New Delhi is once again the most polluted city on Earth

New Delhi, India’s sprawling capital region home to 18.9 million people, is once again home to the worst air pollution in the world.

With the Hindu festival of lights Diwali in full swing this week, New Delhi residents celebrated with fireworks, lamps, firecrackers, and bottle rockets that sent smoke and ash through the chronically congested metropolis.

India’s Supreme Court tried to get ahead of the commotion with a ban on most types of fireworks, allowing only “green crackers” that produce limited noise and smoke, and only for a narrow time slot. But Delhiites were defiant, setting off all kinds of fireworks for hours.

Several Air Quality Index monitors maxed out on Wednesday with a reading of 999. That’s almost double the upper limit of what’s considered hazardous. Of particular concern is small particles that are less than 2.5 microns in diameter known as PM 2.5.

These particles penetrate deep into the lungs and can lead to a variety of health problems ranging from asthma attacks, high blood pressure, and, over the long-term, cancer.

In New Delhi this week, PM 2.5 was so dense that it was like smoking 20 cigarettes in a day. And all across India, particulate pollution surged dramatically during and after Diwali celebrations:

PM 2.5 pollution surged across India after Diwali on November 7.
Berkeley Earth

But it’s not just the fireworks. New Delhi’s air pollution regularly surges in the colder months. That’s because the region’s geography acts as a basin that traps dirty air over the city. And when the weather cools, the wind slows down, allowing the air to stagnate.

About one-third of the pollution choking New Delhi right now doesn’t actually come from the city itself, but from farming regions on its outskirts. Farmers often burn crop stubble after the rice harvest to clear their fields and restore soil nutrients.

The smoke ends up wafting over New Delhi where it blends with urban pollution sources — cookstoves, heating fires, cars, and construction. As temperatures drop, many of the city’s impoverished people burn fires to keep warm while the more wealthy switch on heaters, increasing energy demand from coal-fired power plants.

Air pollution spikes in India during the winter months.
Air pollution spikes in India during the winter months.
Berkeley Earth

The World Health Organization reported last month that 90 percent of the world’s population breathes polluted air, which kills 7 million people per year. And as countries industrialize — build more factories, drive more cars, burn more fuel — the problem is getting worse.

“The world has turned the corner on tobacco,” Tedros Adhanom Ghebreyesus, the WHO’s director general, told the Guardian. “Now it must do the same for the ‘new tobacco’ — the toxic air that billions breathe every day.”

A child holds a firework during Diwali on November 7, 2018 in New Delhi, India. The city is suffering from some of the worst pollution in the world.
A child holds a firework during Diwali on November 7, 2018, in New Delhi, India. The city is suffering from some of the worst pollution in the world this week.
Amal KS/Hindustan Times/Getty Images

Yet even among countries gasping for breath, India still stands out, with many of most polluted cities in the world. Ultimately, the problem comes down to politics.

For one, city politicians have a hard time convincing farmers not to burn crops, which is often the cheapest way to clear fields. And representatives of farming interests have a hard time getting funding to deploy cleaner land management practices.

But to clean up the air, everyone — urban and rural, poor and wealthy — will have to work together. New Delhi’s transportation department has banned heavy-duty vehicles from entering the city for three days and authorities have seized 7,900 kilograms of illegal fireworks as air pollution is forecast to remain severe for at least two more days.

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