Why is Delhi-NCR under a thick haze? IMD says dust from Pakistan, strong winds responsible

Delhi-NCR woke up to a thick haze on Thursday after sudden gusty winds and a dust surge swept through the city on Wednesday night. As a result, visibility plunged at many locations, said the India Meteorological Department (IMD).

Due to an incoming cloud mass reported Wednesday night, sudden gusty winds of 30-40 km per hour over the Palam area swept fine dust particles into the lower atmosphere. A senior IMD official said visibility fell from 4,500 m to 1,200 m in under two hours from 10 pm to 11.30 pm.

Although winds later calmed to 3 to 7 kmph, the suspended haze lingered through the night, affecting air quality. According to the official, visibility continued to remain poor at 1,200-1,500 m at both Safdarjung and Palam airports with dust in the air.

At dawn, a westerly breeze of around 10 kmph began to disperse the dust layer, nudging visibility back to 1,500 m at Palam.

Despite the sudden drop in visibility and the heavy load of suspended dust, IMD officials clarified that the phenomenon did not qualify as a duststorm.

According to IMD’s forecast classification, a “light” duststorm requires wind gusts up to 40 kmph and visibility below 1,000 m. In Delhi’s case, while wind speeds briefly peaked, visibility never dropped below the threshold of 1,000 m. The lowest visibility that Delhi reported was 1,200 m on Wednesday night.

IMD officials said dust from North Pakistan travelled through Rajasthan, Punjab and Haryana to reach Delhi-NCR Wednesday night under “the influence of strong lower-level westerly winds”. They said the dust movement gradually towards the east has helped clear up the skies.

A massive dust storm was reported in mid-April, which prompted flight diversions as the city remained under red alert. An intense pre-monsoon storm was also observed on May 2, which uprooted several trees in the region and caused severe damage. Strong surface winds had contributed to the event, among other factors.

According to the Indian Institute of Tropical Meteorology, the Air Quality Index (AQI) at 8 am was 236, or in the ‘poor’ category, in Delhi.

As the AQI clocked at 292 on Thursday, the Commission for Air Quality Management in NCR and Adjoining Areas (CAQM) said that it “took stock of the current air quality scenario and noted that owing to episodic event of dust emanating from the western region of the country, concentrations of PM 2.5 and PM10 have increased significantly which has caused AQI to exhibit a sharp increasing trend… The Sub-Committee attributes the sudden and sharp deterioration in AQI to long-range transport of dust caused by substantial wind speeds, which is purely episodic in nature.”

Noting that “no adverse meteorological factors” are expected as the air quality has been forecast to be in the ‘moderate’ category, the CAQM said it would closely review the situation on Friday.

In its forecast for the next two days, it said, “The air quality is likely to be in the moderate to poor category”.

Meanwhile, IMD has forecast strong surface winds over the weekend. On Friday, respite is likely as IMD has forecast rain with thunderstorms. IMD has also issued a warning for dust storm or thunderstorm activity over isolated places in Haryana and Rajasthan with gusty winds reaching up to 50 kmph.

The weather department also said that there will be no heatwave conditions during the week.