NEW DELHI (AP) — A thick layer of toxic smog enveloped India’s capital on Friday Smoke from fireworks used to celebrate Diwali Hindu festival of lights, Air pollution has reached dangerous levels.

According to SAFAR, India’s main environmental monitoring agency, New Delhi’s air quality index fell into the “severe” category. In many areas, levels of deadly particulate matter reached seven times the World Health Organization’s safe limit.

Authorities in the capital have banned the use and sale of traditional fireworks since 2017, urging people to opt for eco-friendly fireworks or light shows instead, but the rule is often flouted.

New Delhi, home to more than 33 million people, is regularly ranked as one of the most polluted cities in the world.

The air pollution crisis worsens especially in winter, when burning of crop residues in neighboring states coincides with cooler temperatures that trap deadly smoke. This smoke enters New Delhi, causing an increase in pollution and worsening the public health crisis.

Emissions from industries without pollution controls and the use of coal, which produces most of the country’s electricity, are also linked to poor air quality in urban areas.

“We may not realize it now, but later we will face lung problems,” said Manoj Kumar, a New Delhi resident who does his morning runs around the capital’s famous India Gate monument.

Several studies estimate that more than a million Indians die from air pollution-related diseases every year. Tiny particulate matter in polluted air can lodge deep in the lungs and cause a variety of serious health problems.