According to the Huffington Post, a fire department spokeswoman in the catalonia region said the cloud was caused when chemicals that were being delivered to a warehouse in the city of Igualada mixed, setting off an explosion.

The Catalan commissioner for interior affairs told El Pais that the cloud is taking longer to disperse than expected because there's not enough wind in the area.

In addition to staying inside, and keeping windows shut, El Pais is reporting that parents are to not pick up their children from school.