New Delhi, India, one of the top cities for air pollution in the world, is bracing for a thick layer of smog this winter.

A process known as burning "crop stubble" will exacerbate smog in cities like New Delhi and Kanpur, India, Bloomberg reported. Farmers traditionally clear their fields after wheat and other grains have been harvested by burning the remainder of their crops to prepare for the next planting season, even though the process was technically banned from parts of the country in 2015.

The smoke from this process contributes to the road construction dust and industrial emissions that bring smog to India year-round.

Low wind speeds are also worsening smog conditions by not "dispersing" the pollutants in the air, India Today reported.

Though the pollution from burning crop stubble is expected to dissipate by spring, it still points to India's greater air pollution problem, especially in New Delhi. There was not a single day in 2017 when air pollution levels in the city were deemed "healthy" for children or adults by the World Health Organization.

What else do you need to know about the blanket of smog in India right now? USA TODAY breaks it down:

Crop stubble burning caused one-quarter of the air pollution in New Delhi in November 2017, according to the Ministry of Environment, Forest and Climate Change.

India is home to the top ten smoggiest cities by both PM 2.5 and PM 10 measures. PM 2.5 are the small particles of air pollution that pose the greatest threat to human respiratory systems, according to the WHO. PM 10 are the larger particles that still pose health threats for your lungs.

The WHO deems up to 50 micrograms of PM 2.5 per cubic meter healthy. In 2017, there were 39 dayswhen readings exceeded 300 micrograms.

As a result, New Delhi schools had to close for days in 2017 because children's lungs are particularly susceptible to air pollution. They also closed in 2016 due to dangerous levels of smog.

In 2015, approximately 1.1 million people died due to air pollution in India, according to the non-profit Health Effects Institute. The WHO reported an average of 4.2 million people die annually from outdoor exposure to air pollution.