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REPORT
Bending Delhi’s Air Pollution Curve
Learnings from 2020 to Improve 2021
10 June, 2021
L. S. Kurinji, Adeel Khan and Tanushree Ganguly

Suggested citation: Kurinji, L. S, Adeel Khan, and Tanushree Ganguly. 2021. Bending Delhi’s Pollution Curve: Learnings from 2020 to Improve 2021. New Delhi: Council on Energy, Environment and Water.

Overview

The study intends to support the Delhi government, the Central Pollution Control Board (CPCB), and the Delhi Pollution Control Committee (DPCC) in identifying priority areas of interventions needed in controlling air pollution in Delhi during the winter season of 2021. It establishes the primary drivers of Delhi's winter air pollution during the different phases of the season. It considers meteorological parameters, source activity levels, and its contributions to investigate how winter 2020 was, if at all, different in the pandemic circumstances compared to the previous years.

Key Highlights

  • Delhi residents were exposed to air that does not meet the National Ambient Air Quality Standards (60 µg/m3) for more than half of 2020 despite low economic activity levels for close to eight months (March to November) due to the pandemic-induced lockdown.
  • Delhi’s air quality in winter 2020 was worse than winter 2019 with 92 severe and very poor air quality days in the winter of 2020 compared to 80 such days in 2019.
  • Relative contribution from farm fires was the highest (~30 per cent) between 15 October and 15 November 2020. In the following months, the contribution from household emissions (including domestic cooking, space heating, water heating, and lighting) primarily drove poor air quality in Delhi.
     

air pollution in delhi during winter season

Source: Author’s analysis
  • Calmer winds in October and November amplified the impact of farm fires on Delhi’s air quality. The stubble burning phase (15 October to 15 November) in 2020 experienced 172 hours (70 per cent higher) of calm and light winds (<5 km/h) compared to 101 hours in 2019.
  • Activity levels were low at the start of the winter. But most activities, including vehicular traffic and power generation, bounced back to the previous year’s levels (proxied by indicators such as congestion and electricity generation levels) as the season progressed.
  • Adverse meteorological conditions in Delhi intensified the impact of local and regional emissions on Delhi’s air quality. While meteorological conditions cannot be controlled, sustained air quality gains can be realised only by steeper emission cuts across sectors.

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L. S. Kurinji
Programme Associate
Calmer winds in October and November amplified the impact of farm fires on Delhi’s air quality. The stubble burning phase (15 October to 15 November) in 2020 experienced 172 hours (70 per cent higher) of calm and light winds (<5 km/h) compared to 101 hours in 2019.

Executive Summary

Delhi is among the most polluted cities in the world (IQ Air 2021). In 2019 alone, air pollution caused over 17,000 premature deaths and an economic loss of 1,207 million USD in the national capital (Pandey et al. 2021). With regards to air quality, 2020 was an aberration. The pandemic-induced lockdown measures provided temporary respite from the year-round poor air quality. 

Despite the lockdown, Delhi’s annual average PM2.5 in 2020 was more than 2-times its permissible limit

Barring a few days in April and May, Delhi experienced National Ambient Air Quality Standard (NAAQS)1 compliant air quality on most days during the lockdown. Yet, the annual average PM2.5 concentration in 2020 was 93 µg/m3, which is more than twice the permissible limit for PM2.5 in India. Despite low activity levels for close to eight months (March to November) in 2020, Delhi residents were exposed to NAAQS non-compliant air for more than half of the year (Figure ES1).

