Tom Avril uses sawdust to demonstrate how an air filtering system works.

Let’s say your job requires you to be inside with others this winter in a poorly ventilated space. Maybe a windowless room in an aging school building, where the lack of fresh air raises the risk of spreading COVID-19.

Masks will help. Maybe you also want a portable air-cleaning device to help filter particles that may carry the coronavirus. But those can cost hundreds of dollars.

With the overwhelming number of air purifiers on the market, how do you find the best one? Here are some recommendations from CNET.com.