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Despite low air pollution levels this winter, Delhi the most polluted of five major cities in NCR: CSE

ByNE India Broadcast

Mar 7, 2023 #CSE

“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 (CSE), while releasing here today 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 synchronised 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, Urban Lab, CSE.

The methodology

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

Key highlights

Delhi

This winter was the least polluted in last five years: The city-wide winter average for Delhi stood at 160 microgramme per cubic metre (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 per cent lower compared to the seasonal average of 2018-19 winter. Based on the subset of the 10 oldest stations, there is an improvement of almost 20 per cent. 

Peak pollution level down, but air still toxic: 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. Peak PM2.5 24-hour value, computed by averaging monitoring data from 36 CAAQMS stations located in the city, was 26 per cent lower compared to the highest recorded winter peak (546 µg/m³ in 2019-20 winter). Worst station level peak was 25 per cent lower compared to the highest recorded station level winter peak (806 µg/m³ in 2018-19 winter). 

Only one smog episode this 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. Average daily intensity of this smog stood at 287 µg/m³. This winter was first in last five years when both Diwali and late December (around Christmas) did not experience a smog episode.

Number of days with severe or severe-plus air quality lowest in last five years: This winter, 10 days had city-wide average in “severe” or worse AQI category, which is much lower compared to 24 such days in the previous winter and 33 in 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.

Variation in pollution levels among city’s stations remain significant: 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 per cent and 24 per cent lower seasonal average this winter compared to the mean of pervious three winters, respectively. Shadipur (34 per cent), NSIT Dwarka (24 per cent), National Stadium (1 per cent) and RK Puram (1 per cent) were the stations that registered an increase in seasonal PM2.5 level compared to previous winters.

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 per cent compared to the previous winter average. Noida (17 per cent), Faridabad (12 per cent) and Gurugram (6 per cent) also registered improvements in air quality, but it worsened for Greater Noida (-3 per cent).

Big cities of NCR continue to be the most polluted with highest seasonal average and peak pollution levels, but smaller towns 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 detoriation in their winter averages from the mean of previous three winters. Air quality detoriated most in Dharuhera in Haryana by 10 per cent with a winter average of 139 µg/m³. It was followed by Alwar in Rajasthan and Sonipat in Haryana that registered 8 per cent and 4 per cent declines in winter air quality respectively, compared to the average of previous three winters. Mandikhera (-70 per cent), Panipat (-60 per cent) and Palwal (-55 per cent) in Haryana registered the most improvement.

Early winter smog synchronised across the region — more severe in Delhi and the big four: Normally, the smog episodes of November are synchronised 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 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.

Though on a declining trend, Delhi still had the highest number of days in severe or worse air quality categories among the major NCR cities: Although the overall number of days with severe or very poor air quality decreased and stabilised 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.

The way forward

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. This requires region-wide implemenation of:

  • Clean fuels and emissions control systems in industry
  • Massive electrification of the vehicle fleet
  • Scaling up of integrated public transport options with vehicle restraint measures like parking restraints
  • Waste mangement based on 100 per cent segregation, material recovery and zero landfill policy
  • Clean construction and recycling of C&D waste
  • Replacement of solid fuels in households
  • Urban greening and dust control.
(A CSE Media Briefing)
Report sent by Pratyusha Mukherjee 

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