measures to control winter air pollution in delhi

Winters saw poor quality despite proactive measures by the government

While the NAAQS non-compliant air quality in Delhi is not a new phenomenon, the winter of 2020 witnessed proactive measures from the State Government in the wake of COVID and evidence pointing at the association between high air pollution and COVID mortality (Petroni et al. 2020; Cole, Ozgen, and Strobl 2020; Wu et al. 2020). This includes the Yuddh Pradushan Ke Virudh (war against pollution) campaign and a seven-point action plan to combat air pollution in Delhi which listed measures ranging from combating dust and mitigating hotspots to a mobile application called Green Delhi for complaints and a ‘war room’ for monitoring air pollution control activities (PTI 2020a). Similar to 2019, the Graded Response Action Plan (GRAP), also came into force on 15th October 2020 and the Environmental Pollution Control Authority (EPCA)2  oversaw its implementation until the announcement of its dissolution on 28th October 2020 (Koshy 2020; EPCA 2020). However, despite these measures, the PM2.5 levels remained almost three times higher than the NAAQS on an average between October 2020 and January 2021. We also observe that PM2.5 levels in winter 2020 were higher than those in 2019. To explain this end, we analyse meteorological parameters, source activity levels, and contributions to establish primary drivers of pollution during different phases of the winter season. Through this brief, we intend to help the Delhi government, the Central Pollution Control Board (CPCB) and the Delhi Pollution Control Committee (DPCC) to identify priority areas of intervention for the year 2021. We summarise key highlights as follows

Air quality in winter 2020 was worse than winter 2019


Delhi observed 92 severe and very poor air quality days in the winter of 2020 compared to 80 such days in 2019. Compared to an average PM2.5 concentration of 161 μg/m3  in 2019, between October and November 2020, this value was 172 μg/m3. It further shot up to an average level of 192 μg/m3  in the period between December 2020 to January 2021 compared to 178 μg/m3 during the same period previous year.

Contributions from stubble burning and household emissions from cooking and space heating were significant fractions of the pollution pie

Modelled source contribution estimates of particulate matter (PM2.5) by UrbanEmissions suggest that relative contribution from farm fires was the highest (~30 per cent) in the period between 15 October and 15 November 2020 (Figure ES2). We find that compared to the stubble burning period in 2019, a longer harvesting season in 2020 led to a significant increase in the number of fires. In the following months, contribution from household emissions (including domestic cooking, space heating, water heating, and lighting) primarily drove poor air quality in Delhi. It is worth highlighting that these values are modelled estimates and are subject to the sector-specific assumptions used in the model.

preventive measures for delhi's air pollution

Calmer winds in October and November amplified the impact of farm fires on Delhi’s air quality

The stubble burning phase (15 October to 15 November) in 2020 experienced 172 hours (70 per cent higher) of calm and light winds (<5 km/h) compared to 101 hours in 2019. Winds predominantly from the north-west direction facilitated the transport of smoke emanating from farm fires and calm winds in Delhi further intensified its adverse impact on air quality. Interestingly, for brief periods in the season, even when high fire counts were reported in Punjab and Haryana, Delhi’s air quality was not affected due to favourable meteorological conditions (Easterly and southerly winds) (Figure ES3). Unfavourable meteorological conditions include low wind speeds and shallow mixing height height3 .

delhi winter pollution control

Lowered activity levels at the start of winter due to lockdown bounced back to the previous year’s levels as the winter progressed

While Delhi’s average PM2.5 concentration during the stubble burning period (October’20 and November’20) was 172 µg/m3, it increased to 192 µg/m3 during peak winter (December’20 and January’21). The higher PM2.5 levels in December 2020 and January 2021 were primarily caused by locally emitted pollutants and added burden of household emissions from space heating. Activity levels were low at the start of the season, but most activities, including vehicular traffic and power generation, bounced back to the previous year’s levels (proxied by indicators such as congestion and electricity generation levels in Figures ES4 and ES5) as the season progressed. 

delhi air pollution control

Delhi needs a dedicated air quality forecasting cell to facilitate roll out of preventive measures


