With the deteriorating air quality in the metros, more and more people are becoming prone to respiratory diseases.
What can alleviate the problem to an extent is a good air purifier.
But there are certain things one must know before going to buy one.
"If you're going to look for a good, basic air purifier, something that has a HEPA filter is a must," said allergist Jenna Tuck, chair of the American College of Allergy, Asthma and Immunology's (ACAAI) indoor environment committee.
HEPA stands for high-efficiency particulate absorption.
To meet this standard, the filter must remove around 99 percent of particles 0.3 micrometres or larger.
In a recent study, the annual average level of respirable suspended particulate matter (RSPM, or PM10) in residential areas in the Indian capital stood at 209 microgram per cubic metre.
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The levels of PM10 are known to have crossed hit 1,900 micrograms per cubic metre on certain days in some areas in New Delhi.
According to Tuck, although some allergens and particles that cause respiratory problems are smaller than 0.3 micrometers, HEPA filters can remove particulate matter enough to ease symptoms for many people.
People whose noses are particularly sensitive to smell can benefit, too, but HEPA filters can't entirely eliminate odours.
Tuck recommends that people with breathing troubles, allergies or asthma talk to their allergists for advice on whether an air purifier could help them.