Winds clean air up, give Capital its cleanest post-Dussehra AQI

The improvement in the air quality came just a day after pollution in Delhi hit its highest level in over 100 days, prompting authorities to initiate the first stage of the Graded Response Action Plan (Grap), which prescribes measures to keep pollutants under control.

Delhi’s pollution levels dropped sharply on Thursday, on the back of strong winds that gave the city its cleanest post-Dussehra air since at least 2015, when the air quality index (AQI) was introduced.

People watch the burning of effigies of demon king Ravana and his son and brother in New Delhi, India, (AP Photo/Altaf Qadri)

The improvement in the air quality came just a day after pollution in Delhi hit its highest level in over 100 days, prompting authorities to initiate the first stage of the Graded Response Action Plan (Grap), which prescribes measures to keep pollutants under control.

The city on Thursday clocked an AQI of 79 (categorised as “satisfactory”), according to the Central Pollution Control Board’s (CPCB) 4pm bulletin, a huge improvement from 211 on Wednesday. This, experts said, was largely because wind speeds picked up on Wednesday, and hovered between 20 and 30km/hour on Thursday as well.

Delhi is likely to get some rain on Friday and the weekend, according to forecasts by the India Meteorological Department (IMD), which initially predicted showers from October 5. (HT Illustration)

Data from CPCB shows that last Dussehra, Delhi’s AQI was 198 (moderate) on October 15. However, emissions from effigy burning led this to worsen to 284 (poor) the next day. In 2020, Delhi’s AQI on Dussehra (October 25) was already very high — hovering at 349 (very poor), increasing marginally to 353 (very poor) the next day.

The lowest AQI recorded in Delhi the day after Dussehra was in 2019, when it was 173 (moderate), data shows. Back then, it rose from a reading of 112 (moderate) on Dussehra day (October 8), shows data.

Rain may help keep Delhi’s air clean

Delhi is likely to get some rain on Friday and the weekend, according to forecasts by the India Meteorological Department (IMD), which initially predicted showers from October 5.

However, officials said, the weather system slowed down and is now expected to bring Delhi rain from October 7.

“The low-pressure area is slowly advancing from the Bay of Bengal and has reached Uttar Pradesh already. Delhi is expected to see light rain from Friday onwards,” said the official.

Mahesh Palawat, vice president at Skymet meteorology, a private weather forecaster, said the intensity of rain will increase from October 8, with stronger spells expected between October 8 and 10.

“There are also chances of moderate rainfall during these three days. Rains are expected between October 11 and 13 too, but they will get less intense. After October 13, dry northwesterly winds will once again make a return,” he said, stating the same weather system, which had reached UP, was sending strong easterly winds to Delhi.

“These winds have led to an increase in local wind speed, which is around 15-30 km/hr and has led to an improvement in air quality,” he said.

On Wednesday, Delhi’s air quality hit its worst levels since June 25 this year. This led to an emergency meeting, with the first stage of Grap being put into place.

Grap measures likely to stay for now: Officials

Officials said the measures will remain, unless another review meet is held to revoke them.

“Until they are withdrawn, they will remain and will help maintain cleaner air. Despite rain expected in the coming days, action will continue on the ground,” an official, part of the CAQM subcommittee said.

Forecasts by the Early Warning System (EWS) for Delhi — on which CAQM relies for its forecasts, said Delhi’s AQI could remain ‘satisfactory’ from October 7 until 9.

“The predominant surface wind is likely to be coming from the east into Delhi with wind speeds upto 15km/hour, with generally cloudy skies and light rain expected on Friday. Wind speeds will be around 15-16 km/hr on Saturday with light to moderate rain expected, while light to moderate rain activity with an average wind speed of 16 km/hour is also expected on Sunday,” the EWS forecast said.