How air purifier towers work?

This article discusses the operation mechanism of air purifier towers. We further discuss their efficacy against different polluting species present in the ambient air.

What is an air purifier tower and how does it work

Air purifier towers, also known as smog towers, are large scale air purifying devices. The prototype of an air purifying tower was first built in 2017 by the Dutch artist Daan Roosegaarde, in Beijing.

Working mechanism

An air purifying tower contains many series of fans, which help to pull in air from all directions. Once this air is pulled in, it descends down to the ground surface. 

In this process, it is made to pass through multiple layers of a HEPA (High Efficiency Particulate Air) filter. These filters pick out particulate matter equal to or more than 0.3 microns in aerodynamic diameter.

The main objective of these towers are to carry out large scale air purification, particularly against particulate matter, or simple PM.

Why were they constructed?

Initially, the first air purifier tower was constructed in the Xian district of China. In this district, there has been large-scale pollution, with the air quality reaching hazardous conditions.

The main aim of the air purifier tower was to help to keep in check the levels of PM pollution in the area, in order to improve visibility as well as the air quality.

Two more air purifier towers are present in New Delhi, India. According to the World Health Organization (WHO), India has six of the world’s top ten most polluted cities, with New Delhi, the national capital, standing at the top of the list.

Furthermore, according to a Greenpeace research released in the year 2019, air pollution kills 1.2 million people in India every year.

This was mainly observed in conditions where air pollution is so severe that the ambient air is hazardous to inhale and conditions of smog prevail.

Particulate matter (PM)


Amongst the above mentioned pollutants, the worst is particulate matter, or simply PM. PM refers to particles in the sub-micron range that are suspended in the air. 

There are two forms of particulate matter: coarse particulate matter (PM10) and tiny particulate matter (PM2.5). PM2.5 is a prevalent problem among them.

There are many sources of PM in the ambient air. Some of the main sources include factories, power plants, refuse incinerators, fumes from automobiles, construction activities, fires and natural windblown dust.

Indoor sources include burning of  fuels, smoking, and other hobbies, such as woodworking, painting, etc.

Given the variety of PM present, they have various sources. These particles can originate from a variety of sources, which can be indoors, or outdoor pollution that enters through doors, windows, seeps, cracks, and so on.

PM2.5 is of major concern. It’s small size allows it to reach the deep recesses of the lung alveoli, where oxygen is exchanged with carbon dioxide in the bloodstream.

Several studies on PM2.5 have linked it to several pulmonary diseases, with positive associations found between long term exposure to PM2.5 and lung cancer, and premature deaths in people suffering from preexisting cardiovascular and pulmonary illnesses.

Certain studies have also shown that PM2.5 generated from traffic related air pollution (TRAP) have shown to cause asthma in nonsmokers, children, and adult women.

Smog

Smog, or in this case, photochemical smog, is formed when the gaseous pollutants present in vehicular exhaust react with each other, in the presence of light.

Smog causes multiple health problems, such as difficulty in breathing, eye irritation, asthma, reduced immunity to lung infections, and colds that can be fatal in children. 

The ozone in the smog also inhibits the growth of plants. It can cause widespread damage to crops and forests, and the haze reduces visibility. 

When inhaled, smog irritates our airways, increasing our risk of serious heart and lung diseases. These health risks are why many cities monitor smog levels.

The following pollutants are the dominant gaseous species in a photochemical smog:

Ozone

Ozone is a gas that is formed by interaction of light with oxygen molecules. It is a vital gas in the upper atmosphere, where it blocks the harmful UV rays from entering the atmosphere.

However, when present at the ground level, it has negative implications on human health. 

The characteristic pungent odor of ozone can irritate the inner linings of the airways and can trigger an asthma attack. However, ozone is an unstable molecule, and it can attack the DNA, causing impairment of cellular function.

Various studies have shown that ozone can have adverse effects that include functional,morphologic, immunologic, and biochemical alterations. 

Nitrogen oxides (NOx)

Nitrous oxides, or simply NOx species, refers to the family of compounds that are composed of nitrogen and oxygen in varying numbers. Amongst these, nitrogen dioxide (NO2), is the main concern.

Nitrogen dioxide is a gaseous substance which originates primarily from anthropogenic activities such as vehicular exhausts, emission from industrial chimneys, and combustion of firewood.

Higher concentrations of NO2 are usually associated  with  more  frequent  asthma  symptoms  and  asthma-related problems.

Long-term NO2 exposure lowered lung function measures, according to a longitudinal cohort research published in 2015.

Previous studies have shown a link between exposure to local traffic-related pollution to onset of asthma in children. A study estimated that an increase in NO2 concentration by 20.4 ppb (parts per billion) was associated with a 67% increase in the risk of asthma-related school absence.

NO2 exposures are also positively associated with lung cancer risk in other studies, and also have the highest correlations with all-cause mortality and lung cancer.

