‘Method to measure impact of farm fires not foolproof’

NEW DELHI: The projection of the impact of emissions from crop residue burning in neighbouring states of Haryana and Punjab on Delhi’s air by the union government’s pollution forecasting wing might not be “foolproof”, said a National Environmental Engineering Research Institute (NEERI) scientist on Tuesday. However, the System of Air Quality and Weather Forecasting and Research (SAFAR), which releases a daily bulletin of the estimated share of biomass burning, said its predictions were “nearly accurate”.

S K Goyal, senior principal scientist and head, NEERI-DELHI, said, SAFAR’S prediction of the effect from stubble burning on the air quality in Delhi may not be reliable as multiple methodologies are required to assess the impact. “The forecast may not be foolproof as a number of factors need to be studied on ground to make an assessment of the impact of fire counts on the levels of particulate matter (PM) in Delhi. For instance, one has to look at more evidences on ground such as the volume of the smoke and the area burnt,” said Goyal.

Also, he said, there is some dispersion even as the smoke travels to Delhi. “A prediction of the number of fire counts to take place in the future and an assessment based on it could have errors,” said Goyal, speaking during the launch of a NEERI portal– Indair – a digitalised repository of air quality studies published in the country.

SAFAR, a weather and air quality monitoring unit of the Ministry of Earth Sciences (MOES), releases the estimated share of particulate matter (PM) from the smoke from stubble burning to Delhi’s overall PM 2.5 concentration, which is one of the most prominent pollutant in the national capital region.

Scientists from SAFAR, however, said data from at least two Indian satellites and two US satellites are used for monitoring and forecasting pollution from stubble burning.

“We have developed a highemission inventory of agriculture stubble burning in Punjab and Haryana by objective evaluation of satellite fire counts reconciling with ground realities. Emissions are validated by various methods. The share of biomass burning in the deteriorating air quality in Delhi in 2018 varies from 1% to 58%,” said a senior SAFAR scientist, who refused to be quoted.

He added, “Even though the number of fire counts in Haryana and Punjab was the highest over the past two days, it did not affect Delhi air as much because of good winds that dispersed the pollutants.”

SN Tripathi, head of the civil engineering department at IIT Kanpur said there can be uncertainties in any model-based forecasting methodology. “For instance, in the emission inventory, distribution of fires and its chemistry. If the model is not able to quantify what each fire is emitting in terms of gases and particulate matter, the prediction may have cumulative errors,” he said.

The smoke from stubble burning in Haryana and Punjab contributes to the overall pollution levels in the city. This year, it went up to 46% on October 31, the season’s highest, pushing the air quality index to 410 in the ‘severe’ zone . On Wednesday, however, as per the SAFAR bulletin, the effect from stubble burning in Delhi’s air was estimated at 3% and the AQI was 214.