Check this out: see how the Eiffel Tower is barely visible in this photo? That's because of the high levels of smog that have covered Paris and other areas of northern France.
A similar phenomenon happened last year. Then and now, officials took emergency measures including lowering speed limits and banning trash fires to try to prevent even more pollution from building up.
What's causing the smog to build up? There's a high pressure area that's preventing pollutants from escaping and leading to a murky haze as seen in these photos.