Volatile Organic Compounds (VOCs)

VOCs refer to a variety of organic compounds that are emitted from certain materials in the form of a gas. These compounds are present in items commonly stored in houses, such as paints, solvents, cleaning products, cosmetics, and fuels. 

Other sources of VOCs include vehicle refinishing products in repairing car paint, environmental tobacco smoke, stored fuels, exhaust from cars (e.g., benzene) and from emissions from industrial facilities.

VOCs cause irritation in the eye and can also cause respiratory issues, such as difficulty in breathing, asthma attacks, and so on.

However, certain species of VOCs are carcinogenic (i.e., cancer-causing) in nature. Regular exposure to elevated levels of these VOCs, such as in the case of commuters in polluted areas, increases the risk of getting cancer.

How much does it help?

Smog towers usually have a variable capacity, since it primarily depends on factors such as height of the tower, number of filters used, and the pollution levels.

The smog tower built by a Delhi-based company ‘Kurin Systems’ in New Delhi, India, has a capacity to generate 1,300,000 cubic metres of clean air per hour.

To keep the flow of clean air moving, this massive purifier uses forty eight fans. According to the manufacturer, the air purifying tower has the potential to give clean air to 75,000 people living within a three kilometer radius.

In the case of the smog tower present in Xian province in China, which also happens to be the “World’s biggest air purifying tower” standing at a height of 500 metres, it has shown to reduce PM2.5 levels by almost 20%.

However, some research suggests that although it may seem helpful, it is not feasible in the long run. Experts and national media have criticised the air purifier tower  as an “eyewash” and “ineffective.” 

It has been tested by experts at the Chinese Academy of Sciences’ Institute of Earth Environment, who say that amid extreme pollution, the average reduction in PM2.5 has been 15 percent. 

In terms of amount from a given radius, this percentage amounts to a teaspoon from a radius of less than 100 metres.

Furthermore, these towers require a considerable amount of space in order to be constructed, as well as require a high amount of investment.

For example, the air purifier tower present in New Delhi required an investment of Rs. 10-12 crores (i.e., approximately $1.5 million).

All in all, air purifier towers are a solution in the short run. However, in the long run, there is a need of better alternatives, such as less reliance on fossil fuels, cleaner sources of energy, incentivising the use of public transportation or carpooling, and so on.

Other FAQs about Air Purifiers and Filters that you may be interested in.

Air Purifier vs Dehumidifier for Basement

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Can air purifiers help with allergies?

Conclusion

This article discussed the working of air purifier towers, and how they are effective against particulate matter (PM). Furthermore, these towers were also aimed at tackling the gaseous pollutants which are responsible for creating photochemical smog.

However, experts and scientists believe that these air purifier towers are not a reliable solution against the progressive degradation of air quality in urban areas.

This is because their typical efficiency is significantly low, and the area, resources, and capital investment required for one tower is quite high. Therefore, air purifier towers are not worth it.

FAQs

How can I keep myself safe from air pollution?

Avoid places with traffic congestion

As it is evident, traffic-related pollution is a major contributor to many health issues. So, it is best practice to avoid areas which have high traffic congestion or are prone to it. If it is convenient, one should travel in off-peak hours when there’s no traffic.

On the other hand, one can choose an alternate way of transit via a route which doesn’t have much traffic and is economical as well.

Check pollution levels before leaving

If you live in an urban area, it would be a good idea to check the pollution levels before leaving, so that you can plan your trip accordingly. 

There are many government and non-government organisations that are responsible for tracking the concentration of major air pollutants in the city and provide real-time data for the public.

Clean your indoor air

An average American spends 93% of their total life indoors. 87% of their life is inside buildings, then another 6% of their life is in automobiles.

Over the last several years, a significant amount of scientific reports provide evidence of air pollution inside buildings and homes, referred to as indoor air pollution (IAP), which is more serious than outdoor air pollution, even in industrialised cities and metropolitan areas. 

Thus, a person has a higher health risk from indoor air pollution than from outdoor air pollution. The best way to deal with IAP is by the following methods:

  • Improving ventilation of the house.
  • Using an air dehumidifier to reduce the relative humidity of the home.
  • Avoid smoking or combustion of fuels inside the house, as these processes adversely affect the indoor air quality.
  • You can invest in a HEPA air purifier.
    Air purifiers with HEPA (High-Efficiency Particulate Air) filters are best suited for indoor purposes. The presence of an activated charcoal filter and a UV light further increases the efficiency of the filters.

Can air pollution cause lung infections?

Yes, air pollution can cause infections such as bronchitis, hay fever, asthma, COPD, and so on. For people suffering from asthma or have a family history of asthma, the risk of lung infections can be even higher than the rest of people.

When is it safe to exercise outdoors in an urban area?

It would be safer to exercise outside in early mornings, rather than in the evening. In the mornings, there is none to a low extent of human activities. 

Due to this, pollutants such as PM, CO, SO2, NOx, are at low concentrations. Furthermore, since there hasn’t been enough time for daylight, ozone production wouldn’t be occurring as well.

References

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