• Agricultural fires are to blame for about half of the pollution experienced in Delhi in October and November, a peak stubble burning season in Punjab, a Harvard study has found using satellite data from NASA.
• Many farmers in northwest India typically burn abundant crop residue on the fields after harvest season, to prepare their fields for subsequent planting.
• While crop burning has been illegal for years, there has not been a large enough deterrent to effectively crack down on the practice, in part because it’s been difficult to measure exactly how much smoke from the fires is making it downwind to the city.
What the reason
• During the post-monsoon season, the air in northern India is particularly stagnant, meaning smoke particles do not vent into the atmosphere as they would during other times of the year.
• Instead, the black carbon and organic particulate matter slowly permeates throughout the entire region, which is home to 46 million people.
• In urban areas, that smoke mixes with existing pollution from cars and factories creating a thick, deadly haze.
• On average, without fires, urban Delhi experiences about 150 microgrammes per cubic metre of fine particulate air pollution.
• The WHO puts the threshold for safe air at 25 microgrammes per cubic metre, and India’s Central Pollution Control Board limits exposure to 60 microgrammes per cubic metre.