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An inheritance of smog

Air pollution causes lung diseases and affects pregnancies. It also takes a deadly toll on infants and children. To tackle it, we must understand what it is

Students in Delhi’s Mayur Vihar locality cover their faces with masks on 22 October
Students in Delhi’s Mayur Vihar locality cover their faces with masks on 22 October (HT file)

Even as the baby coughed in her crib, her parents refused to acknowledge what the doctor said. While there can be various causes for coughs and stuffy noses, the doctor had said the air pollution in Delhi was the likely trigger. He had added that such cases had risen sharply over the years, especially around winter. He had advised them to keep the child at home in an air-purified room.

However, the parents refused to purchase an air purifier despite being able to afford it. They believed that these devices would make her weak; that she would lose her immunity and become more vulnerable when she stepped out if she used a purifier at home.

This is a rather common view, and is one of the most common questions I am asked. The belief among people is that we can become immune to air pollution if we are exposed to some of it. Unfortunately, this is wrong—and, sometimes, dangerous.

To understand why, let’s start by understanding what air pollution is, and how it impacts the human body. Air pollution is an umbrella term for various constituents in the atmosphere that are potentially harmful to humans. These include particulate matter, carbon monoxide, sulphur dioxide, nitrogen dioxides, and so on. Each of these impacts the human body differently.

Key among these pollutants is particulate matter, which is at the heart of the air pollution debate as its levels are frequently several times the safe limit. Particulate matter consists of various components, including organic chemicals, metals, acids and dust particles. Such matter can originate from various anthropogenic sources, such as vehicles, power plants, construction sites, cooking, manufacturing industrial units and agricultural stubble burning, which is a major contributor of particulate matter in most northern states during the October-December period, when the great smog descends.

Such particulate matter (PM) can be of various sizes. The kind that is most harmful to human health is PM 2.5 and smaller, where 2.5 refers to size in microns. These PM 2.5 particles are about one-twentieth of the width of a human hair, and are invisible to the naked eye. There are finer particles still, such as the deadly PM 0.1, which is just 0.1 microns small. Human hair, by comparison, is 50-70 microns in width.

While the human body has natural defences to keep us healthy by restricting the intake of pollutants, these defences fail when confronted by such small particles. When inhaled, such ultra-fine particulate matter flows through our filters and through the lung tissues into the bloodstream, much like the oxygen molecules that the human body needs.

This can lead to critical health impacts. People exposed to high levels of air pollution have been observed to have enhanced frequencies of genetic damage and genotoxic effects. In some cases, this manifests itself in the form of cancer. Lung specialists in Delhi today often point out how the share of non-smokers among lung cancer patients has been rising sharply.

Studies have also proven the link between air pollution and health ailments, including brain ischemia, heart rate variability, heart attacks, strokes, congestive heart disease, thrombosis, lung inflammation, asthma, and even depressive and cognitive disorders. A study by the National Physical Laboratory, Delhi, has also indicated the link between pollution and vitamin D deficiency from the lack of adequate sunlight due to the haze. Another study published in Lancet Planetary Health in July last year even revealed a link between air pollution and diabetes.

Pregnant women are vulnerable as pollution has been known to cause foetal growth problems, low birthweight and increased mortality. Carbon monoxide can enter the body of pregnant women and prevent adequate oxygen reaching from the foetus. A study in Tamil Nadu, published in Environmental Research in 2018, showed that every 10 unit rise in PM 2.5 pollutants led to a 4g decrease in birthweight. In Delhi, PM 2.5 levels remain over 300 units during peak pollution season, implying a significant impact on pregnant women.

Air pollution is one of the top three killers in India, ahead of even smoking, high cholesterol and drug use. Even short-term exposure to it can be deadly. The American Lung Association very plainly states that “short-term exposure to particle pollution can kill. Peaks or spikes in particle pollution can last for hours to days. Deaths can occur on the very day that particle levels are high, or within one to two months afterward". We don’t hear of such instances as they are far too fragmented, playing out silently in hospitals and households, away from the media glare.


While the health impact on adults is grave, children are particularly affected as they draw in more air as a share of the body weight. Apart from anecdotes by paediatricians of how the number of young patients suffering from lung issues has increased, we have evidence from scientific studies that back up the seriousness of the issue.

The Chittaranjan National Cancer Institute (CNCI), Kolkata carried out a study profiling over 11,000 schoolchildren across 36 schools in Delhi between 2002-05. The heath of these children was compared to those who live in states where air quality is better. They found that a staggering 43.5% of Delhi’s schoolchildren had reduced lung function. Girls and children from poorer households were disproportionately impacted.

Other studies have shown that when infants are exposed to air pollution in the first years of their lives, while their brains are still developing, they end up experiencing cognitive impacts. Particulate matter can even negatively impact the mathematical and language skills of toddlers.

India’s air pollution crisis is undoubtedly grave. In the face of such a significant challenge, there are several ongoing attempts to address the crisis by reducing the emission of pollutants across the major sectors, including power generation, transport, industry, construction and agriculture. These attempts will take years to make a serious den in pollutants in our local air.

Meanwhile, it is imperative that we minimize the impact on ourselves and those around us. The option to leave Delhi and other polluted areas in northern India is one that is reserved for the most privileged. But for a vast majority, this is not a reasonable solution by any measure.

For the millions who will continue to live in this part of the country, then, it is vital to minimize exposure to air pollutants. This involves, first of all, limiting time in polluted areas, such as around construction sites, busy traffic intersections, or generally outdoors. Second, ensure your home and workplace are insulated from the outside air, which includes plugging gaps around your doors and windows. Third, use air purifiers if you are able to afford them. They do work in bringing down particulate matter provided the room is not exposed to outside air. Weara mask when outdoors, and ensure that it fits well.


Any amount of exposure to air pollution is harmful to human health, so the goal must be to limit exposure. Even if you are only able to be in an air-purified room for a few hours every day, it is an opportunity that must be grabbed. The human body cannot get used to these pollutants, so there is no question of immunity being impacted due to the presence of air purifiers. If anything, we are more vulnerable outdoors if we are also exposed to polluted air indoors.

A related misconception is that indoor plants are enough to tackle air pollution. Plants are great for the local indoor environment in many ways, but they cannot filter out the vast amounts of pollutants experienced in much of India.

This conversation, alas, is a privileged one in itself. Most Indians still live and work in conditions where there is no easy escape from pollution. From professionals who have to work outdoors to people who don’t have homes that can be insulated from the outside air to those who use polluting biomass at home to cook meals to everyone who cannot afford air purifiers or high-grade masks, hundreds of millions of people remain at risk. As I have argued in my book The Great Smog Of India (2018), air pollution is proving to be one of the gravest inequality issues of our time.

It is therefore imperative to create awareness and provide tools for people to protect themselves.This involves reducing local emissions within and around homes and workplaces. This involves public schools and buildings being retrofitted to minimize exposure to pollutants. This involves the provision of subsidized masks to those who remain most exposed. And much more.

It may take years for action against air pollution to fructify. After all, transitions to clean technologies and processes are expensive and time-consuming. It will involve a radical shift in the way we travel, produce goods and generate electricity. Meanwhile, we must do everything we can to protect ourselves—and the children and infants who are dependent on us—from this air that kills.

Siddharth Singh is an energy and climate policy researcher, and the author of The Great Smog of India (2018).

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