Trends of Delhi’s air quality and stubble burning during the October-November period

Manoj Kumar and Sunil Dahiya

Air pollution is a global known hazard to public health and the economy. Source emissions and meteorology govern the prevalent pollution at any location, and when the meteorological conditions change, they lead to higher dispersion or buildup of pollution levels in any geography. Winter months, due to lower temperatures, slow wind speed, insolation, and resultant inversion layer, are known to build up or trap pollutants leading to high pollution levels. India, and particularly northern India, has severe pollution during the winter. Most cities in northern India, including Amritsar, Chandigarh, Delhi, Lucknow, Patna and Kolkata, show hazardous pollution levels starting in October when they exceed the National Ambient Air Quality Standards (NAAQS) prescribed by the Central Pollution Control Board (CPCB).

In the current piece, we attempt to track the particulate matter concentrations in Delhi and trends in fire incidents in agricultural land across Punjab and Haryana to investigate how they correlate. While we look at understanding the trends and correlations, we have also provided a commentary on what can be expected in terms of air pollution levels over the next three to four weeks based on past trends and data.

With the rains between 5 and 11 October giving Delhiites a brief respite from air pollution, the city’s ambient air quality has deteriorated significantly since then and will continue to do so with winter fast approaching. 

The causes behind Delhi’s unbreathable air include a lack of emission control technologies in major sources of pollution, vehicular emissions, and episodic events of stubble burning, all of which are then governed by the region’s weather, making Delhi’s air extremely hazardous.

Figure 1: PM2.5 and PM10 concentrations (µg/m3) in Delhi over the past 5 years (weekly moving average)

Apart from the monsoon months (July-September), Delhi’s ambient air pollution is significantly higher than the annual (40 µg/m3) and daily (60 µg/m3) PM2.5 standards set by the Central Pollution Control Board (CPCB) in India.

Figure 2: Days in 2022 with PM2.5 levels above NAAQS and WHO guideline concentration in Delhi (µg/m3)

The data also suggests that the air quality deteriorates between the last week of October to mid-November. The worsening air quality can be attributed to stubble burning for 15-20 days (between the last week of October and mid-November) and firecrackers around the Diwali festival celebrations in addition to the existing sources. The PM2.5 concentration during this period reached ~500 µg/m3 in the past few years, while PM10 was more than 700 µg/m3 on a 24-hour basis.

Figure 3: PM2.5 and PM10 concentrations (µg/m3) in Delhi over the past 5 years (October- November)

Going by the trends (as shown in Figure 4),  intensive stubble burning in farms is expected to increase in the following weeks, further increasing PM2.5 levels, which is around 110 µg/m3 already. Figure 3 above shows that the three to four week window from the end of October to mid-November records the highest pollution concentrations during the October and November period.

Figure 4: Daily fire counts during the paddy harvest season in Haryana, Punjab and Delhi since 2017

Figure 5: Daily fire counts in Haryana, Punjab and Delhi and PM2.5 concentrations in Delhi (µg/m3)

The upwind air parcels containing emissions from industrial and power station operations, stubble burning and other pollution sources arriving in Delhi add to the city’s pollution levels and contribute to the prevailing pollution levels. The back trajectory analysis (Figure 6) of the air parcels arriving in Delhi reveals that the biomass burning/farm fires contribute to Delhi’s deteriorating air quality during April-May (wheat harvest) and October-November (paddy harvest). The latter is more severe because of the higher number of fire counts, with stable meteorological conditions making it worse. 

Figure 6: Back trajectory analysis of the number of fires affecting Delhi’s air quality (2015-2021)

The same or even higher pollution levels are expected across other cities and rural areas in Delhi’s Airshed, which includes Gurgaon, Ghaziabad, Noida, Faridabad, Panipat, Ambala, Amritsar, Jalandhar, etc. So the approach to reduce air pollution levels will need to be comprehensive and systematic in order to have significant pollution reductions across the region and not just centred around the impact on Delhi and its pollution.

Enabled by financial support and technological interventions from the CPCB and state governments, the number of fire incidents have reduced slightly. However, stubble burning remains a significant contributor to Delhi’s unbreathable air in October and November. 

Despite a ban on biomass burning, the incidents of biomass burning across Haryana and Punjab are expected to pick up, causing further deterioration of air quality in Delhi-NCR. The predominant wind direction during the upcoming weeks has historically been from the west and northwest, which brings pollution from biomass burning and emissions from industrial and fossil fuel based-power stations to both upwind states. 

With Diwali coinciding with the start of the peak intensive biomass burning, the air quality is expected to be worse than the existing 110 µg/m3,  which is twice the NAAQS and ten times worse than the WHO guidelines for PM2.5.

State agencies should take immediate precautionary measures, including assisting farmers in better managing the straw generated from the year’s harvest. This needs to be on a war-footing basis as farmers need to clear the straw in the small window between harvesting padding and sowing wheat. Lack of government support towards small and marginalised farmers leaves them with no choice but to burn their stubble. 

To manage this annual crisis better, government agencies must engage with farmers and advocate alternatives to stubble burning. Some interventions include promoting polyculture in farming, better minimum support price (MSP) for other crops, changing paddy sowing patterns and in-situ and ex-situ stubble management. These interventions also generate similar or even better profits for the farmer while significantly reducing stubble burning. Farmers should be given multiple options to reduce stubble burning as one solution can’t fit all, and different solutions work at different gradients in different geographic, socio-cultural and economic regions.