New Delhi: Residents in northern India awoke to another day of hazardous air quality on Tuesday, with a thick layer of fog blanketing much of the region and pollution levels in Delhi remaining critically high.

Every winter, India grapples with severe air pollution as cold, stagnant air traps dust, emissions, and smoke from illegal crop stubble burning in the agricultural states of Punjab and Haryana. In Delhi, the air quality index (AQI) hit an alarming 491 on Monday, prompting authorities to impose restrictions on vehicle movement and construction while shifting schools to online classes.

By Tuesday, Delhi's AQI stood at 488 on a scale of 500, according to the Central Pollution Control Board (CPCB), with several monitoring stations reporting the maximum possible reading of 500. The CPCB categorizes AQI levels above 401 as "severe," posing a risk even to healthy individuals and severely affecting those with pre-existing health conditions.

Swiss air quality group IQAir ranked Delhi as the world’s most polluted city, with a "hazardous" AQI of 489 on Tuesday. While this was a marked improvement from Monday's shocking 1,081 reading, the disparity highlights variations in how different countries calculate AQI scores based on pollutant concentrations.

The Indian Meteorological Department noted a slight improvement in visibility over Delhi due to a shift in the fog layer toward Uttar Pradesh. However, visibility plummeted to zero in Agra, where the iconic Taj Mahal has remained veiled in toxic smog for nearly a week.

Meanwhile, strict anti-pollution measures have significantly disrupted industrial activity in the region, impacting over 3.4 million small and medium enterprises in Delhi and the neighboring states of Punjab and Haryana, local reports suggest.