It’s alert time for Delhi’s wintry ‘darkness at noon’

Air quality improved during peak pandemic, has been stagnant: action now will determine future

GN Bureau | October 20, 2022


#NCR   #Delhi   #air pollution   #pollution   #Environment  
A typical day in winter in Delhi in recent years (File photo: Arun Kumar/GN)
A typical day in winter in Delhi in recent years (File photo: Arun Kumar/GN)

*   Delhi’s seasonal PM2.5 average during and after the pandemic shows about 20% improvement compared to the 2015-18 winters. But the progress has stagnated.

*    In National Capital Region (NCR) cities, seasonal PM2.5 average for 2021-22 winter was 10-30% lower than 2020-21 winter; Ghaziabad and Faridabad have fared worse among the major NCR cities.

*    The 2018-19 winter had recorded the highest number of smog days (31).

*    Farm stubble fires of Punjab-Haryana-Delhi have increased in numbers and intensity.

*    Diwali night pollution has continued to remain high till last year.

*    There is need for strong preemptive and preventive action to control pollution from all key sources with zero tolerance across Delhi-NCR.

These are the highlights of the alert report issued by the Centre for Science and Environment (CSE) on Thursday.

As Delhi and the NCR brace for the upcoming winter, it remains to be seen if the seasonal average of PM2.5 during winter – that had improved during the pandemic but had stagnated post-pandemic – will further bend or increase. This winter season is also starting from a much cleaner benchmark due to rains in September and October.

The CSE’s Urban Lab has released its winter pollution assessment. The objective, says Anumita Roychowdhury, executive director, research and advocacy, CSE, has been “to understand the trend and the starting line of the onset of the winter pollution season or pre-winter levels in this region. This would also capture the longer term context of seasonal variation and annual trends in particulate pollution.”

See detailed note with analysis: https://www.cseindia.org/Start-of-Winter2022-note.pdf

This is the first analysis of the third edition of Urban Lab’s Air Quality Tracker Initiative which was started in 2020-21 winter to study the impact of pandemic lockdown on the air quality of Delhi-NCR.

“The intensity of winter pollution and severity of smog episodes will depend on the effectiveness of the long term multi-sector action so far in the entire region of Delhi and NCR and also on the enforceability of the short term emergency action. Only the effectiveness of the air pollution control measures targeting all key sources will determine if the winter pollution trend that had stabilised post pandemic, will continue to hold and improve or worsen further,” says Roychowdhury in the release.

“The onset of the winter has been much cleaner this year due to the rains. But the intensity of the early winter pollution will depend a lot on the trend in the crop fires and also the impact of Diwali. Though Diwali is happening during the warmer part of the early winter, prolonged rains can delay and lead to concentrated burning later compounding the problem,” says Avikal Somvanshi, analytic expert at the Urban Lab. 

This is an assessment of annual and seasonal trends in PM2.5 concentration for the period January 1, 2015 to October 17, 2022 (winter is defined as from October 1 to February 28). This captures seven successive winter seasons and pre-winter trends in Delhi/NCR. This analysis is based on the real-time data available from the current working air quality monitoring stations in Delhi-NCR. A huge volume of data points have been cleaned and data gaps have been addressed based on USEPA method for this analysis.

Key findings

This winter has started on the cleanest note with five “good” AQI days (for PM2.5) in the first two weeks of October. This happened due to an extended rainfall period but effects of it have started to wane as PM2.5 levels have risen above 90 µg/m3 (“poor” AQI breakpoint) on October 16. This pollution level is still low compared to previous years but it is expected to rise quickly. This rise is being driven by smoke from the farm stubble fires starting to enter the region.

As per SAFAR, this smoke contributed about 3% to Delhi’s PM2.5 level on 17th October. This is happening now because burning activities have picked up in Punjab-Haryana-Delhi. The total radiative fire power of these fires in Punjab-Haryana-Delhi breeched 2,000 Watt on 16th October. This is less than half of the value recorded in 2020 and 2021 for the same period, implying massive burning is in store in coming few days. Based on previous years’ observation it can be said that situation can worsen if business as usual scenario continues.

Seasonal PM2.5 average for the winter (post-pandemic) shows about 20% improvement compared to the winters of 2015-18; but the progress has stagnated: Overall, long term data shows that improvement made in reducing pollution levels during the winter season has stagnated in last three years. Smog episodes are again starting to get longer and pose dire threat to public health not just in Delhi but whole of NCR.  Delhi’s seasonal air quality for winter (1 Oct to 28 Feb) used hover around 180-190 µg/m3 before pandemic and for last three winters it has come down to 150-160 µg/m3. Despite the improvement the seasonal average is still over 150 per cent above the 24-hr standard and almost four times the annual standard.

Peak pollution shows similar trend as seasonal average. Peak pollution (worst 24-hr average) used to cross 800 µg/m3 at individual stations pre-pandemic, it has been hovering in 700-800 µg/m3 range during last three winters. These peak pollution numbers should be taken with caution as CPCB introduced at 1,000 µg/m3 cap on reported real-time data in 2016-17, which has greatly compromised the assessment of peak pollution level. Actual peak levels must be higher than what CPCB data shows.

Across the larger NCR, Muzaffarnagar was worst performer as it registered a 1% increase in winter level. Bulandshahr with 28 per cent improvement was the best performer among major non-core NCR cities. Baghpat with seasonal average of 142 µg/m3 was the most polluted city outside the core-NCR. Alwar with winter average of 50 µg/m3 was the only major city in NCR that registered a seasonal level lower than the 24-hour standard.

