What does an air purifier do and can it help with wildfire smoke?

Technically, air purifiers ‘clean’ the air, rather than purify it, Jill Heins, a senior director at the American Lung Association, says. Photograph: d3sign/Getty Images

With smoke from wildfires in Canada and Minnesota spreading across the US, more than 20 states have issued air quality alerts. Local leaders urged people to stay inside as “unhealthy” air quality levels affected the US midwest and north-east.

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.