The air pollution in Delhi may reach 20 times higher than the safe limits owing to agricultural fires during peak burning season, a team of researchers has warned.
During October and November - the peak burning season in Punjab - about half of all pollution in Delhi can be attributed to agricultural fires on some days, the study published in the journal Environmental Research Letters informed.
"On certain days during peak fire season, air pollution in Delhi is about 20 times higher than the threshold for safe air as defined by the World Health Organization (WHO)," said first author Daniel H Cusworth from Harvard John A Paulson School of Engineering and Applied Sciences in Cambridge, Massachusetts.
To model how much of that pollution is coming from the fires, the researchers used satellite data from NASA to identify hotspots corresponding to active fires.
The team gathered available data for October and November, 2012 to 2016 and plugged it into a particle dispersion model -- an algorithm that accounts for geography, wind patterns, and physics to predict how far and in what direction smoke particles travel.
During the post-monsoon season, the air in northern India was particularly stagnant, implying that smoke particles don't 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," the paper highlighted.
On average, without fires, urban Delhi experiences about 150 micrograms per cubic metre of fine particulate air pollution.
WHO puts the threshold for safe air at 25 micrograms per cubic metre and country's Central Pollution Control Board (CPCB) limits exposure to 60 micrograms per cubic metre, added Cusworth and senior research fellow Loretta J Mickley.
Extreme fires during the post-monsoon season can pump on average about 150 micrograms per cubic metre of fine particulate matter into the city, doubling the amount of pollution and increasing total levels 12 times higher than WHO recommendations and even 20 times higher on some days, the researchers said.