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New Delhi: Though extra rainy days in the first half of October lowered air pollution in Delhi, the national capital will still need to brace for poor air quality as Diwali approaches and stubble burning picks up in Delhi, Punjab and Haryana.
As per a recent report on winter air pollution by CSE, though Diwali falls early this year – which means that weather conditions will help dilute air pollution – the likelihood of increased farm stubble fires along with pollution from Diwali celebrations could mean that a “severe smog” could begin from Diwali night. Air quality in Delhi is likely to remain in the “Very Poor” to “Poor” category, as per the government’s air quality early warning system, till October 27.
Delhi’s dipping air quality
Delhi, the National Capital Region (NCR) and surrounding areas witness high levels of air pollution during the winter months, starting October.
Fine particulate matter (PM2.5, consisting of particles less than 2.5 mm in diameter, produced from sources including fossil fuel combustion) from vehicular traffic, construction activities and emissions from thermal power plants are some of the causes for the high pollution levels in the city.
Local weather conditions can also play a role in air quality levels. The lack of winds, for example, can concentrate pollutants in the area and spike air pollution levels.
However, the burning of crop residue in agricultural fields is the main cause of poor air quality in Delhi and the NCR during winter. This happens when farmers set crop stubble on fire to prepare their fields for the next growing season. India measures its air quality for areas including cities through the Air Quality Index (AQI), which calculates levels of various pollutants and the resulting quality of air using data from air quality monitoring stations in the area.
According to the Central Pollution Control Board (CPCB), Delhi’s AQI (averaged across 35 monitoring stations for 24 hours) on October 21 at 4 p.m. was 262. According to the Ministry of Earth Science’s Air Quality Early Warning System, the Air Quality and Weather Bulletin for Delhi NCR as on October 21 predicted that the overall air quality over Delhi is “likely to remain” in the ‘Poor’ category on the same day.
The forecast by the early warning system also added that Delhi’s AQI will likely remain in the ‘Very Poor’ to ‘Poor’ category for the next six days. ‘Poor’ air quality can cause breathing discomfort to people under prolonged exposure, and when it dips to ‘Very Poor’, this can cause respiratory illnesses.
Rains helped, as will an early Diwali
As per a report published by the Centre for Science and Environment on October 19, rains in the first two weeks of October “kept air quality in check” in Delhi. Rains can bring down the air pollution levels as raindrops wash out particles and atmospheric gases suspended in the air. However, air quality is starting to deteriorate, it noted. This is because stubble burning has picked up in Delhi, Haryana and Punjab, though it is not in full swing yet. Emissions from firecrackers during Diwali celebrations will “accelerate this deterioration”, the report said.
Moreover, because Diwali falls early this year (October 24), the warmer and windier conditions will help dilute the pollution caused due to celebrations on the night of the festival, the report added. But despite this, Diwali night alone could witness an addition of 300-600 μg/m3 of PM2.5 to Delhi’s air, based on previous years’ data.
This, along with the strengthening of stubble burning which will continue after Diwali, may set the stage for a “severe smog episode” starting Diwali night, the report said.
The report assessed annual and seasonal trends in PM2.5 concentrations between January 1, 2015 and October 17, 2022 using several sources such as data from air quality monitoring stations, counts of stubble fires, etc. The assessment also found that there has been a 20% improvement in seasonal air quality in recent winters when compared to winters between 2015 and 2018. However, this improvement has stagnated since the pandemic.
Between 2015 and 2022, rains and smoke from stubble fires played a major role in air quality in Delhi, the former offering temporary relief from higher pollution, and the latter worsening air quality levels.
The report also found that pollution levels on Diwali night (from 8 pm to 8 am) remained consistently high during these years. Hourly concentrations of PM2.5 went beyond 1,000 μg/m3. Smog days and intensities also “remain worrisome”.
Last year saw 20 smog days in total, when compared to 14 the year before.
Stage-II measures to tackle “Very Poor” air quality
When air quality dips to ‘Poor’ and lower levels, the government puts the Graded Response Action Plan (GRAP, set up under the Commission for Air Quality Management in NCR and Adjoining Areas), a set of emergency measures for varying levels of low air quality, in place. This year, for instance, the government invoked Stage I of GRAP on October 5 when air quality in the national capital deteriorated to ‘Poor’.
As per a government press release, the Air Quality Early Warning System predicted that Delhi’s AQI will cross 300 on October 22, moving to the “Very Poor” category. This would necessitate implementing Stage II of the GRAP. In light of this, the Sub-Committee for the operationalisation of GRAP held an emergency meeting on October 19 and decided to invoke Stage II on the same day. Measures under this stage include stopping the use of diesel generators except for very specific essential and emergency services, not permitting the burning of coal or firewood in hotels, restaurants and open eateries, and so on.