 μg/m3.
The Prefecture also recommended "limiting car travel as far as possible", favouring teleworking and, "if necessary", carpooling.
Other restrictive measures have been taken, including a ban on individual wood heating.
Parts of the north of France also announced measures amid an air pollution alert.
Those affected include the Pas-de-Calais, Oise and Somme regions, where speed limits on roads were implemented.
From Tuesday at 6pm and for the whole day on Wednesday, speed limits are lowered in these departments by 20km/h on all roads where motorists can usually travel at 90km/h or more.
On roads where the speed limit is normally 80km/h, it is lowered to 70km/h.
In the agricultural sector, the prefect recommended postponing the spreading of fertilisers "if possible".