New Delhi: “This winter has been the cleanest in New Delhi-NCR since large-scale air quality monitoring started in 2018,” said Anumita Roychowdhury, executive director-research, and advocacy, Centre for Science and Environment, while releasing here CSE’s latest analysis of winter air pollution levels. A comprehensive analysis of PM2.5 trends during the entire winter season (October 2022-January 2023) in Delhi-NCR shows a “bending of the winter pollution curve and lowering of peak levels”, reports CSE.

The analysis was conducted by the Urban Lab at CSE and has revealed a continuous drop in seasonal average levels of air pollution, although elevated levels prevailed at city stations.

“This improvement is a combined effect of meteorology and emergency action based on pollution forecasting. There was heavy and extended rainfall in the early phases of the season that prevented smog episodes from building up and also lowered the seasonal average. Despite the decline, Delhi continues to remain the most polluted among the cities and towns of NCR. This downward trend will have to be sustained with much stronger action on vehicles, industry, waste burning, construction, solid fuel, and biomass burning to meet the clean air standard,” says Roychowdhury. 

“The analysis shows that there were still 10 days of severe and severe-plus air quality and one four-day-long smog episode during this winter. In the larger NCR, seasonal averages varied considerably among the cities and towns, but high pollution episodes were synchronized despite large distances. Delhi and the neighboring cities of Faridabad, Ghaziabad, Gurugram, and Noida were relatively more polluted than other NCR towns, though not significantly. This is the challenge of this landlocked region that demands even stronger action,” says Avikal Somvanshi, senior programme manager at Urban Lab, CSE.

This is an assessment of annual and seasonal trends in PM2.5 concentration for the period October 1 to January 31 for 2018, 2019, 2020, 2021, and 2022. This analysis is based on the real-time data available from current working air quality monitoring stations in Delhi-NCR.

Meteorological data for the analysis is sourced from the Palam weather station of the India Meteorological Department. Fire count data is sourced from NASA’s Fire Information for Resource Management System, specifically the Moderate Resolution Imaging Spectroradiometer and Visible Infrared Imaging Radiometer Suite. Estimates of the contribution of farm stubble fire smoke to Delhi’s air quality are sourced from the Ministry of Earth Science’s System of Air Quality and Weather Forecasting and Research.

Key Highlights

The city-wide winter average for Delhi stood at 160 microgrammes per cubic meter (µg/m³) for the October-January period, which is the lowest level recorded since wide-scale monitoring started in 2018-19. The PM2.5 level, computed by averaging monitoring data from 36 CAAQMS stations located in the city, was 17 percent lower compared to the seasonal average of the 2018-19 winter. Based on the subset of the 10 oldest stations, there is an improvement of almost 20 percent.

Like the city-wide winter average for Delhi, the winter peak pollution level was found to be the lowest recorded since wide-scale monitoring started in 2018-19. The city-wide peak this year stood at 401 µg/m³ which was recorded on November 3, 2022. The peak PM2.5 24-hour value, computed by averaging monitoring data from 36 CAAQMS stations located in the city, was 26 percent lower compared to the highest recorded winter peak (546 µg/m³ in 2019-20 winter). The worst station level peak was 25 percent lower compared to the highest recorded station level winter peak (806 µg/m³ in the 2018-19 winter).

As is the global practice, at least three continuous days of severe AQI is considered a smog episode. In previous winters, such episodes have been recorded as lasting over six-10 days. This winter, only one smog episode was recorded from January 6-9, 2023. The average daily intensity of this smog stood at 287 µg/m³. This winter was the first in the last five years when both Diwali and late December (around Christmas) did not experience a smog episode.

This winter, 10 days had a city-wide average in the “severe” or worse AQI category, which is much lower compared to 24 such days in the previous winter and 33 in the 2018-19 winter.

The city also recorded five days of good air this year which is an improvement over the previous winter which had recorded one “good” AQI day. Earlier winters did not record any good air quality days. This winter’s “good” AQI days coincided with heavy rainfall days in October.

This winter, 32 out of 36 CAAQMS stations saw improvement in their seasonal averages over the average of the last three years. The maximum improvement was noted at DTU and IHBAS which registered 41 percent and 24 percent lower seasonal averages this winter compared to the mean of the previous three winters, respectively. Shadipur (34 percent), NSIT Dwarka (24 percent), National Stadium (1 percent) and RK Puram (1 percent) were the stations that registered an increase in seasonal PM2.5 level compared to previous winters.

Despite the improvement this winter, pollution levels still remained very high across all stations. The seasonal average ranged between 115 µg/m³ at IHBAS and 211 µg/m³ at Nehru Nagar. Jahangirpuri was the second most polluted location in the city with a seasonal average of 201 µg/m³. Peak pollution ranged from 278 µg/m³ at IHBAS to 606 µg/m³ at Patparganj.

Hotspots located in North and East Delhi were the most polluted in the city. Jahangirpuri was the ‘most polluted’ official hotspot with an October-January average PM2.5 level of 201 µg/m³. Other most polluted hotspots were Anand Vihar (196 µg/m³), Wazirpur (185 µg/m³), Mundka (185µg/m³), Rohini (182 µg/m³), and Bawana (179 µg/m³). Bahadurgarh with 105 µg/m³ and Gurugram and Faridabad each with 133 µg/m³ was the least polluted among the official hotspots.

All hotspots except R K Puram have shown an improvement compared to average pollution levels recorded over the previous three winters. Greater Noida has registered the most improvement with its October-January levels this year being 18 percent lower than the average of the previous three winters. R K Puram registered a 1 percent increase for the same duration. Wazirpur (5 percent), Narela (3 percent), Mayapuri (3 percent), and Faridabad (3 percent) registered improvements, but it was less than the improvement noted in Delhi’s city-wide average.

