• Sat. Jun 25th, 2022

CSE releases analysis of winter air pollution trends for Delhi-NCR

ByNE India Broadcast

Mar 30, 2022

The winter season has drawn to a close, but it has left alarm bells clanging. A new analysis by Centre for Science and Environment (CSE), of winter air pollution trends in Delhi-NCR, says that while there had been a minor drop in the seasonal level compared to previous winters, the level is still extremely high, and far from meeting the safety standards. CSE researchers warn that if not acted upon immediately, this trend can worsen in the coming years negating the downward dip of the pandemic years.

This analysis of real-time data from monitoring stations in Delhi-NCR for the entire winter period (October 1, 2021-February 28, 2022) shows that despite heavy and prolonged rains in different phases this winter, long smog episodes and elevated levels have prevailed. The region recorded a few days of satisfactory air quality in January which has not happened in the previous three seasons — this was due to unprecedented heavy rainfall and the lockdown imposed on the city to control the Omicron-wave of the pandemic in January.

“Elevated pollution levels and smog episodes are an evidence of the systemic pollution that has continued in the region due to inadequate infrastructure and systems for pollution control in all sectors. This can be tamed only if round-the-year action becomes more stringent and uniform across sectors and the region. Action has to be performance based to meet the clean air standards,” says Anumita Roychowdhury, executive director, research and advocacy, CSE.  

Adds Avikal Somvanshi, programme manager, Urban Lab Analytics, CSE: “Even though there is considerable variation in seasonal averages across the region, winter pollution episodes are alarmingly high and synchronised in the region despite large distances. This is the challenge of this landlocked region. Despite being the wettest winter, the overall winter average of PM2.5 has stayed elevated and the overall contribution of the local and regional sources are higher than that from stubble-smoke.”

Data used in the analysis: The analysis is based on publicly available data from various government agencies. Most granular data (15-minute averages) has been sourced from the Central Pollution Control Board’s (CPCB) official online portal Central Control Room for Air Quality Management — All India (https://app.cpcbccr.com/ ). This has analysed data recorded by 81 air quality monitoring stations under the Continuous Ambient Air Quality Monitoring System (CAAQMS) of CPCB.

Farm stubble fire data has been sourced from System of Air Quality and Weather Forecasting and Research (SAFAR). Weather data has been sourced from the Safdarjang weather station of Indian Meteorological Department (IMD). Delhi (40), Ghaziabad (4), Noida (4), Gurugram (4), Faridabad (4), Meerut (3) and Greater Noida (2) have more than one real-time station – therefore, a city-wide average has been used for comparative analysis: it is defined as the average of all city stations that meet a minimum 75 per cent data availability criteria.   

Key highlights: Delhi

Marginal improvement in Delhi’s air quality despite the wettest winter in over a century: The city-wide winter average for Delhi stood at 172 microgramme per cubic metre (μg/m3), which is identical to the seasonal average of the winter of 2019-20 but is 9 per cent lower than the seasonal average of 2020-21 winter. The seasonal peak was about 5 per cent lower than both preceding winters.

Meteorologically, this winter was the wettest in recent years with almost two-three fold more rainfall compared to previous winters, bulk of which happened in January, making it the least polluted January since real-time air quality monitoring started in the city. But this meteorological advantage did not give much reprieve to the city as a rapid build-up in between rainy spells and formation of smog episodes during rainless periods kept overall seasonal average very high.  

Number of days with severe or worse air quality bounced back to pre-covid levels: This winter, 25 days had the city-wide average in ‘severe’ or ‘worse’ AQI category — up from 23 such days in the previous winter and at par with 25 days in the winter of 2019-20. The city also saw two days of ‘good’ air and seven days of ‘satisfactory’ air this winter, which is an improvement from the last winter season when no such low pollution days were recorded. This high variability in air quality this winter can be attributed to increased number of heavy rainfall days and colder-than-usual weather.

Intensity of winter smog dips, but duration lengthens this winter: This year’s early winter smog episode that built up around Diwali (starting on November 4, 2021), lasted 10 days — longer than the longest Diwali smog episodes recorded in previous three winters (See graph in full analysis report).Smog episodes in 2018-19, 2019-20, and 2020-21 lasted six days (starting on November 8, 2018), eight days (starting on October 28, 2019), and seven days (starting on November 4, 2020), respectively. The intensity of this year’s main smog episode was 318 ug/m3 per day, which is about 10 per cent lower than the intensity of the main smog episodes of the previous two winters. It can be argued that this marginal decline in the intensity is negated by the longer duration of the episode.

