A thick blanket of smog shrouded India’s capital early Monday after firecrackers lit up the skies over New Delhi during Diwali celebrations, compounding dangerously high pollution levels and intensifying the seasonal air pollution crisis that grips the city every year.

Despite restrictions on fireworks, residents in New Delhi celebrated the Hindu festival of lights with firecrackers on Sunday evening, releasing smoke and fine particulate matter into the atmosphere. The Air Quality Index exceeded 350 in several parts of the capital on Monday morning, reaching the severe category and posing significant health risks.

Monitoring stations across the city recorded similarly alarming levels, while visibility deteriorated as a gray haze blanketed streets and high-rise buildings.

India’s Supreme Court in October had sought to limit Diwali pollution by restricting conventional firecrackers and allowing only approved “green firecrackers” under specified conditions for three-hour windows on Saturday and Sunday. The crackers produce fewer emissions but are not pollution-free. They still release particulate matter and other pollutants, adding to the city’s already hazardous air.

New Delhi and its metropolitan region, home to more than 30 million people, regularly rank among the world’s most polluted areas during winter. Pollution worsens as Diwali fireworks coincide with cooler weather and smoke from crop-residue fires in neighboring states of Punjab and Haryana.

After harvesting rice, farmers often burn leftover stalks to clear their fields for the next planting season. The smoke drifts toward New Delhi, adding to pollution from vehicles, industries, construction dust and other local sources.

The problem becomes particularly acute in late October and November, when cooler temperatures, low wind speeds and stagnant atmospheric conditions prevent pollutants from dispersing. The result is a thick haze that can linger over the capital and surrounding areas for days.

Authorities in New Delhi have implemented a set of measures to curb pollution, which include limits on construction activity and restrictions on diesel generators, while courts have sough restrictions on firecrackers. But the measures have not prevented the return of severe pollution each year.

Environmentalists say long-term solutions, such as cleaner energy and stricter controls on vehicle emissions, are needed to prevent the annual crisis.