Delhi air pollution: Stubble burning is the major reason, reveals Harvard study
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.
Agricultural fires are to blame for about half of the
pollution experienced in Delhi in October and No-
vember, 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.
To what extent the large quantity of smoke emitted by
these fires contributes to the already severe pollution
in New Delhi has remained a key question.
For the past few years, every autumn New Delhi –
already plagued with thick pollution – gets engulfed
choking smoke likened by many to a gas chamber.
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. Research-
ers from the Harvard University and NASA have now
shown that in October and November, a peak burning
season in Punjab, about half of all pollution in Delhi
can be attributed to agricultural fires on some days.
“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 Organi-
zation (WHO),” said Daniel H Cusworth, a graduate
student at SEAS and To model how much of that pol-
lution is coming from the fires, the study published
in the journal Environmental Research Letters, used
satellite data from NASA to identify hotspots corre-
sponding to active fires.
The team gathered available data for October and No-
vember, 2012 to 2016 and plugged it into a particle
dispersion model – an algorithm that accounts for ge-
ography, 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 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 organ-
ic 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. To put that into perspec-
tive, 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 micro-
grammes per cubic metre, said Cusworth. Extreme
fires during the post-monsoon season can pump on
average about 150 microgrammes 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.
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