A thick blanket of toxic smog has engulfed most parts of northern India and readings of air quality in the capital New Delhi hit their highest this year after dense fog overnight.
The smog, a toxic blend of smoke and fog, happens each year in winter as cold air traps dust, emissions, and smoke from illegal farm fires in some surrounding states.
Visibility on Monday dropped to 100 metres (109 yards) but authorities said flights and trains continued to operate with some delays.
India’s pollution control authority said the national capital territory’s 24-hour air quality index (AQI) reading was at 484, classified as “severe plus”, the highest this year.
According to Swiss group IQAir’s live rankings, New Delhi was the most polluted city in the world with the air quality at a “hazardous” 1,081 and the concentration of PM2.5 – particulate matter measuring 2.5 microns or less in diameter that can be carried into lungs, causing deadly diseases and cardiac issues – at 130.9 times the World Health Organization’s recommended levels.
Experts say the scores vary because of a difference in the scale countries adopt to convert pollutant concentrations into AQI, such that the same quantity of a specific pollutant may be translated into different AQI scores in different countries.
Authorities directed all schools in Delhi to move classes online and tightened restrictions on construction activities and vehicle movements, citing unfavourable meteorological conditions and low wind speed.
Farm fires – where stubble left after harvesting rice is burned to clear fields – have contributed as much as 40% of the pollution in Delhi, SAFAR, a weather forecasting agency under the Ministry of Earth Sciences has said.
Satellites detected 1,334 such events in six states on Sunday, the most in the last four days, according to India’s Consortium for Research on Agroecosystem Monitoring and Modeling from Space.
India’s weather department has forecast “dense to very dense fog” for the northern states of Uttar Pradesh, Haryana and Rajasthan for Monday.