NEW DELHI: A thick layer of haze enveloped the national capital on Thursday, as the city’s air quality remained in the ‘severe’ range for the third consecutive day. Winds dying down, high humidity levels allowing pollutants entrapped too close to the earth’s surface led to the pollution levels remaining high, said scientists and weather officials monitoring air quality.
As per the Central Pollution Control Board (CPCB), Delhi’s overall air quality index (AQI) was 423 in the severe zone. It was 407, the previous day and 402 on Tuesday. The pollution episode started with winds slowing down because of an approaching Western Disturbance (WD) and likely to remain so on Friday as well, said weather officials at India Meteorological Department (IMD).
IMD officials said at present easterly winds, carrying a high moisture load, are blowing over Delhi. “These winds are calm and with high humidity. This is only helping in the accumulation of pollutants, while no dispersion is happening. This continuous accumulation without any ventilation has kept air quality in the ‘severe’ zone. Without any scope of circulation, pollutants settle too close to the ground, forming a thick layer of haze,” said a senior official.
On the brighter side, officials said that two more WDs on December 24 and 26 are likely to induce good showers during December 26-29, which may wash out the pollution. This is not just Delhi’s but the northwest region’s pollution, which is settling in Delhi. “A WD moving from J&K will impact the entire northern plains. When rain occurs, it will clean up the whole region and improve air quality,” the official said.
RK Jenamani, senior IMD scientist, said, “A fresh intense WD and its induced cyclonic circulation are likely to influence northwest India from December 26. Under its influence; light to moderate, scattered to fairly widespread rainfall is very likely over Punjab, Haryana, Chandigarh, Delhi and UP.”
The successive WDs have resulted in a rise in temperatures from previously existing cold wave conditions. On Thursday, the minimum temperature was 5.5 degrees C, two notches below normal. The maximum settled at 23.1 degrees C, two notches above normal for this time of year.
The Ministry of Earth Sciences’ early warning system on Thursday said, “AQI is in ‘severe’ category due to low ventilation and pollutant entrapped below 900 mbar with up to 50 per cent relative humidity. Similar conditions will prevail on December 24. An increase in ventilation and mixing height will result in likely improvement in AQI from December 25,” it said.
