Several Chinese cities, including Beijing, have dramatically improved their air quality in recent years, while Indian cities remain some of the world’s worst polluted, according to a new report.

Nearly 90 per cent of the 200 cities beset by the world’s highest levels of deadly micro-pollution are in China and India, researchers said.

Taking population into account, Bangladesh emerged as the country with the worst PM2.5 pollution, followed by Pakistan, Mongolia, Afghanistan and India, according to the 2019 World Air Quality Report, jointly released by IQAir Group and Greenpeace.

Among the world’s megacities of 10 million or more people, the most PM2.5 toxic in 2019 was New Delhi, followed by Lahore, Dhaka, Kolkata, Linyi and Tianjin in China and Jakarta. The IQAir report is based on data from nearly 5,000 cities worldwide.

Of cities with more than 1 million people, the least affected by PM2.5 are Adelaide, Helsinki, Stockholm and San Jose in central California, followed by Perth, Melbourne and Calgary in Canada.

Environmental health threat

Particulate matter of 2.5 microns or less in diameter - roughly 1/30 the width of a human hair - is the most dangerous type of airborne pollution. Microscopic flecks are small enough to enter the bloodstream via the respiratory system, leading to asthma, lung cancer and heart disease.

Most of the 7 million premature deaths attributed by the World Health Organisation (WHO) to air pollution are caused by PM2.5 particles, which originate in sandstorms, agriculture, industry, wildfires and especially the burning of fossil fuels.

“Air pollution is the world’s leading environmental health threat. Nearly 90 per cent of the global population is breathing unsafe air,” said IQAir CEO Frank Hammes.

Climate change has begun to amplify the health risk of PM2.5 pollution, especially through more intense forest fires and sandstorms made worse by spreading desertification, the report found. Global warming and PM2.5 also have the same primary driver: the burning of coal, oil and gas.

While the link with lung cancer was well established, a recent study showed that most excess deaths from air pollution are caused by heart attacks, strokes and other types of cardiovascular disease.

Small and larger particulate matter, nitrogen dioxide (NO2), sulphur dioxide (SO2) and ozone (O3) have likewise been linked to drops in cognitive performance, labour productivity and educational outcomes.

China reduces smog levels

Beijing, once infamous for its toxic haze, has reduced smog levels and dropped down the list of the world’s most polluted cities, according to the report. In contrast, India still dominated the list of the smoggiest urban areas, accounting for 14 of the top 20. Ghaziabad is the worst-ranked city.

China’s average urban PM2.5 concentration dropped 20 per cent in 2018 and 2019, but last year it still had 117 of the 200 most polluted cities in the world.

All but 2 per cent of China’s cities exceeded WHO guidelines for PM2.5 levels, while 53 per cent exceeded less stringent national safety limits.

The UN says PM2.5 density should not top 25 micrograms per cubic metre (25 mcg/m3) of air in any 24-hour period. China has set the bar at 35 mcg/m3.

More than a million premature deaths in China each year are caused by air pollution, according to the WHO. Recent calculations put the toll at up to twice that figure.

Across a large swathe of northern India and north-central China, meeting WHO standards year-round for PM2.5 pollution would increase life expectancy up to six or seven years, according to the Air Quality Life Index, developed by researchers at the Energy Policy Institute of Chicago.

Among the club of 36 rich OECD nations, South Korea was the most polluted for PM2.5, counting 105 of the worst 1,000 cities on the index. In Europe, Poland and Italy count 39 and 31 cities, respectively, in this tranche. Other parts of the world such as Africa and West Asia lacked data.

“What cannot be measured cannot be managed. Africa, a continent of 1.3 billion people, currently has less than 100 monitoring stations that make PM2.5 data available to the public in real time,” said Hammes.

As of 2018, China alone had more than 1,000 such stations in 200 cities.

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