And you think Beijing is polluted?

The Chinese capital doesn’t make the top 10 list for world’s most polluted cities – and neither does Delhi. But nine cities in Asia do.

Subhra Priyadarshini

doi:10.1038/nindia.2016.165 Published online 21 December 2016

Top 10 polluted cities of the world


China is back in the thick of smog season, so to speak. Beijing was on high alert as a new round of heavy smog descended on the capital and other parts of northern China this month. An air monitor index released by the US embassy in Beijing breached a level that qualifies as what the locals call “crazy bad” air. Top mainland Chinese officials, meanwhile, admitted that China tops the world in almost all types of air pollution.

For people in this region, bombarded with media reports of cancelled flights and smoggy Beijing skies, extreme pollution can often seem a uniquely Chinese problem, the collateral damage of its breakneck development. Yet, China is hardly the only one in Asia bankrolling economic growth with shrinking lifespans.

New Delhi was declared one of the most polluted cities on earth last month after toxic smog engulfed the Indian capital, forcing schools to close and offices to advise workers to work from home. For days, smoke from Diwali crackers refused to leave the flat plains of Delhi as winter set in. More smoke wafted in stealthily from crop wastes that farmers were burning in the neighbouring areas. The city, already gasping for breath with peaking levels of vehicular emissions, construction dust, and garbage and biomass combustion, looked and smelt like it was bombed out.

Ironically, just a few months back in May, an environment official I met in Delhi told me ecstatically, “Neither Delhi nor Beijing.” The World Health Organisation (WHO) had just released its latest global ambient air pollution report and he had come to know that the two smog-tainted Asian cities were not on the list of the worst offenders. His jubilation, however, was ill-placed – the list of the 10 most polluted cities in the world, topped by Zabol in Iran, was still all-Asian, barring Bamenda in Cameroon.

When they were last measured, Indian and Chinese cities accounted for seven of the top 10 cities. The cities on this notorious list harbour huge amounts of microscopic particulate matter, or PM2.5, (measured in micrometres), a 30th of the thickness of human hair and capable of lodging deep in people’s lungs. Four cities from India – Gwalior, Allahabad, Patna and Raipur – and two from China – Xingtai and Baoding – have made the latest list, alongside two from Saudi Arabia (Riyadh and Jubail).

There’s another way of measuring air pollution – by tracking the amount of PM10, or tiny particulate matter 10 micrometres or less in diameter. Both PM2.5 and PM10 are very fine as opposed to coarser particles in pollutants, which can get trapped in the nose, mouth or throat, and so are not as harmful. The WHO currently monitors 3,000 cities in 103 countries around the world, primarily for PM2.5 and PM10.

Asia's top polluted

If drying up of a key wetland and numerous dust storms have pushed the ancient Iranian city of Zabol to the top of the list, it’s Gwalior’s reliance on coal-fired power plants, increasing use of private transport and use of biomass for cooking and heating that has catapulted this historically important city to No 2.

It’s the same story with Allahabad, Patna and Raipur – tier 2 Indian cities with uncontrolled growth in infrastructure and vehicle use. Riyadh and Jubail are choking on sandstorms, pollutants from heavy traffic and industrial waste. In China’s smog-clouded heavy industrial province of Hebei, which houses Xingtai and Baoding, air smells of petrol, thick with pollutants from steel factories, cement plants, factories for building materials, petrochemical industries and power plants.

“A decade ago, you had to explain the word ‘smog’,” says Sunita Narain, environment activist and head of Delhi-based Centre for Science and Environment. “Now you don’t – everyone knows what it is. It’s right there for you to see.”

NASA’s pollution map is one scary picture of the haze over big Asian cities. In their quest for expansion and economic stability, these metropolises have morphed into dust-billowing, haze-covered modern habitats with relentless construction and endless traffic where polluting industries get away with a lot.

Alarm bells rang when the WHO released an estimate of the number of people dying every year due to ambient and household air pollution – the figure today stands at 7 million, give or take a few tens of thousands. A good chunk of these deaths – around 40 per cent – are from China, with its terrible carbon dioxide emissions, according to a study in The Lancet some time back.

