There was a time when winter in the Indian capital was a glorious thing. Clear, sunny days and crisp cold nights.

No longer. Over the last decade air pollution has grown so rapidly that the cold weather turns the city into a grey, smog-filled health nightmare.

New Delhi has earned the dubious distinction of being the world's most polluted major city, surpassing Beijing. While the Chinese capital has made progress in spreading awareness about air pollution and is taking steps to address it, New Delhi has barely begun to acknowledge the problem.

But as hacking coughs linger for months and red, watery eyes itch, a slow awareness is developing.

Some people tie handkerchiefs around their mouths and noses and others wear surgical masks.

Sitesh Singh drives one of the city's many auto rickshaws and suffers from asthma. He has started wearing a surgical mask through the winter and says it helps him breathe.

While surgical masks protect from larger pollution particles they do little to filter out smaller PM2.5, the most lethal particulate pollution that can become lodged deep inside the lungs.

While there is scant reliable data on respiratory illness in India, doctors say the number of cases is rising and the ones they see are more serious.

Over the last week PM2.5 levels have soared above 300 micrograms per cubic meter on some days, 12 times the standard set by the World Health Organization.

When air quality hits hazardous levels in China schools may be closed, industries shut down and government vehicles taken off the roads.

India has no such emergency protocols. Anti-pollution laws remain widely ignored and unenforced. Its fledgling air quality index covers only a few cities with a patchy network of monitors that often don't work.

Globally, air pollution kills millions of people every year, including more than 627,000 in India, according to WHO.

India's air pollution comes mostly from coal-fired power plants, crop burning, domestic cooking with firewood or cow dung, and vehicles burning diesel fuel.