Flight operations were suspended at the Chandigarh airport on Thursday because of poor visibility in the city after a dust storm. As many as 33 flights arriving at and departing from the airport, including three international ones, were cancelled, The Times of India reported.

Visibility plummeted in cities across North India because of air pollution. The air quality in several parts of the National Capital Region was at dangerous levels in the morning, even as officials said the thick haze is likely to persist till Friday. The concentration of dust particles in the air was two times the level on Tuesday evening.

The level of particular matter PM 10, a major pollutant, has stayed over 500 micrograms per cubic metre for the last 32 hours, according to the Central Pollution Control Board. The level was 800 micrograms per cubic metre on Thursday morning. PM 10 refers to pollutants with particles of sizes 10 microns or lesser.

The Air Quality Index in Siri Fort area was 500 – the maximum possible on the scale used by the pollution control board. An Air Quality Index reading up to 50 is considered “good” and up to 100 is considered “satisfactory”. A reading between 401 and 500 is ranked “severe” on the index, which means the air is dangerously filled with pollutants.

The Air Quality Index in Greater Noida was also 500 at 1 pm.

The “severe” air quality can affect healthy people too, and “seriously impacts those with existing diseases”, according to the pollution control board.

The index was 454 in Aya Nagar and 471 in ITO area.

“Due to the high wind speeds, dust particles are being transported from Rajasthan,” VK Shukla, the scientist in charge of the Air Lab at the Central Pollution Control Board, told Reuters on Wednesday. “The situation is likely to remain the same for the next two days.”

RK Jenamani, head of the aviation meteorology services of Delhi region, told the Hindustan Times: “Such strong winds are expected to continue till Friday night after which they are likely to weaken. There are chances of rain on June 17.”

The air quality in Delhi has deteriorated since Tuesday evening due to a ground-level dust storm in western India.