Strong winds bring pollution levels down, minimum temperature up in Delhi
Delhi's air pollution improved from "very poor" to "poor" due to strong surface winds, but is predicted to worsen again as wind speeds drop.
After 12 straight days of “very poor” air, Delhi’s pollution levels improved to the “poor” category as strong surface winds led to the city recording a 24-hour average air quality index (AQI) reading of 286 on Tuesday, according to the Central Pollution Control Board’s national bulletin released at 4pm — down from 330 (very poor) the day before.
However, the India Meteorological Department (IMD) has predicted a drop in wind speed from Wednesday, and forecasts by the Early Warning System (EWS) for Delhi, a forecasting model under the ministry of earth sciences, show the air quality is likely to return to “very poor” once again.
“We recorded surface winds touching up to 15 kmph on Monday evening, and it touched a speed of 18kmph during the day on Tuesday,” said Kuldeep Srivastava, scientist at IMD, stating wind speed will go below 10 kmph by Wednesday.
Delhi’s AQI was last in the ”poor” zone on December 6, when it was 286. Delhi is yet to record a ”severe” air day since November 24, when the AQI was 415.
Delhi’s minimum temperature, meanwhile, was 7.8 degrees Celsius (°C) — around normal for this time of the year, but a slight rise from the 7.1°C on Monday. Due to the impact of a western disturbance in the Himalayas, Delhi’s minimum has been rising since Friday, when the Capital recorded a season-low of 4.9°C, which then rose to 5.5°C on Saturday, and 6.5°C on Sunday.
A western disturbance usually leads to a change in wind direction, to warmer southeasterly winds. It also brings moisture and cloudiness, which makes nights warmer as the clouds are able to trap the heat the surface captured during the day.
“The wind direction is still northwesterly, but in order for the minimum to dip, generally, clear skies and calm winds are needed,” Srivastava said.
Delhi’s maximum was 23.5°C on Tuesday, a degree above normal. It was 22.3°C on Monday.
According to IMD forecasts, Delhi’s minimum temperature is likely to hover around the 7-degree mark for the next three days, with another western disturbance set to approach the capital from December 22. “The next western disturbance will start impacting from December 22 onwards and there will be cloudiness across the plains. This will not allow minimum temperature to drop,” Srivastava said, adding that shallow fog should persist over Delhi over the next six days.