Some areas of Northern California that were ravaged by the deadly Camp Fire now have the worst air quality in the world, new readings show.

The US Environmental Protection Agency’s Air Quality Index assigns numbered scores based on how harmful prolonged exposure would be, with levels between 201 and 300 deemed “very unhealthy.”

In the Northern California towns of Oroville and Chico, air-quality levels were around 500 on Friday, according to unofficial readings by the private air-quality-tracking company Purple Air.

That’s the highest score measured by the EPA.

Breathing air at that level for 24 hours is akin to smoking a pack of cigarettes a day, The Mercury News reported, citing a University of California, Berkeley, study.

Beijing, infamous for its toxic air quality, measured 93 on Friday.