Crop residue burning contributes to secondary particulate matter: Study

Air quality monitoring for PM 2.5 was carried out at four sites (Rohini, Okhla, Dwarka, Vasant Kunj) in Delhi in November and December of 2013

NEW DELHI: Crop residue burning in October and November contributed to around 31% of PM 2.5 concentrations (in the range of 15% to 47%) in Delhi and around 21% in the range of 6% to 36% in Kanpur during those months in 2013 and 2014, according to a new research paper.

Burning of crop stubble in Punjab and Haryana is a major cause of smog. (HT Photo/File)

The paper by Indian Institute of Technology (IIT) Kanpur scientists Pavan K Nagar and Mukesh Sharma was published in Elsevier journal on January 5. It used a Weather Research and Forecasting model coupled with Chemistry and another hybrid chemical transport model to study the impact of crop residue burning from October to November in 2013 and 2014. During the study period, the contribution of crop residue burning to PM 2.5 concentration was on an average 72 micrograms per cubic metres in Delhi and 48 micrograms per cubic metres in Kanpur. The average PM2.5 concentration was 246 micrograms per cubic metres (in the range of 117 to 375) in Delhi and 229 micrograms per cubic metres (in the range of 115 to 343) in Kanpur during October and November.

Air quality monitoring for PM 2.5 was carried out at four sites (Rohini, Okhla, Dwarka, Vasant Kunj) in Delhi in November and December of 2013. In Kanpur, it was carried out at IIT during November–December (2013) and October to December in 2014.

Delhi and Kanpur are among the cities directly affected by crop residue burning in places such as Punjab and Haryana

“One of the significant findings of this study is that crop residue burning contributes to secondary particulate matter. We found that vapours and gases like sulphur dioxide, nitrogen dioxide, non-methane hydrocarbons and non-methane volatile organic compounds convert to particulate matter through photochemical reactions as they travel through the Ganga basin. This is why their contribution to PM 2.5 concentrations is high. Normally we only account for primary particulate matter emissions from crop residue burning,” said Sharma. “The paper also highlights how the gases and particulate matter from crop residue burning can travel long distances up to Kanpur.”

In India, the crop residue burning emissions decreased by 1.5% in 2015 and 3% in 2020 compared to 2010, according to a study referred to in the paper. Crop residue burning periods in India are April–May (Rabi crop) and October–November (Kharif crop).

In Punjab and Haryana, paddy residue is burned during October and November and causes a dramatic increase in air pollution levels.

“We also found during our analysis that contribution from crop stubble fires during October and November to PM 2.5 concentrations was 25 to 30%. But it varies a lot depending on weather conditions and number of fires,” said VK Soni, who heads India Meteorological Department’s environment and research centre.