New Delhi, Nov. 17 -- Running your air purifier around the clock when the AQI is in the hazardous range (anything above 300 and certainly over 400) can make all the difference to your health and comfort, according to doctors and air quality researchers. In a city like Delhi NCR, it's only sensible to keep it running all day long. But it's not a magic fix and in lethal AQI situations, there are hard limits to what any machine can do.

When outdoor AQI soars above 300 and especially during Delhi-like pollution spikes that can see AQI soar up to 1000, unfiltered indoor air fills up with microscopic PM2.5 and PM10 particles. These can slip easily into the lungs and bloodstream. It's no surprise that even brief exposure to air this toxic bring...