The national capital and its adjoining suburbs were blanketed in a grey haze on Wednesday morning, dipping visibility to 300 meters at some places, causing train delays and slowing down flight operations here.

Some 30 trains coming to Delhi and 30 flights landing or taking off from the Delhi airport were delayed, according to officials.

The air quality in Delhi and adjoining Noida (Uttar Pradesh) and Gurgaon (Haryana) continued to be alarmingly bad on Wednesday.

Due to worsening air pollution, authorities closed schools on Wednesday and Thursday.

The situation prompted Delhi Chief Minister Arvind Kejriwal to write on Twitter: “Delhi has become a gas chamber. Every year this happens during this part of the year. We have to find a solution to crop burning in adjoining states.”

The average air quality index was 477 and the level of dangerous PM2.5 particles was “severe” at 475 microgrammes per cubic metre — about 19 times more than permissible globally.

The permissible range for PM2.5 is 60 as per Indian standards and 25 globally.

The “severe” level has prompted an advisory from the Ministry of Earth Science, cautioning against outdoor activities.

“Give a miss to walk today. Stop any activity level if you experience any unusual coughing, chest discomfort, wheezing, breathing difficulty or fatigue and consult a doctor. Masks known as N-95 or P-100 respirators may only help if you go out,” advised SAFAR-India, the ministry-run air quality and weather forecasting research centre.

According to data from the Environment Pollution Prevention and Control Authority (EPCA), the air quality in Noida, Gurgaon and Faridabad (Haryana) was just as bad, with the presence of PM 2.5 NCR pegged at 445 till 10 a.m.

The level of PM2.5 in Noida Sector 125 was especially steep (525). In Faridabad Sector 16, it was 452 by 10 a.m.

In Vikas Sadan at Gurugram, the level of PM2.5 was 316 — lowest of all those observed till then.

According to the Indian Meteorological Department (IMD), visibility dropped to 300 meters at many places in the capital.

Poor visibility also caused heavy traffic snarls at many places in Delhi and NCR. The saving grace was the absence of hundreds of school buses on the roads.

“There was moderate to dense fog in the morning. The sky will remain mainly clear ahead,” said an IMD official. The humidity at 8.30 a.m. was 98 per cent.

Tuesday’s maximum temperature settled at 30.2 degrees Celsius, one degree above season’s average. The minimum was recorded at 16.2 degrees Celsius, three notches above the season’s average.

The situation is likely to worsen on Thursday as the weather department predicted “dense to very dense fog very likely” at many places in Punjab, Haryana, Chandigarh, Delhi, Rajasthan and western Uttar Pradesh.