The air quality in the national capital turned "severe" on Wednesday, primarily due to low temperature and wind speed, according to officials. However, the pollution levels are likely to decrease slightly on Thursday as a cyclonic circulation is expected to cause light rains and increase the wind speed -- from 6-8 kilometers per hour to 20-30 kmph. On Wednesday, the city recorded its overall air quality index (AQI) at 408 at 4 pm, up from 369 on Tuesday.
The suburbs of Ghaziabad (441), Noida (426), Greater Noida (449), Faridabad (390) and Gurgaon (370) also breathed extremely polluted air. The levels of PM 2.5 -- particulate matter so small that they can enter the lungs and even the bloodstream -- shot up to 257.8 micrograms per cubic metre, more than four times the safe limit of 0-60, by 7 pm.
The last time such levels were reported was on November 16. An AQI between 0-50 is considered 'good', 51-100 'satisfactory', 101-200 'moderate', 201-300 'poor', 301-400 'very poor' and 401-500 'severe'. An AQI above 500 falls in the 'severe plus' category.
Weather department officials said the city recorded a low of 7.9 degrees Celsius, a notch below normal, and a high of 23.2 degrees Celsius. On Tuesday, the mercury had dipped to the season's lowest at 7.4 degrees Celsius.
They said light rain and high-velocity winds are expected in the national capital on Thursday and Friday which will provide relief from pollution. Rains are also likely to occur in neighbouring states of Punjab, Haryana and Rajasthan.
"Wait for another 24 hours. We may get significant relief from Pollution. #Rains will wash away the #Pollutants. Cleaner air to breath from tomorrow evening for #Delhi and NCR," tweeted Mahesh Palawat, a senior scientist at Skymet Weather, a private forecaster.
Dense fog is likely to envelope the city on December 14 and 15 and the mercury is expected to dip to 6 degrees Celsius.