The levels of PM10 shot through the roof in most parts of Delhi Tuesday morning with strong winds raising dust.
India Meteorological Department (IMD) scientists have attributed the situation to low rainfall resulting in dry soil over the region and gusty winds prevailing, along with heating over the past few days with temperatures remaining above 40 degrees Celsius.
IMD scientist Kuldeep Srivastava said the wind speed was around 48 kmph at around 3-4 am Tuesday, which came down to around 15 to 16 kmph later in the morning. Explaining the morning’s phenomenon, Srivastava said high temperatures result in dry soil and since there has not been any rainfall recently, this loose soil was suspended in the air because of strong winds. The maximum temperature in Delhi has remained above 40 degrees Celsius for the past four days.
On what is bringing the strong winds to Delhi, Srivastava said a western disturbance has been affecting Northwest India, though it has not brought any significant rainfall to the national capital. “This (dust raising winds) happens sometimes in this season,” Srivastava said.
The dust also lowered visibility at the IGI Airport to around 1,100 metre on Tuesday morning, which is down from 4,000 metre a day before.
At the monitoring station at Mandir Marg, the PM10 concentration was 1,915 µg/m3 at 9 am, data from the Delhi Pollution Control Committee (DPCC) shows. This is around 19 times the 24-hour standard of 100 µg/m3, and well above the concentration of 160 µg/m3 recorded at 9 pm the previous night. PM10 levels at Mandir Marg crossed the 1000 µg/m3-mark at 6 am on Tuesday.
At the Jahangirpuri monitoring station, the PM10 concentration was 38 times the 24-hour standard at 9 am – 3,826 µg/m3, DPCC data shows. At 6 pm on Tuesday, this level had dropped to 575 µg/m3, which is still more than five times the 24-hour standard.
At Nehru Nagar, PM10 levels shot up to 1,757 µg/m3 at 9 am, from 62 µg/m3 at 2 am on Tuesday.
PM10 is particulate matter with a diameter of 10 micrometers or less, and can be inhaled. Dust in the air can result in high PM10 levels.
PM2.5, which is usually generated by combustion, also saw an increase on Tuesday morning, but levels were not as high as PM10. At Jahangirpuri, the PM2.5 level at 9 am was 374 µg/m3, up from 84 µg/m3 at 7 pm on Monday. Similarly, at Nehru Nagar, the PM2.5 concentration was 190 µg/m3 at 9 am, up from 39 µg/m3 at 5 am on Tuesday. The 24-hour standard for PM2.5 is 60 µg/m3.
High levels of inhalable particulate matter in the air can be linked to respiratory symptoms like irritation of the airways, coughing and aggravated asthma, according to the US Environmental Protection Agency.
The high PM10 level Tuesday morning was reflected in the 24-hour average AQI data for the city. Data from the Central Pollution Control Board shows that the 24-hour average AQI at most monitoring stations in the city was in the ‘very poor’ (301 to 400) or ‘poor’ (201 to 300) categories at 6 pm on Tuesday, with PM10 continuing to be the prominent pollutant at most stations.
The 24-hour average AQI at Anand Vihar was 316, while it was 363 at Shadipur at 342 at Sonia Vihar at 6 pm.
Some parts of the NCR fared worse than Delhi with regard to AQI: Greater Noida (318), Noida (292), and Ghaziabad (296), with PM10 being the prominent pollutant.
A sub-committee of the Commission for Air Quality Management (CAQM) for invoking actions under the Graded Response Action Plan (GRAP) met on Tuesday to consider the air quality situation, but has not invoked any actions. The sub-committee “noted this to be an exceptional episodic event” which is likely to “improve in one-two days”.
The IMD had informed the sub-committee that strong winds raising dust flowed across Haryana and Delhi since early morning on Tuesday, increasing particulate matter concentrations significantly.
A source apportionment study of PM2.5 and PM10 in Delhi-NCR done by The Energy and Resources Institute and the Automotive Research Association of India in 2018 found that dust from roads, soil and construction was the largest contributor to PM10 levels in Delhi in summer, resulting in around 42 per cent of the concentration. The study attributed the higher contribution of dusty sources to PM10 in summer to dry conditions and higher wind speeds.
The maximum temperature recorded on Tuesday was 39.9 degrees Celsius, a notch below the normal.
While partly cloudy skies are likely on Wednesday, when the maximum temperature could be around 41 degrees Celsius, light rainfall is likely on Thursday along with gusty winds of 25 to 35 kmph. The maximum temperature is set to rise further to around 44 degrees Celsius by May 21.
An IMD bulletin issued on Tuesday said that dust raising winds or a dust storm is likely over in isolated pockets of Haryana, Delhi, western Uttar Pradesh and Rajasthan from May 16 to 18.