FAQ: Do Air Purifiers Work? What to Keep in Mind Before Buying?

Here’s a quick primer on how air purifiers work and what you should be looking for when buying one.

4 min read
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A common misconception when it comes to air quality is that the air inside our home or any confined space is clean and fresh.

However, in reality, polluted air from outdoors seeps and remains trapped indoors – making the air quality indoors worse and perhaps more dangerous if there is not enough ventilation.

If you are living in Delhi-NCR, or any of the other polluted cities of India, buying an air purifier may soon become a necessity rather than a luxury.

Here's a quick primer on how air purifiers work and what you should be looking for when buying one.

How do air purifiers work?

Air purifiers essentially function by sanitising the air – which includes pollutants, allergens and toxins. While a humidifier or oil diffuser adds particles to the air we breathe, an air purifier does the exact opposite of it.

Does this mean it filters the pollutants in the air?

Not really. While air purifier filters pollutants, it can also also 'purify' or 'sanitise' the air you are breathing.

However, whether it can 'filter' or 'sanitise' depends on the type of air purifier you choose. Air purifiers with HEPA filters do a much better job (more on this below).

Are they effective?

Breathing in air that is 100 percent pollutant-free is impossible. So, will the air purifier make sure that you breathe cleaner air?

The short answer is yes.

Again, apart from N95 masks, studies have shown that air purifiers are effective in both filtering and cleansing the PM 2.5 particles.

But how efficient your air purifier is depends on the kind/filter you would be choosing.

What is a HEPA filter? Why does everyone keep talking about it?

Most air purifiers have HEPA – high-efficiency particulate air – filters. This is a thick layer that is said to capture pollutants, both seen and unseen. Air purifiers also have additional filters like a pre-filter to capture larger dust particles, and activated carbon filters for odour and allergens.

The more filter layers there are in the air purifier, the better is its efficiency.

What should you keep in mind while buying an air purifier?

  • Before you purchase an air purifier, decide on where the purifier will be placed. Would you use it just in the bedroom or in the living room.
  • Ensure that your air purifier is the right size for the room you choose. The coverage area of the purifier is mentioned in the description of the product.
For example, say you are purchasing an air purifier to use predominantly in your bedroom. If you choose to also use it in your living room, which is larger in square footage, it may not be as effective as it is in your bed room.
  • The placement of air purifier is also important. Do not push it against the wall as it should be able to take in air from all sides.
  • Not all air purifiers come with digital display of air quality. Check the description if you are particular about digital display.

How much does an air purifier cost?

While you can purchase an air purifier for Rs 5,000, it can also range up to Rs 35,000 or more. It depends upon several features.

If air purifiers work in big spaces, why are activists against smog towers?

There has been wide-ranging debate about installation of smog towers – expected to work like air purifiers – to control pollution levels in Delhi. While air purifiers may work in a closed space, smog towers are ineffective, say activists.

And this has everything to do with the size of space involved.

In 2019, NGO Care for Air’s Karthik Ganesan wrote an open letter and termed smog towers an “ineffective band-aid."

“The air flowing through an indoor space is generally about 100 to 1,000 times greater than what we breathe in the same space. That volume is small enough that one can manage to purify it. The problem is that air flowing through any outdoor space is generally of the order of 1 million to 1 billion times the air we inhale in the same area. This is why indoor air purifiers work well and outdoor purifiers don’t.”
Karthik Ganesan

If I purchase an air purifier, how often should I clean the filter?

Most manufacturers recommend cleaning it once in three months. However, if you are a resident of Delhi and use your air purifier every day during the pollution season, then it is recommended that you clean it once a month.

Should I wear masks indoors if I have an air purifier?

While there is no official guidelines on this, if the pollution levels are extremely high or if the AQI hits the red zone, residents of Delhi-NCR may have to wear mask indoors to protect themselves.

“If you are in a room which has frequent exchange of air from outdoors – say a window or a door – then there will not be much difference with the AQI level indoor. In this case, the air inside your house will be as polluted as outside and it may be advisable to wear masks at all times,” said Dr Arun Sharma, Professor, University College of Medical Sciences, Delhi.

An air purifier will work in tightly closed spaces. If the doors and windows are opened too often, the purifier will not be effective.

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