Delhi's 'severe' smog hours tripled after Punjab-Haryana groundwater policy came into force: Study

New Delhi, Dec 4 (PTI) A new study has found that the number of hours when Delhi recorded air quality in the “severe” category has tripled since 2010, with the shift in stubble burning timing due to the 2009 Groundwater Conservation Policy implemented by Punjab and Haryana.

The 2009 Groundwater Conservation Policy in Punjab and Haryana delayed paddy sowing, shortening the harvest and planting cycle and forcing farmers to burn crop residue in early to mid November instead of late October.

The study, 'The role of atmospheric feedback and groundwater conservation policies in degrading air quality in Delhi', says the shift raised the daily 4 pm air quality index (AQI) by around 90 points and increased the number of "severe" hours by 275 per cent -- rising from 89 hours to 334 hours after the change in burning patterns.

According to the research conducted by the Indian Institute of Tropical Meteorology, the National Centre for Atmospheric Research in the United States and the Commission for Air Quality Management, the timing shift in burning of crop residue intensified Delhi’s exposure to crop fire smoke during a period of naturally poorer atmospheric ventilation.

According to the study, this new burning window coincides with cooler temperatures, weaker winds and a much lower boundary layer, conditions that trap pollution near the surface.

The research notes that this shift in burning timing contributed to a significant rise in daily average PM 2.5 levels in Delhi. The study reports that in the post-2010 scenario PM 2.5 levels increased by about 60 micrograms per cubic metre, which is an increase of 36 per cent compared to the pre-2010 period.

The researchers examined Delhi’s air quality during the stubble burning season for five years from 2017 to 2021 using a high resolution atmospheric model.

They compared the post-groundwater conservation policy timing, when fires occur in early to mid November, with a scenario where fires were shifted 15 days earlier as they did before 2010, the study said.

The model used weather data, fire emissions and ground level particulate measurements to assess how the timing change and local conditions influenced pollution levels in Delhi, it added.

According to the study, the transport of smoke from Punjab and Haryana continues to be a major driver of Delhi’s pollution, with northwesterly winds carrying emissions from farm fires into the Indo-Gangetic Plain.

The paper notes that on some days PM 2.5 levels in affected regions touched 600 micrograms per cubic metre, with Delhi lying directly downwind of this flow of emissions.

The research also estimates a substantial health burden linked to the policy driven shift in burning dates.

According to the study, the change added an estimated 205 additional individuals to the short term excess health burden during October and November 2021.

Short-term excess health burden refers to the number of additional people who may face health impacts or premature mortality because of sudden spikes in pollution over a short period.

It further estimates 9,978 additional years of life lost, within a range of 8,323 to 11,682. The total short term excess health burden in that season was 2,122 individuals, the study reports.

According to the institutions behind the study, aerosol radiative feedback alone accounts for about 40 percent of the increase in severe pollution episodes.

Aerosols are tiny particles in the air, including dust, soot and smoke, that can block sunlight. When they block sunlight, the ground cools, the air does not rise, and the atmosphere mixes less. This traps more pollution close to the surface.

The research finds that this feedback reduces the boundary layer height by up to several hundred metres, trapping pollutants and raising particulate matter concentrations by as much as 100 micrograms per cubic metre, worsening Delhi’s air quality during peak burning days. PTI SGV SLB NB