Smog fell over the Indian capital on Wednesday, with dense fog and low visibility levels underlining worsening air pollution.

One monitoring station in Delhi showed levels of 1,008 micrograms for particulate matter of less than 10 micrometers in diameter on Wednesday afternoon, well over the World Health Organization’s guideline of 50 micrograms per cubic meter when averaged over 24 hours. Readings at the same station had earlier reached 1,500, according to data from the Delhi Pollution Control Committee.

“Definitely it’s the worst it’s ever been,” Sunita Narayan, director-general of New Delhi-based advocacy group Center for Science and Environment told the Financial Times. “But Delhi’s air has been getting worse every year”.

Studies have shown that India’s problem surpasses China’s air pollution, with air quality having deteriorated steadily over the past decade. Burning of rice straw and diesel fumes have contributed to air pollution, which has been exacerbated by lack of wind to blow the smoke away and high levels of moisture.

“Current levels of air pollution are high and extremely toxic,” according to a CSE statement. “Already there is evidence of severe respiratory ailments afflicting people”.