Intensity and duration of smog episodes remain worrisome:
A smog episode is defined for the purpose of emergency action under Delhi’s Graded Response Action Plan when the levels of PM2.5 remain in “severe” category for three consecutive days. In this study, if two consecutive smog episodes are separated by only one day and the PM2.5 level of that day doesn’t drop below 200 µg/m3 then the whole period is considered a single extended smog episode. Last winter season, there were three distinct smog episodes counting 20 smog days (see Table in full report). This was more than the previous two winters. 2020-21 winter had 14 smog days while 2019-20 winter had 19. Most smog days were observed in 2018-19 winter when four smog episodes were recorded with total of 31 smog days. Average intensity of smog episode last winter was 306 µg/m3 which was lower than that of previous two episodes, but this marginally lower intensity is negated by the longer duration of the smog episodes.

It must also be noted that winters with relatively lower seasonal averages have longer and more smog episodes. This requires deeper investigation.

Impact of rain and farm stubble fire smoke on the air quality is highly pronounced: 
Each year, the air in October and November becomes unbreathable due to the clustering of pollution-causing and compounding events. The festive season leads to increases in local pollution due to traffic chaos and firecrackers, which is compounded by the cooling of the weather that lowers the mixing height and sets in inversion. Burning of crop waste in Punjab and Haryana further adds to the pollution load, which is compounded by the retreating monsoons, which transport the smoke down the Gangetic Plains. Only sobering element during these two months is rain, which can wash down the pollution if the downpour is strong and prolonged – but it is only a temporary relief. This relationship is evident from the data.

Farm stubble fires of Punjab-Haryana-Delhi are increasing both in numbers and intensity:
Last year registered highest instances of farm stubble fire in the last seven years -- 2021 October-November saw a 10 per cent jump in observed fire count by MODIS and 5 per cent increase by VIIRS compared to 2020 October-November. Similarly, the total fire radiative power from these fires were 13 per cent and 7 per cent higher compared to the 2020 fires as observed by MODIS and VIIRS respectively. In fact, there is a consistent increase in fire instances and intensity since 2019. It remains to be seen what will happen this year.

Diwali night pollution continued to remain high in previous years:
PM2.5 concentration on Diwali night (8 pm to 8 am) last year stood at 747 µg/m3, 22 per cent higher than that in the 2020 Diwali night. The levels on 2021 Diwali night were 4.5 times the average night-time levels recorded in the week preceding Diwali. It is noted that hourly concentrations can go beyond 1,000 µg/m3. In the 2021 Diwali, 26 of 38 operational monitoring stations hit the 1,000 µg/m3 mark. In 2020, 23 out of 38 stations had hit the 1,000 µg/m3 mark, while in 2019 the number stood at 22 stations.

Air quality is starting to deteriorate:
Relief given by extended rainfall period has come to an end as PM2.5 levels have risen above 100 µg/m3 on October 16. This is still low compared to previous years but it is expected to rise quickly. Smoke from farm stubble fires that have started is contributing to the trend. As per SAFAR, this smoke contributed about 3 per cent to Delhi’s PM2.5 level on October 17. This is relatively low compared to contribution in previous years for this time of the year. This is happening now because burning activities have picked up in Punjab-Haryana-Delhi. The total radiative fire power of these fires in Punjab-Haryana-Delhi breeched 2,000 Watt on October 16, which is less than half of the value recorded in 2020 and 2021 for same period. Based on previous years’ observations, it can be said that the situation can worsen if a business-as-usual scenario continues.

Prevent Diwali trigger of a deadly smog episode:
This year Diwali is falling relatively early in the season which means the warmer and windier conditions will help dilute the pollution that is staple of Diwali night celebrations. Unlike previous two years, the smoke from the farm stubble fires has not overwhelmed the air quality of the region yet and rains in early October have also kept the air relatively clean so far.

Previous years’ data shows that Diwali night can add 300-600 µg/m3 of PM2.5 to Delhi’s air if business-as-usual scenario continues. It remains to be seen if farm stubble fires will increase during and post-Diwali. Delayed start of the burning season in the past has resulted in concentration of burning activities, which can intensify the smoke-fall in the region.

The next steps

Says Roychowdhury: “This early winter alert is a wake-up call for more stringent pre-emptive and preventive measures to avert the smog episodes that cause excessive exposure and health risk during winter. The enforcement of the GRAP needs to be equally stringent with zero tolerance across Delhi and NCR. This requires preparedness in all concerned departments to ensure:

*    All waste streams are collected, segregated and transported to prevent accumulation of waste in the open. Ongoing legacy waste management needs additional measures to ensure that dumpsites do not catch fire.

*    Access to clean fuels in industry needs to be scaled up and units without air pollution control equipment or consent to operate are not allowed to function.

*   Intensify public transport strategies and enforce parking controls and pricing as a demand management measure to reduce vehicle usage. Incentivise use of electric vehicles.

*    Identify key commercial areas in Delhi and NCR towns that can be pedestrianized and be declared low emission zones.  

*    Dust control in construction sites and management of construction and demolition waste should be implemented with zero tolerance.

*    Disclose information on truck movement based on the RFID data set to inform and control the intensity of the heavy duty traffic in the city.

*    Identify all unpaved roads and dust hotspots for immediate action and paving.

*   Stringent measures are needed to control fugitive dust and industrial waste burning and the mechanism need to be put in place for all industrial areas.

*    Step up action to provide access to LPG and electricity to all eateries and households to prevent burning of solid fuels.

*    Ensure access to reliable electricity supply in all residential and commercial/industrial areas to minimise use of diesel generator sets. Make DISCOMS liable and accountable for the outages in Delhi-NCR.

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