Technically, a smog episode is defined for the purpose of emergency action under the 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 does not drop below 200 ug/m3, the whole period is considered a single extended smog episode.

Similarly, the late winter smog this year started on December 21, 2021 and lasted nine days with an intensity of 340 ug/m3 per day. This was both longer and more intense compared to the previous Christmas smog which started on December 22 and lasted only three days with an intensity of 320 ug/m3. Duration-wise, the 2018 Christmas smog was the longest — lasting 17 days — in recent years. Interestingly, this is the first year when the smog intensity during Christmas smog episode is found to be higher than the intensity of its Diwali smog episode.

The days with severe air quality occurred in a cluster of days making an extended smog episode. This is different from the previous winter when they were spread across the season leading to a lesser number and duration of smog episodes. The smog pattern was similar to the one observed in the 2019-20 winter. Says Somvanshi: “This year, there were three smog episodes: the first started on November 4, 2021 and lasted 10 days, the second began on November 25 and lasted four days, and the third started on December 21 and lasted six days (see graph in full analysis report). These are more and longer compared to previous winters which had only two smog episodes lasting seven and three days.”

The 2019-20 winter had three smog episodes of eight, five and six days’ durations. The 2018-19 winter had four smog episodes of six, 17, three and five days’ durations – the last two occurring in January. Explains Somvanshi: “Relatively slow dissipation of smog episodes this year compared to previous year points towards increase in the overall pollution load in the larger air shed (all the gains of lockdowns lost) and ineffectiveness of ad-hoc pollution control efforts. Higher intensity of Christmas time smog episode also points towards increased load from local pollution.”    

Stubble burning more concentrated in time: According to SAFAR, smoke from the stubble fire in northern states started contributing to Delhi’s PM2.5 level from October 10, 2021 and ended on November 30, 2021. During these 52 days, the percentage contribution varied between 1 per cent and 48 per cent, with the latter being reported on November 7, 2021. This winter’s stubble fire season was four days shorter than the ones in the previous two winters. The number of days when percentage contribution was over 40 per cent was the same this winter as last year: two days.

But if looked at from absolute concentration terms, this year had twice the number of days when the PM2.5 load from stubble fire was high enough to plunge Delhi’s air quality into ‘very poor’ category on its own (see graph in the full analysis report). Further, these high contribution load days happened in a cluster, which indicates that the biggest bulk burning instances took place in a span of fewer days this year than in the previous years. This might be due to the extended monsoon which reduced the rain-free period before the sowing of the wheat crop.    

Winter gets smoggy even without the stubble smoke: Average concentration of stubble fire smoke in Delhi’s air during the 52 days in October-December 2021 was 28 ug/m3 per day. The rest of the PM2.5 in Delhi during those days was of non-stubble fire origin. This is consistent with the trend noted during the previous winter. Smoke from stubble fires only tips over the local-regional pollution load — which is already elevated due to inversion — to the ‘severe’ category. In fact, smog episodes during late December occur even without the influence of stubble smoke. The average daily load of PM2.5 post-stubble fire season (mid-December to end-February) when there is no influence of stubble smoke, was only 5 per cent higher than the average noted during the stubble fire season this year. As noted during previous winters as well, over 80 per cent of the daily PM2.5 level on an average is of non-stubble origin.

Variation among city’s stations remains significant, indicating dominance of local pollution sources, influence of micro climate and level of action: Thirty out of 38 stations saw an improvement in their seasonal averages over the last year. The biggest improvement was noted at Alipur and CRRI Mathura Road which registered a 17 per cent lower seasonal average this winter compared to the mean of previous three winters. The maximum increase was noted at Lodhi Road (IITM) station. Even though most stations saw improvement this winter, the pollution level remained very high. The seasonal average ranged between 252 ug/m3 at Jahangirpuri to 117 ug/m3 at Aya Nagar. This 145 ug/m3 variation within the city indicates dominance of local pollution sources and level of action in different hotspots.

Other than Jahangirpuri, stations at Anand Vihar, Wazirpur, Mundka, Rohini and Ashok Vihar also recorded seasonal averages in excess of 200 ug/m3. Lodhi Road and Rohini registered highest peak pollution days with 24-hour averages crossing 700 ug/m3. Najafgarh’s peak of 351 ug/m3 was the lowest in the city despite being almost six times the 24-hour standard (see graph in the full analysis report). Peak pollution days occured approximately around the same time across all the city stations. But there seems to be no correlation between the magnitudes of seasonal peak and seasonal average.