We attribute the brief periods of moderate air quality during winter 2020 largely to favourable meteorological conditions. It is evident that adverse meteorological conditions in Delhi intensified the impact of local and regional emissions on Delhi’s air quality. While meteorological conditions cannot be controlled, sustained air quality gains can be realised only by steeper emission cuts across sectors. Delhi has in place a publicly available air quality forecast system provided by UrbanEmissions for over five years. The Indian Institute of Tropical Meteorology (IITM), under the aegis of Ministry of Earth Sciences (MoES), has also built an official air quality warning system for Delhi (PIB 2018). However, none of these forecasts were actively used to take pre-emptive measures to reduce emission loads from anthropogenic activities. Some countries roll out emergency measures in response to air quality (AQ) forecasts and not after air quality actually dips to dangerous levels. For instance, Beijing’s Ministry of Ecology and Environment issues a red alert if the daily mean citywide air quality index (AQI) is forecasted to be greater than 200 for four days (96 hours) or more; greater than 300 for two days (48 hours) or more; or greater than 500. In contrast, the Delhi government issues orders to execute emergency measures under GRAP ex-post, that is, after air quality concentrations reach a certain threatening level. Responsive measures cannot prevent the occurrence of high pollution episodes. Further, adding relative source contributions to air quality forecasts, similar to the way UrbanEmissions issues forecasts, can help identify the primary contributors during a particular episode. Integrating such forecasts with a decision support system would enable the local regulatory agencies to implement on-demand emission control interventions targeting prominent sources during forecasted high-pollution episodes. The Graded Response Action Plan (GRAP) presents the state government with an opportunity to constitute an air quality forecasting cell that can advise the government to take necessary measures to prevent severe air quality episodes in the capital city. We recommend that going forward, the Delhi government, the CPCB, and the DPCC use the air quality forecasts not only to issue public health warnings but also for taking pre-emptive actions in the national capital. We must move from a system that enforces the Graded Response Action Plan as an ex-post measure to one that prevents the occurrence of high pollution episodes through pre-emptive emission control measures.

 

How can Delhi’s air pollution be controlled?

Delhi needs a dedicated air quality forecasting cell to facilitate the rollout of preventive measures

Some cities, such as Beijing, roll out emergency measures in response to air quality (AQ) forecasts and not after air quality dips to dangerous levels. In contrast, the Delhi government orders execute emergency measures under the Graded Response Action Plan (GRAP) ex-post after air quality concentrations reach a certain threatening level. However, such responsive measures cannot prevent the occurrence of high pollution episodes. Integrate air quality forecasts with a decision support system to enable the local regulatory agencies to implement on-demand emission control interventions targeting prominent sources during forecasted high-pollution episodes. The Delhi government, the CPCB and the DPCC should use the air quality forecasts developed by the Indian Institute of Tropical Meteorology (IITM) to issue public health warnings and take pre-emptive actions in the national capital. Move from a system that enforces the GRAP as an ex-post measure to one that prevents the occurrence of high pollution episodes through pre-emptive emission control measures.
Conclusion

“I see skies so blue and clouds so white … What a wonderful world,” wrote Bob Thiele and George David Weiss in 1967. I t took a pandemic and complete shutdown of activities for blue skies and white clouds to appear in Delhi. This respite from year-round air pollution was short-lived and the gains from cessation of activities were lost with the unlock of economic activities and the arrival of winter in Delhi. Despite the reduced activity levels for close to eight months (March to November) in 2020, Delhi residents were exposed to NAAQS non-compliant air for more than half of the year. Our analysis compared the anthropogenic activity levels and meteorological conditions in 2020 with those in 2019. We also explain how these factors influenced air quality in the winter of 2020. We find that air quality in the winter of 2020 was worse than in the winter of 2019. Lower vehicular congestion and power generation levels in October and November 2020 are indicative of reduced emissions from these two activities. A relatively longer stubble burning period, colder and drier winter conditions, and calmer winds in October and November 2020 were primarily responsible for the worsening Delhi’s air quality that year. As the winter season progressed, most anthropogenic activities such as power generation and vehicular levels bounced back to previous year’s levels. Household heating and cooking contributed to a significant share (40 per cent) to the pollution burden in December 2020 and January 2021. We stress that the interplay of meteorological conditions on Delhi’s air quality cannot be discounted, but there is need for steeper cuts in emissions across sectors. The GRAP presents the state government with an opportunity to constitute an air quality forecasting cell that can advise the government to take necessary measures to prevent severe air quality episodes in the capital city. We recommend that in addition to supporting source identification studies, the government should also encourage air quality modelling and forecasting efforts. Augmenting the existing monitoring infrastructure would help air quality modellers validate their forecasts. The state government and the city administration could also work collaboratively with the modellers in developing necessary databases to track emissions from local anthropogenic sources. 

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L. S. Kurinji
Programme Associate

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