Surviving Pollution 

North Indian winters used to be a magical time; when the eternal heat that dominates the subcontinent lifted, and it was pleasant to be outside. These days, temperatures still fall, but you can no longer be outside without a mask. I, Dhruv Mathur Gupta, have been obsessed with mitigating the ill effects of pollution for over a decade now. 

In College, I wrote my senior thesis on the usage of vitamin B6, B9, and B12 to mitigate T-helper cell deterioration. At the Brookings Insitute, working with Dr. Shamika Ravi (Member of the Prime Minister’s Economic Advisory Council), we studied how crop fires impacted childrens development. After leaving the think-tank, I developed an air purifier that was several times more efficient at combating air pollution in Indian homes through a novel method of airflow. My brother and I have asthma, and my grandfather, Padma Sri DP Sinha, recently passed away due to pollution related lung-injuries. 

So when the pollution spikes, wealthy households rush to buy air purifiers. And YouTube reviews promise quick answers. But the purchase is not that simple. There is a layer of calculation behind choosing the right machine for your room and most buyers never see it. This blog is my decades of obsession and research condensed. 

What is Air Pollution and Its Type

According to the WHO, air pollution is the contamination of indoor or outdoor air by any agent that changes the natural state of the atmosphere (1)

 A 2019 study on India shows that air pollution falls into three main types(2):

1- Outdoor Particulate Pollution

It comes from biomass burning, dust, coal use, stubble burning, waste fires, construction work, traffic, and diesel generators. These activities create particles of size 0.1, 2.5, and 10 particles. PM0.1 and PM2.5 are too small for the nostrils to block and can settle deep inside the lungs, increasing the risk of cancer.

2- Household Air Pollution

It is caused by using solid fuels such as wood, dung, crop waste, and charcoal for cooking. From 1990 to 2019, exposure to household air pollution in India dropped by 64.2%.

3- Ground Level Ozone

forms when chemicals like nitric oxide and other volatile gases from vehicles and factories react in sunlight and mix with ozone in the air. Breathing this gas can irritate and harm the lungs.

How to Select Best Air Purifier

Before you jump to YouTube reviews or product ratings, there are a few important things you should do:  

1- Check for Clean Air Delivery Rate or CADR

It tells you how much air the purifier can clean.  

2- Calculate the Volume of Your Room

First calculate the surface area :

1. Surface Area of Room = 10 ft * 6 ft = 60 ft  
2. Volume of Room = 60ft²*7 ft (average height of Indian home) = 420 ft³   
3. Volume in Meters = 420 ft³ / 27 m³/ft³  = 15.55 m³  

3- See How Sealed Your Home is

1. Do you have large gaps beneath your doors  
2. Are there windows that allow wind in?   
3. Do you feel a draft?

The more open your room is to outside air, the more CADR you need. Usually you need between 4 to 10 times your room volume, depending on how much outside air leaks in.

In short :  

1. Minimum CADR (sealed/poor ventilation room) =  3.5 * 15.55 = CADR of 54.2 m³/h  
2. Maximum CADR (well ventilated room) = 10 * 15.55 = 150.55 CADR 

Your goal is simple. Try to get the highest CADR for the money you spend. You do not need the extra features. 

Features To Check Before Buying Air Purifier 

1- Noise

A small purifier that offers a high CADR will make more noise. This happens because noise rises as the fan works harder. Small fans need to spin faster to move enough air. Bigger fans can move the same amount of air with fewer spins, so they stay quieter.

2- Electricity

A purifier should not use more power than a normal ceiling fan. If it does, skip it.

3- Filter Cost

You will likely need to replace the filter once a year. Make sure the replacement cost is reasonable.

4- Size

Most homes already have limited space. Pick a purifier that fits your room without getting in the way.

The next point is not about purifiers but about so-called air purifying plants. These plants do not clean indoor air. They only release a small amount of oxygen. Oxygen is already present in the room, the real problem is the heavy load of particulate matter. And plants like the snake plant produce far too little oxygen to make any real difference. (3)

Advices

1- Keep Airflow and CO2 in Check

Do not let clean air sit in one corner. Keep the ceiling fan on the lowest setting to move the air gently. Poor ventilation can also raise CO2 quickly, so if levels cross 600 ppm, increase circulation by opening a window slightly or improving airflow.

2- Place the Purifier Higher

Putting the purifier higher in the room helps keep it away from the heavier dust that collects on the floor. This keeps the filter cleaner and improves airflow.

3- Pollution Timing

AQI data from Noida on November 12 to 13 shows that pollution peaks at night and is lowest during the day. This pattern repeats often in winter, so night-time purification matters the most.

4- Stay Safe Inside Your Car

Keeping the windows closed and using the fan on recirculation keeps indoor car air fairly clean. Car filters are not true HEPA, but they still recycle the cabin air through a decent filter again and again, keeping the AQI inside stable and low.

DIY Air Purifier

If you plan to build your own purifier, choose the strongest fan you can find. Use a blower, not a regular suction fan. Suction fans need a proper casing to work well, and making that at home is difficult. 

Aim for strong wind pressure and direct the airflow straight onto the filter. This will be loud, but it will clean better. 

Suction fans will stay quiet, but they will not create enough pressure to pull air through the filter. The cleaning will be weak and the filter will not do much. 

If you want real performance, go with a blower and accept the noise. 

Issues with DIY Air Purifiers

1- Unknown CADR

You will get clean air if you put a filter on a fan, but it is difficult to know how much clean air you will get. If your DIY purifier has a CADR of only 5 m3/h, it will be useless in almost every room.

2- CADR Drops Fast

As the filter gets dirty, the cleaning power drops. Since DIY setups usually use weak fans, the drop happens even faster than in normal purifiers.

3- Poor Sealing

If the filter is not sealed tightly, air will leak out from the sides instead of going through the filter. Unless you clamp or epoxy it well, this will happen.

4- Noise

If your DIY purifier is actually effective, it will be loud. You need a strong fan to push air through the filter, and strong fans make noise. 

Conclusion

Pollution in Delhi and the NCR region has reached an all-time high, and air purifiers have shifted from a luxury to a daily necessity for residents. In 2025, the global air purifier market is valued at nearly 18 billion dollars, driven heavily by pollution-hit regions like NCR. This only raises one key question: how do you choose the right purifier? The answer goes far deeper than ratings and YouTube reviews. 

In this blog, I share my thoughts on air purifiers after years of working on them and holding a patent for a dual-sided air purifier. I hope my experience will help you to choose a purifier based on your room size, how well your room is sealed, the filter quality, and proper placement. With this understanding, you can make the right decision, protect your family, and avoid wasting money.