During dry winter seasons, South Asia has another demon to slay – the atmospheric brown clouds (ABCs). Mostly affecting people in India and Nepal, particularly living in and around the Indo-Gangetic Plain, this suffocating air pollution brings along soot, sulphates and other harmful aerosols. A 2008 UN Environment Programme study found that ABCs posed grave danger to the water and food security of Asia. The soot conveniently perches on the glaciers, blackening the snow and increasing the absorption of energy. Result: glaciers melt faster in the Hindu Kush-Himalayas, known as the water tower of Asia, endangering the lives of millions of people living downstream.

Bangladesh, not long ago ranked 4th among the world’s most polluted countries, has the added problem of polluting brick kilns that dot most of its urban centres. Cities like Narayanganj, Gazipur and capital Dhaka also continue to reel under hazardous amounts of dust from construction sites and vehicular pollution.

Asian nations have begun to clean up their acts, but it’s an uphill task. Saudi Arabia is trying to convert to using lead-free gasoline and reduce sulphur in fuels by 95 per cent.

When Chen Jining tried to eliminate corruption in China to ensure government officials and companies followed rules, he became China’s most powerful environment minister ever, and a hero of sorts. To foster transparency, his ministry posts all pollution monitoring data on the government website.

Health of the nations

As reports emerged that air pollution is killing about 1.5 million people in India every year, the country decided to become the first among low- and middle-income nations to directly address air pollution as a national health concern. It committed at least US$1.5 billion to addressing household air pollution. The idea is to replace the traditional polluting cooking stoves with clean cooking gas in 50 million poor households in the next 3 years.

“India is in the throes of a silent health crisis due to air pollution that has become the greatest of any major country in the world both in total and per capita [twice that of China],” says Ambuj Sagar, a professor of policy studies at the Indian Institute of Technology Delhi who helped create India’s action plan for lessening the adverse health impacts of indoor and outdoor air pollution.

Delhi, with the highest number of car owners in India, has been pushed to the No 11 position on the dirty list after being on top for two years. When it began feeling the choke last year, its chief minister promised remedies – vacuuming streets, sprinkling water to keep the dust down, greening bald patches of loose earth and the much-debated odd-even rationing of cars based on number plates. Volunteers were put on the streets offering roses to violators to shame them in public. After a brisk but brief war on pollution, the capital lapsed into the usual administrative indifference and lethargy.

That’s bad news for others in Asia. Pollution is hardly the local problem that we imagine it to be. Air doesn’t respect national boundaries, nor do the deadly particles that inhabit it. Singapore and Malaysia’s periodic haze episodes are well known and have become only more severe in the past two decades. Southeast Asia faces the added woe of Indonesia’s smoke haze, a by-product of a US$50 billion palm oil industry.

Research shows haze from India and Nepal is travelling into Tibet, causing pollution spikes on Everest’s northern slopes. In April, scientists at the Chinese Academy of Sciences (CAS) recorded steep pollution levels on the Himalayan slopes. Professor Kang Shichang, director of the State Key Laboratory of Cryosphere Science at the CAS, has monitored the atmosphere of the Qinghai-Tibetan Plateau for more than 15 years. When he saw sudden, unusual peaking of black carbon at an observation site on Mount Everest Station, he listed it as a ‘pollution event’. Scanning satellite images and juggling data, Kang and colleagues figured 97 per cent of the air clusters passing through the station came from north India and Nepal. Air passed most parts of Nepal before climbing over the Himalayas to reach the northern slopes of Mount Everest.

China and India claim to move mountains to make growth less carbon-intensive. Declaring “war on pollution”, China has taken millions of cars off the roads and has shut polluting factories. It promised to reduce emissions from 2030 while making renewables a fifth of overall energy use by 2025. India, home to 22 of the world’s 50 most polluted cities, is trying to enforce the use of high-grade fuel and has removed subsidies for polluting cooking gas. These measures may take decades to show results. After all, the mighty Himalayas aren’t immune.

[Posted with permission from the South China Morning Post, where the article was originally published as an invited commentary on 10 December 2016. Article]