Delhi’s seasonal winter PM2.5 average had improved during the pandemic, but it stagnated post-pandemic
Action this winter will determine if the curve will bend or rise further
See detailed note with analysis Read more
New Delhi, October 20, 2022: As Delhi and the National Capital Region (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 buthad stagnated post-pandemic -- will furtherbend or increase. This winter season is also starting from a much cleaner benchmark due to rains in September and October.
Centre for Science and Environment’s (CSE) 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.”
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.
“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 candelay and lead to concentrated burning latercompounding 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 1 January 2015 to 17 October 2022 (winter is defined as from October 1 to February 28). This captures seven successive winter seasons and pre-winter trends in Delhi and the National Capital Region. 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.
This analysis covers 81 continuous ambient air quality monitoring stations (CAAQMS) spread across cities of Delhi-NCR. Meteorological data for the analysis is sourced from the Palam weather station of India Meteorological Department (IMD). Fire count data is sourced from NASA’s Fire Information for Resource Management System, specifically Moderate Resolution Imaging Spectroradiometer (MODIS) and Visible Infrared Imaging Radiometer Suite (VIIRS) product is used. Estimate of contribution of farm stubble fire smoke to Delhi’s air quality is sourced from Ministry of Earth Science’s System of Air Quality and Weather Forecasting and Research (SAFAR).
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 per cent 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 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 forthe winter (post-pandemic) shows about 20 per cent 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 capon 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.
It must also be noted that the worst station for peak pollution has changedseven times in last seven winters. Shadipur, DTU, CRRI Mathura Road, JLN Stadium, Alipur, ITO and Rohini have occupied the worst peak pollution title in the last seven winters. These are spread across the city with no clear pattern. This indicates that the winter pollution is regional in nature and short-term peak build-up can happen anywhere based on local meteorology and pollution sources.
Seasonal PM2.5 average for 2021-22winter was 10-30 per cent lower compared to 2020-21 winter for most major NCR cities - but Ghaziabad and Faridabad fared worse among these cities: Winter of 2021-22 was relatively less polluted compared to winter of 2020-21 for most NCR cities. Ghaziabad registered a 30 per cent improvement that was highest among major cities, but its PM2.5 level was still about 2.5-times the 24-hr standard. Greater Noida (28 per cent), Noida (23 per cent) and Faridabad (16 per cent) also registered improvement in excess of Delhi that registered a 12 per cent improvement. Gurugram with 11 per cent improvement was the worst performer among the core NCR cities. In absolute concentration terms, Faridabad with seasonal average of 159 µg/m3 was the most polluted city of NCR last winter.
Across the larger NCR, Muzaffar nagar was worst performer as it registered a 1 per cent 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-hr 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 lowersthe 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 (8pm to 8am) 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.
2022 monsoon was the second cleanest in last eight years: The seasonal average for the monsoon (July, August and September) this year stood at 37 µg/m3 which is only marginally higher than lowest monsoon average of 36 µg/m3 that was recorded during the 2020 monsoon. The ultra-low pollution level recorded during the 2020 monsoon were preceded by a cleanest ever summer (March-May) due to extraordinary conditions created because of lockdowns. But this monsoon has been preceded by one of the most polluted summers –therefore, it is important to understand what aided in cleaning up the Delhi air. Looking at the rainfall data it becomes evident that distribution of rainfall has a relatively higher impact on seasonal air quality than the absolute quantity of rainfall. This monsoon, there have been 45 rainy days compared to just 39 in the previous monsoon. These six extra rainy days helped keep the seasonal average low despite the fact that the total rainfall this monsoon was just one-third of the previous monsoon. These additional rainy days also pushed the regular start of bad air quality days further down the month of October.
Rains kept air quality in check during the first two weeks of October: Delhi received an unprecedented 115 mm of rainfall in the first two weeks of October this year -- this translated intothe cleanest start to winter since wide scale monitoring started in 2018. The PM2.5 average for the first two weeks of October stood at 43 µg/m3 which is less than half of the level recorded in 2020 for the same period. This October, so far,there have been five days of “good” AQI (PM2.5 sub-category), which is the most recorded in the last eight winter seasons. All these “good” AQI days fell on the rainy days. Last year, two “good” AQI days were recorded for the entire winter season, while the previous winters had no “good” AQI days.
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:
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