A layer of smoky haze shrouded Delhi as its air quality deteriorated to the upper end of the “very poor” category on Tuesday due to calmer winds.

The air quality is forecast to become worse over the next two days due to unhelpful meteorological conditions. Favourable wind speed — 15 to 20 kilometre per hour — is predicted to bring a considerable improvement from November 11.

The capital’s 24-hour average air quality index worsened from 354 on Monday to 372 on Tuesday. It was 339 on Sunday and 381 on Saturday.

An AQI between 301 and 400 is considered “very poor”, and 401 and 500 “severe”. Farm fires in Punjab dropped from 2,487 on Monday to 605 on Tuesday.

Their share in Delhi’s PM2.5 pollution dipped from 14 per cent on Monday to 9 per cent on Tuesday, according to data from the Indian Agricultural Research Institute and SAFAR, a forecasting agency under the Union ministry of earth sciences.

The haze during the day lowered visibility to 800 meters and 900 meters at the Safdarjung and Palam airports, respectively, an official at the IMD said.