COURTESY HT OCT 17

Behind Delhi’s bad air: Early stubble fires and weather
Jayashree Nandi

letters@hindustantimes.com

New Delhi : 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. A ventilation index below 2,350 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 8,800 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 3,515 fires in Punjab and Haryana, almost three times the 1,217 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 648,000 ha to only 427,000 ha, Gargava said.