Dust-filled skies reduced visibility in the parts of the capital with the concentration of coarser PM10 particles shooting up from around 140 micrograms per cubic metre to 775 micrograms per cubic metre by 8am.
Delhi’s average Air Quality Index (AQI) worsened to the poor category (202) at 11:10 am on Tuesday compared to 162 (moderate) at 4pm on Monday. The AQI was likely to deteriorate as the day progresses.
The India Meteorological Department (IMD) said dust-raising winds were coming from the west and that the dust concentration was expected to gradually reduce as the day progresses. IMD said there were also chances of trace rain in parts of the capital.
IMD scientist Kuldeep Srivastava said strong dust-raising winds over Delhi and National Capital Region (NCR) since 6am reduced the visibility to 1100 metres at Palam. He cited intense heating over the last five days and shooting of the mercury to over 40°C and said this has led to fairly dry soil. “With these winds blowing, we are seeing local dust get lifted…long-range dust is also coming from neighbouring states.”
IMD’s satellite imagery showed the concentration of the dust over Delhi-NCR, western Uttar Pradesh, north Haryana, and parts of Rajasthan.
A second IMD official said the dip in visibility to 1,100 metres on Tuesday morning was considerable as it was around 4,000 metres at the same time on Monday. “This is all dust though and not smog.”
IMD scientist VK Soni, who is part of the Commission for Air Quality Management in National Capital Region and Adjoining Areas, said they were closely monitoring the air quality in real time. “The dust concentration has increased manifold with the PM 10 concentration increasing by four to five times. This is mainly because of strong gusty winds prevailing over the region during the early hours. However, this dust will settle down soon.”
Dust storms in summer are common. Lack of rain over time often makes the topsoil extremely dry. This makes it easier for the dust to get lifted from the surface, even if the wind speed is around just over 10 km per hour.
In summer, long-range dust transportation from Rajasthan to the NCR pushes AQI to very poor or severe categories. The natural barrier in the form of the Aravallis would prevent a large chunk of dust from reaching the capital. It has been weakened as the eco-sensitive region has suffered damage over the years due to illegal-mining.