Breathe easy!

“Your home is your castle. Shut the door and you will shut out the world and its problems,” it was once said. But, not anymore. Today, the world — and its polluted air — comes seeping in, through every crack and crevice. Last month, Delhi had the dubious distinction of becoming the city with the worst air quality in the world.

But other Indian cities are not far behind;  many figure in the global Top Twenty of most polluted places: Gwalior, Allahabad, Patna, Raipur, Ludhiana, Kanpur... Southern metros like Hyderabad, Bengaluru and Chennai are only a whisker short of this name-n-shame list, albeit in specific pockets. The villain is  usually fine particle pollution  — called particulate matter (PM). Cities like Pune, Kolkata, Amritsar suffer from  nitrogen dioxide pollution, caused mainly by vehicular emissions. In all these cities,  this is no longer an outdoors-only problem. Air quality even indoors is degrading alarmingly. We are more prone than ever, to respiratory ailments and by ‘we’ one means especially the very young and the old who are more vulnerable.

If you live in an apartment or house that is on a busy road,  or near a smoke emitting industry, chances are you are  more in danger of the effects of air pollution. An air purifier will provide definite relief and may prevent frequent visits to the clinic.

All air purifiers improve the air quality, some better than others. Their basic function is to filter out the particulate matter for which they all use what is known as a HEPA — High Energy Particulate Arrester — filter. This is usually classified as a PM 2.5 filter which means it can remove particles of dust, soot and smoke, larger than 2.5 micrometers in size.

Just to give you an idea, a human hair is 100 micrometers in thickness or 40 dust particles in a row. These ultra fine particles can go straight to the lung and can trigger chronic disease such as asthma, bronchitis and other respiratory problems. Even larger particles up to PM10 or ten micrometers pose a health concern because in spite of the human body’s own filtering mechanisms, they are small enough to be inhaled. Indoor Air Purifiers depending on the make, also come with some other filtering mechanisms: courser  filters to take off visible dust; ultra violet ray generators to kill some germs; special filters to address fungal spores and pollen which many people find allergic; active carbon to absorb bad odours — even a bit of Vitamin C to deodorise the air. Thanks to the air quality crisis in north India this year, a dozen brands of indoor air purifiers are available all over India — Atlanta, Blue Star, Kent, Eureka Forbes, Honeywell, Moonbow,  Nirvana  Panasonic, Philips,  Samsung, Sharp and Xiaomi to name a few.

Typically, such purifiers cost between `15,000 and `40,000 and are good for average sized apartments, covering 25-60 square meters. Each make  has some special claim.

Do indoor air purifiers work? The Energy Research Institute (TERI) carried out a study  earlier this year, using Sharp units in three different types of locations  in Bengaluru and Delhi, over a period of two months. Results showed that irrespective of the building type, the performance of the air purifiers improved with time. The maximum reduction in fine particles as well as harmful gases, was observed when the air purifier runs for 90 minutes. So clearly they do help clean the air.  Unless the environment in Indian cities improves sharply, we may  have to resign ourselves to increasingly cleaning the air we breathe, even as we are used to cleaning the water we drink.  There is a new enemy within. We ignore it at our peril.