The reason for Delhi’s air quality to worsen over the past week is adverse meteorological conditions and the early start of stubble burning, mainly in Punjab, officials from the Central Pollution Control Board (CPCB) said on Friday.
The silver lining? The peak of stubble burning may not coincide with the worst meteorological conditions .
Last year, in September and October (till October 14), there were seven rainy days that brought around 121 mm rain. This year, there have been only three rainy days in the same period, and they have brought only 21 mm rain. The average ventilation index in this period has been 1389 square metres/s, with a low of 636 sq m/s. The ventilation index is a function of the mixing height and the wind speed and defines the ability of the atmosphere to disperse contaminants. A ventilation index below 2350 sq metres/second is considered poor. The mixing height is the height at which the pollutant mixes in the air.
On Friday, the contribution of stubble burning to Delhi’s PM 2.5 (particulate matter 2.5 microns or smaller in width) concentration was 11% according to CPCB, perhaps a function of the exceptionally high ventilation index of 8800 sq m/s.
At its peak, stubble burning accounts for almost half of Delhi’s pollution. Last year, this was 44% on October 31.
Prashant Gargava, member secretary, CPCB said that because the harvest of the kharif (monsoon) crop and stubble burning started earlier than normal this year, the peak of the fires may not coincide with the most adverse meteorological conditions in Delhi.
Indeed, according to the India Meteorological Department, the harvest season till October 15 this year has seen 3515 fires in Punjab and Haryana, almost three times the 1217 in the same period last year, and five times the 773 fires recorded in 2018.
“This year because stubble fires have started relatively early we are hoping that the peak contribution from fires reduces by the time minimum temperature starts falling significantly and before Diwali,” said Gargava. Diwali will be celebrated on November 14 this year. Diwali was celebrated on October 27 last year.
Interestingly, contribution from stubble fires may also be lower this year this year because the area under non-Basmati paddy (which leaves stubble that needs to be disposed) has reduced in both Haryana and Punjab this year after a very long time according to officials. In Punjab, the area under non-Basmati paddy has reduced from 2.291 million hectares (ha) to 2.076 million ha this year; in Haryana the area has reduced from 648000 ha to only 427000 ha, Gargava said.
“This year around 400000 ha non-Basmati area has gone to other crops like cotton and maize according to our assessment. Out of 2.076 million ha area under non-Basmati in Punjab only 482000 ha is under under long duration variety Pusa 44 this year. This means that most farmers grew short duration paddy variety and had more time to dispose stubble. We are hopeful that stubble fires will be lower this year. Our concerns are that there should be efficient use of the straw management machines that have been distributed,” ,” said Trilochan Mohapatra, director general, Indian Council of Agricultural Research.
To be sure, data on the number of straw management machines distributed this year, compared to last year, and the use of these machines isn’t available. The increase in fires to data would seem to suggest that enough of these machines are not being used.
Mohapatra added that “another apprehension is that because of attention of farmers going to farm bill agitation, they may be resorting to burning stubble”.
Elaborating on CPCB’s plans for the winter, Gargava said field inspections will be carried out from October 15 to February 28—a period of nearly five months. Industries and construction agencies will have to provide an undertaking for adhering to prescribed environmental norms such as keeping dust down, covering the construction space etc. Delhi Pollution Control Committee will also deploy inspection teams.
Gargava said that there is around 20% reduction in annual PM 2.5 concentrations from 2016 to 2019 and 25% reduction in PM 10 concentrations.