The total count of farm stubble fires reported this year from Punjab, Haryana, and Delhi in the months of October and November stood at 55,846, according to NASA’s VIIRS satellite, and 12,158, according to its MODIS satellite. These are respectively 36 percent and 40 percent lower than the figures for October-January in 2021-22. If the FRP (fire radiative power which is the measure of the intensity of fire) is taken into account in addition to the number of fires, it becomes clear that not only were the fires lesser in the count but also lower in intensity compared to the previous two years. The total FRP this October-January has been 373 kW and 199 kW, according to VIIRS and MODIS respectively. This is 43 percent and 49 percent lower than last year’s values, respectively.

Fires have been lower this October-January both in count and intensity compared to the previous two seasons, but are marginally higher compared to the 2019-20 season. Therefore, it can be argued that the spike seen in the fires since the pandemic started has ended and the situation has reverted to a pre-pandemic scenario. This is a relatively better scenario, but we are still far from attaining our clean air objectives.

This year, smoke from farm stubble fires contributed to PM2.5 levels in Delhi for 53 days, starting October 12 and ending on December 3, 2022. This is lesser than in the previous three years when the smoke intrusion was reported on 56 days, but it is higher than the 2018-19 winter figure of 48 days. The highest contribution this year was 34 percent, reported on November 3, 2022. But given the overall low PM2.5 levels this year, 34 percent contribution accounts for much less in terms of actual PM2.5 concentration in Delhi’s air. Therefore, it is critical to look also at the absolute mass of PM2.5 that got transported to the city from the fires.

The quantity of smoke from farm stubble fires that falls over Delhi is dependent upon two major factors: quantity and intensity of farm stubble fires, and meteorological conditions conducive for transportation of the smoke to Delhi. This winter, not only the quantity and intensity of farm stubble fires have been low, but also the meteorological conditions have been less conducive for the transport of the smoke. As a result, the total smoke that fell upon Delhi in the form of PM2.5 has been considerably less. CSE researchers estimate that about 4.1 tonnes of PM2.5 fell over Delhi this winter in the form of smoke: this is 37 percent less than the 6.4 tonnes that fell last year and almost half of the 2020-21 winter figure.

In terms of absolute concentration, Delhi was the most polluted major city in NCR with a winter average of 160 µg/m3. Greater Noida with 143 µg/m3 was the next most polluted major city in NCR. Faridabad and Gurugram both registered 133 µg/m3 while Ghaziabad did marginally better with a winter average of 132 µg/m3. Noida was the least polluted major city with a winter average of 124 µg/m3.

Among the five big NCR cities, Ghaziabad registered the highest improvement in its winter PM2.5 level with a reduction of 23 percent compared to the previous winter average. Noida (17 percent), Faridabad (12 percent), and Gurugram (6 percent) also registered improvements in air quality, but it worsened for Greater Noida (-3 percent).

Big cities of NCR continue to be the most polluted with the highest seasonal average and peak pollution levels, but smaller towns are not far behind: Delhi was the most polluted city in NCR followed by Greater Noida this winter. But Dharuhera and Baghpat, much smaller towns, were next on this worst polluted list, placed above the much larger cities of Faridabad, Gurugram, and Ghaziabad. Mandikhera and Palwal were the least polluted towns in the NCR with their winter average settling below 40 µg/m³. Likewise, Delhi registered the highest peak city-wide pollution with a 24-hour average at 401 µg/m³ followed by Gurugram at 385 µg/m³ and Baghpat at 368 µg/m³. Palwal’s peak of 78 µg/m³ was the lowest in NCR.

Only four out of 25 NCR towns show a deterioration in their winter averages from the mean of the previous three winters. Air quality deteriorated most in Dharuhera in Haryana by 10 percent with a winter average of 139 µg/m³. It was followed by Alwar in Rajasthan and Sonipat in Haryana which registered 8 percent and 4 percent declines in winter air quality respectively, compared to the average of the previous three winters. Mandikhera (-70 percent), Panipat (-60 percent), and Palwal (-55 percent) in Haryana registered the most improvement.

Early winter smog synchronized across the region -- more severe in Delhi and the big four: Normally, the smog episodes of November are synchronized across the northern region. But it is more intense and lingers longer in Delhi and its immediate neighboring cities. During winter, atmospheric changes such as inversion, change in wind direction, and a seasonal drop in ambient temperatures across North India entraps pollution. Additionally, smoke from farm fires and Diwali firecrackers in November makes the situation worse. While the air quality in cities further away from Delhi improves from severe to poor and moderate categories, Delhi and the big four cities continue to have very poor air quality through the end of January.

Although the overall number of days with severe or very poor air quality decreased and stabilized this winter, Delhi still recorded more days with the most severe air quality compared to other major cities in NCR during the 2022-23 winter. Delhi had 10 days with severe or worse air quality, followed by Greater Noida with six days. Noida and Gurugram each had three days, and Faridabad and Ghaziabad each had one day of severe or worse air quality. Despite the large differences in the number of highly polluted days between the cities, the number of days with good air quality was almost the same across the region. These two-six days with good air quality coincided with heavy rainfall and were not the result of on-ground pollution control measures.

Winter pollution is the litmus test of clean air action in the region. The only way to prevent the high peaks and smog episodes during winter is to ensure sustained improvement in air quality to meet the national ambient air quality standard across the region.