The news of fog disrupting rail and air traffic and throwing life out of gear in Delhi and northern India have hit the headlines. Scientists at the Indian Institute of Technology, Kanpur have come out with the reason behind this menace. A study published by them has pointed out that burning agricultural residue is not only detrimental to human health, but also leads to longer spells of dense fog and brings down air quality. While the concentration of oxidised organic carbon that is produced after burning biomass — crop stubble, forest residue and vegetation — is only 9 per cent on non-fog days, it rises to 35 per cent on days that see fog, says the study, according to an Indian Express report. Earlier, NASA images had suggested that burning of crop stubble is considerably impacting the pollution levels.
The study — titled ‘Combined Effects of Organic Aerosol Loading and Fog Processing on Organic Aerosols Oxidation, Composition, and Evolution’ — was published in the peer-reviewed journal, Science of the Total Environment, in August. The study was conducted at Kanpur — one of the most polluted cities in India. The presence of these particles in the air also poses a long-term problem. “If they remain in the air for a longer time, they get oxygenated and become more hygroscopic, leading to more affinity towards water and hence the formation of fog,” said S N Tripathi, co-author of the study. Fog is formed when small water droplets become suspended in the air. The presence of particulate matter gives water droplets a medium to become suspended and aids the formation of fog. Oxidised organic carbon compounds that are formed due to biomass burning also lead to longer spells of fog, Tripathi said. “Once fog is formed, these particles change and attract more water droplets and lead to more fog. This becomes a vicious cycle where one instance of dense fog leads to a second instance of denser fog,” he said.
Delhi and major cities in Uttar Pradesh have been witnessing an unprecedented and prolonged spell of fog for the past two weeks. This is also the first time in six years that fog has descended in the capital so early on in December.
Farmers in neighboring Punjab and Haryana have been setting fire to paddy stubble in their fields after cultivating the crop as part of the slash and burn. A NASA forecast showed high levels of ‘fires and thermal anomalies’ in the Punjab region of India and Pakistan. As per an NYT report, farmers are burning around 32 million tons of leftover straw. The National Green Tribunal had last year told the government to stop farmers from burning their crops. Towards the end of October, farmers begin burning the process of burning paddy stubble which leads to plumes of smoke blackening the skies.
There was “significant” level of stubble burning this year in Punjab and Haryana, however, there is no “conclusive” study to suggest that it “always” impacts quality of air in Delhi, Rajya Sabha was informed. “Available satellite images indicate that the enforcement of ban on paddy stubble burning in farmlands of Punjab and Haryana has not been fully implemented and there has been significant level of stubble burning,” according to a statement which was made in a written reply given by MoS for Environment, Forest & Climate Change Anil Madhav Dave to a query. As per the information furnished, residue from paddy generated by Punjab and Haryana was 19.70 million tonnes and 6.18 million tonnes respectively.
The practice of farmers harvesting the crops by hand is on the decline as most use combines to cut crop, which renders the stubble useless. To get rid of the stubble farmers burn the fields to prepare it for sowing the next crop. Earlier, The National Green Tribunal had slammed the Central government and the state governments of Punjab, Haryana and Rajasthan on the issue of the rising pollution level. Delhi has been covered in a dense layer of smoke ever since Diwali.