Stubble fires that continued to burn in northern India, aided by north-westerly winds that blew the fumes in Delhi’s direction, worsened air pollution in the capital at the weekend. Over 1,000 fires, the highest for the season, had been recorded on Saturday by the air quality early warning system of the ministry of earth sciences (MoES).
But an estimate of the contribution of stubble fires to Delhi’s particulate matter (PM )2.5 level wasn’t updated on Sunday by the MoES. The System of Air Quality and Weather Forecasting Research (SAFAR) model under the Indian Institute of Tropical Meteorology (used by the Central Pollution Control Board for pollution analysis) showed 17% contribution to Delhi’s PM 2.5 load on Sunday. It was 18% on Saturday; MoES data showed that stubble fires contributed 22% to pollution in the capital on Saturday.
The highest number of fire points of the season were observed over Punjab (966), Haryana (167) and UP (38) on Saturday which are likely to have an adverse impact on air quality of the national capital (NCR) region centred on Delhi, the MoES website said. The impact was restricted because of better mixing height, the height at which pollutants mix in the air, and ventilation.
Contribution of stubble fires to PM2.5 pollution is likely to rise on Monday and Tuesday. On Friday and Saturday, the MoES website had shown that the fires contributed 11% and 22% to Delhi’s PM 2.5 load.
“We are assessing the performance of the model. The forecast based on models for fire contribution will be updated,” said Sachin Ghude, scientist at the India Meteorological Department (IMD).
Wind direction remained north-westerly on Sunday, with calm winds until 8 am and then moderate winds of 13 to 15 kmph in the afternoon. The minimum temperature on Sunday night was 16.6 degrees C, 2 degree C below normal.
“Wind direction is north-westerly and will remain so for the next two to three days. Wind speed is picking up in the afternoon, going up to 15 kmph but nights are calm so dispersal of pollutants is impacted,” said Kuldeep Shrivastava, head of the regional weather forecasting centre of the IMD.
The ventilation index on Sunday was around 11500 m2/s. The ventilation index is a function of the mixing height and the wind speed and defines the ability of the atmosphere to disperse contaminants. A ventilation index below 2,350 sq metres/second is considered poor. Mixing height is the height at which pollutants mix in the air.
Additional chief secretary (development) Anirudh Tiwari said action was being taken immediately to extinguish fires when any are noticed. In Gurdaspur district of Punjab, for example, 50 squads have been formed, each squad consisting of four to six persons has been allocated 30 villages.
“The squad visit all 30 villages daily from 2 to 6pm. As pre-emptive action, fires are extinguished as soon as they are detected using fire brigades or tractors,” he said.
“As per our analysis, fire points are increasing and wind direction is also north-westerly but local surface winds in Delhi are not letting the contribution from fires increase to severe levels,” a senior CPCB official said on condition of anonymity.