Wazirpur was the only recognised hotspot that registered a worsening of air: Except Wazirpur, all the locations on the Delhi-NCR pollution hotspot list saw a decline in the seasonal PM2.5 levels compared to last winter. Bahadurgarh, with a seasonal average of 131 ug/m3, continues to be the least polluted of the hotspots (see graph in the full analysis report). Jahangirpuri with a seasonal average of 252 μg/m3 was the dirtiest among the recognised hotspots. Very high levels were noted among emerging hotspots identified by CSE in the previous winter — Loni in Ghaziabad was the most polluted among the emerging hotspots with seasonal average of 247 ug/m3. Greater Noida with a seasonal average of 135 ug/m3 was the least polluted from this group.

Key highlights: National Capital Region

Ghaziabad was the most polluted among the four major satellite towns in NCR. But only Faidabad registered an increase in seasonal averages compared to last winter. Among the four big NCR cities, Ghaziabad and Noida registered a relatively greater improvement in their seasonal winter averages compared to Gurugram and Faridabad.

Pollution is rising in smaller towns of NCR, though there is a mixed trend: Ten out of 27 NCR towns show a detoriation in sesonal averages from the mean of previous three winters, even though Delhi registered an improvement. All these are smaller towns. Air quality detoriated the most in Hapur in UP, which saw a doubling of its seasonal average to 142 ug/m3 this winter. It was followed by Bhiwani and Manesar in Haryana that registered an over 30 per cent decline in seasonal air quality. Palwal and Mandikhera in Haryana registered the most improvement (exceeding 30 per cent). Half of the cities show less than 10 per cent change in their seasonal averages.

The big cities of NCR continue to be the most polluted with highest seasonal averages and peak pollution levels, but the smaller towns are not far behind. Predictably, Ghaziabad, Delhi and Faridabad were the most polluted cities in the NCR this winter. But Manesar and Baghpat with seasonal averages over 150 ug/m3 overtook Noida and Gurugram. Similarly, Hapur and Bulandshahr recorded higher seasonal averages than the industrial town of Bhiwadi. Palwal, Alwar and Mandikhera at the southern edge of NCR recorded the lowest seasonal averages.

Early winter smog synchronises across the region, but is more severe in Delhi and the big four: Normally, the smog episodes of November synchronise across the northern region, but it is more intense and lingers longer in Delhi and its immediate neighboring cities. Atmospheric changes during winter that include inversion, calm conditions, change in wind direction and a seasonal drop in ambient temperatures across North India entraps pollution. This is further tripped into the ‘severe’ category by smoke from farm fires and Diwali firecrackers during November. Air quality improves from ‘severe’ to ‘poor’ and ‘moderate’ category in cities farther from Delhi, but it remains in ‘very poor’ category in Delhi and the big four till February.

Though at a declining trend, Delhi still had the highest number of days in ‘severe’ or ‘worse’ air quality categories among the major NCR cities: Though the overall number of days in the ‘severe’ or ‘very poor’ categories reduced and stabilised during this winter, the city has still recorded a higher number of most severe days compared to other big cities in NCR during the 2021-22 winter. Delhi recorded 25 days with ‘severe’ or ‘worse’ air quality this winter. It was followed by Ghaziabad recording 16 days. Noida, Faridabad and Gurugram recorded 15 days, 13 days and 5 days of ‘severe’ or ‘worse’ category days, respectively. Despite a significant variation in the number of highly polluted days among the cities, the number of good air days are identical across the region. These two-four good air days coincide with heavy rainfall and are not the result of on-ground pollution control.

What is needed: Speed and scale of action

This final analysis of winter pollution in Delhi and NCR has shown that there is a risk of pollution bouncing back with the reopening of the economy and increased traffic intensity post-hard lockdown phases. High winter pollution only indicates the magnitude of local and regional pollution that gets easily trapped when winter conditions turn cool and calm with a deepening of inversion.

Says Roychowdhury: “This requires strong action to introduce clean energy across all sectors, transformation of urban commuting with upscaled public transport, walking and cycling infrastructure and vehicle restraint measures and long distance freight management, and complete recycling of all waste streams through a strong infrastructure for material recovery. This region now requires performance-based action to ensure clean air standards are met in a time-bound manner.”

(Report sent by Pratyusha Mukherjee)

Leave a Reply

Your email address will not be published. Required fields are marked *