What's the source of Delhi's winter pollution? 60% from external sources, says study
When the restrictions were in places like ban on entry of trucks, construction and demolition activities and others, air quality did not descend into the 'severe plus' category.
Around 64 per cent of Delhi's winter pollution load comes from outside the capital's boundaries, with "burning of agricultural waste" and "burning for heating and cooking needs" being the major sources, according to a study released on Thursday.
Transport (12 per cent), dust (seven per cent), and domestic biomass burning (six per cent) are the major sources of locally-generated pollution in the city in winter (October 15 - January 15), the study by Council on Energy, Environment and Water (CEEW) said.
The researchers used data from publicly available air quality forecasts, including Delhi's Air Quality Early Warning System (3-day and 10-day), Decision Support System for Air Quality Management in Delhi (DSS), and UrbanEmissions.Info.
"Sixty-four per cent of Delhi's winter pollution load comes from outside its boundaries. Biomass burning of agricultural waste during the stubble burning phase and burning for heating and cooking needs during peak winter are the major sources of air pollution from outside the city, according to UrbanEmissions.Info," the study said.
Data gathered from UrbanEmissions.Info showed that open fires (31.68 percent), dust (15.84 percent) and transport (11.88 percent) were the major sources of pollution in the "stubble burning" phase between October 15 and November 15 last year.
In the "post-stubble burning" phase from November 15 to December 15, use of biomass for household heating and cooking (17 percent), dust (17 percent) and transport (16 percent) contributed the most to the air pollution in the capital.
Interestingly, use of biomass for household heating and cooking (31.68 percent) emerged as the major contributor in the peak winter phase between December 15 and January 15, followed by dust (15.84 percent) and transport (14.85 percent).
The researchers called for surveys in residential areas across NCR to explore the prevalence of biomass usage for heating and cooking purposes.
"Based on this, a targeted support mechanism is required to allow households and others to use clean fuels for cooking and heating. There is also a need to assess and promote alternatives for space heating," they said.
This study also assessed actions taken to tackle winter pollution last year.
In November-December 2021, apart from the Graded Response Action Plan (GRAP) coming into effect in Delhi-NCR, the Commission for Air Quality Management introduced several emergency response measures through a series of directions and orders.
The Supreme Court also stepped in from time to time to direct the authorities to act on air pollution. The first set of restrictions was put in place on November 16, and all were lifted by December 20, barring the one on industrial operations, it said.
While air quality forecasts picked up the pollution trends, they are not yet very accurate in predicting high pollution episodes ('very poor' and 'severe' air quality days), the researchers noted.
When the restrictions were in place like ban on entry of trucks, construction and demolition activities and others, air quality did not descend into the 'severe plus' category, they said.
"The air quality improved from 'severe' to 'poor' when all the restrictions were in place simultaneously, aided by better meteorology. However, when the restrictions were finally lifted, the air quality spiralled back into the 'severe' category resulting in the longest six days 'severe' air quality spell of the season," the study said.
The research team suggested that GRAP implementation must be based strictly on modelled source contributions obtained from forecasts and timed accordingly.
"This will eliminate the need for ad-hoc emergency directions to restrict various activities. For instance, restrictions on private vehicles can be brought in when the air quality is forecasted to be 'very poor' as transport is a significant contributor," they said.
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