As historic fires burn in California, the CDC has urged residents to set up air purifiers – here’s what to know if you want to buy one

As historic wildfires burn across the Los Angeles area, the Centers for Disease Control and Prevention (CDC) has urged residents to protect themselves from the smoke by staying indoors when possible and setting up portable air filters and purifiers.

For several decades, air quality in the US was trending up by many measures. Data indicated that fine, inhalable airborne particulate matter, known as PM2.5, was declining in 41 states before 2016.