Due to the wildfires that have devastated Northern California, the air quality in cities like San Francisco, Stockton and Sacramento have exponentially worsened, ranking them among the most polluted cities in the world.

According to PurpleAir, which accumulates air-quality data across the globe, California had worse air pollution levels than cities in India and China on Friday, which frequently rank among the worst. The wildfires are the Woolsey and Hill fires around Los Angeles, and the Camp Fire north of San Francisco. The entire town of Paradise was burned to the ground and the fires raged across 222 square miles of the Sierra Nevada. 

Dan Jaffe, an environmental chemistry professor at the University of Washington, referred to the pollution levels as an "air quality emergency," claiming that the current crisis could undo decades of air-quality progress. "It appears to be the worst air quality ever experienced in San Francisco," he said. 

In San Francisco and the surrounding Bay Area, the smog was so thick that many schools were prompted to close, and the city's cable cars were shut down. However, at UC Berkley, who chose not to cancel classes on Thursday, students chose to write a letter to the administration citing their negligence. "Campus buildings are not equipped to filter out the pollutants making the air indoors just as harmful as it is outside,"a student wrote. 

Many experts have attributed the worsening wildfires to climate change, as exceedingly dry conditions only exacerbate the fires' severity. This means that health conditions will most likely worsen as well, putting increased pressure on the human body. 

Dr. John Balmes, a physician at the University of California at San Francisco, explained, “We’re going to have more situations like Paradise. Hopefully, a good outcome from this tragedy will be that we get serious about this.”