A new pre-Diwali and pre-winter analysis of air pollution in Delhi by Centre for Science and Environment (CSE) has found that despite a slowdown in farm fires, the air quality in the capital has been going for bad to worse – and the reason is high contribution of local air pollution sources such as vehicles. When only the local sources of air pollution in Delhi are assessed, and contributions from external sources are excluded, the transport sector emerges as the biggest contributor, accounting for more than half of the pollution coming from only the local sources, says the CSE analysis.
“Usually, every year, the contribution of farm fires to Delhi’s air quality during this first phase of winter is considered the biggest problem, detracting attention form the local sources of air pollution. But this year, the air quality of Delhi has turned from poor to very poor even when for most part of this phase, the contribution of farm fires has remained less than 1 to 3 per cent, reaching up to 8-16 per cent only on two days. This exposes the problem of higher contribution of local air pollution sources,” says Anumita Roychowdhury, executive director, research and advocacy, CSE.
“What is stunning is the very high contribution of vehicles among the local sources of Delhi, to Delhi’s air quality – it is more than half. With the overall number of farm fire count declining, the city cannot hide behind its smokescreen anymore. This demands very stringent advanced action at scale and with speed to minimise the local pollution in Delhi and its surrounding region,” she adds.
The CSE analysis has come at the onset of winter and just before the anticipated peaking of episodic air pollution from stubble burning and bursting of firecrackers during Diwali. “It focuses on current trends in PM2.5 levels to understand the nature of the change in air quality and the changing pattern of the contribution of different sources of air pollution to overall particulate pollution in Delhi,” says Shambhavi Shukla, programme manager, clean air programme, CSE.
Shukla adds: “The PM2.5 levels during this phase of winter of 2024 appear to be similar and even higher compared to the same time frame during the previous winters — suggesting that air quality has not improved substantially and is at risk of worsening.”
“An added challenge has been the escalation in congestion index of major roads across Delhi, that has further aggravated the pollution exposure. Vehicles caught in congestion and idling emit several times more than their normal on-road emissions,” say Shubham Srivastava, programme officer, clean air programme, CSE; Srivastava has analysed the traffic congestion in Delhi.
The methodology
This analysis focuses on PM2.5 concentration trends from September 15 to October 28, 2024, and also compares this time frame with the corresponding time zone during the past years.
This analysis has been done is based on the following:
Publicly available granular real time data from the CPCB’s official online portal, Central Control Room for Air Quality Management. The data has been captured from 37 official stations under the Continuous Ambient Air Quality Monitoring System (CAAQMS) spread across Delhi.
Dynamic estimation of real-time data on source contribution by the Decision Support System for Air Quality Management of the Indian Institute of Tropical Meteorology (IITM) to assess the real-time trend in the relative contribution of different sources of pollution.
Farm fire counts from the Indian Agricultural Research Institute (IARI) and contributions from farm stubble fires to Delhi’s air quality, as estimated by the Ministry of Earth Science’s SAFAR (System of Air Quality and Weather Forecasting and Research).
Additional analysis has also been done to assess the change in traffic speed in the city –a measure of congestion during early winter (September 15-October 27, 2024) — on 15 stretches of key roads in Delhi, and relate it with the pollution trends.
The key highlights of the CSE assessment
Air quality trends at the onset of winter – steady deterioration: Delhi’s air quality has begun its seasonal incline, with PM2.5 levels surpassing 100 microgramme per meter cube (µg/m³) on October 14. While this level remains lower compared to previous years, it is expected to climb sharply in the coming days. The highest PM2.5 spike this early-winter season (Sept 15-Oct 28) was recorded on October 23, reaching 213 µg/m³ when the contribution of farm fire was 16 per cent. However, the average PM2.5 level during October 1 to October 28 shows an increase of about 13 per cent compared to the corresponding period in 2023.
In the first phase of this winter season, more very poor and poor air quality days have been recorded, while the number of good air quality days have reduced drastically: Eleven ‘very poor’ air days were recorded during the period under scrutiny – which is highest for the same period in the last three years. During the pre-Diwali period under scrutiny this year, 11 days have were ‘very poor’ air quality days and five were ‘poor’ days. Altogether, there were 16 ‘very poor’ and ‘poor’ days this season, up from 13 days in each of the previous two years. In contrast, the same period in 2022 and 2023 had recorded seven ‘very poor’ days each.
“Conversely, ‘good’ air quality days have sharply declined, dropping from 11 days in 2022 to just two in 2024,” says Sharanjeet Kaur, programme officer, urban lab, CSE, who has analysed the air quality data.
What is contributing to Delhi’s PM2.5 concentration now? CSE has analysed the real time dynamic estimation of the relative contribution of different pollution sources to Delhi’s air quality put out by the IITM’s Decision Support System (DSS). The DSS provides insight into the fractional contribution to PM2.5 in Delhi from 29 sources, out of which eight are in Delhi (local sources) and the rest are outside Delhi. This analysis has selected eight sources that the DSS has attributed as local sources for Delhi.
CSE has accessed the data for every day for the period October 12-27 (24-hour average). Contribution of each local source of pollution has been assessed. These pollution sources include transport, industry, construction, waste burning, energy, residential source, road dust and other group of sources.
Nature of influence of sources from outside Delhi: During this phase, the overall contribution of farm fires has remained only 4.44 per cent. But there has been substantial intrusion from the surrounding region of Delhi – amounting to 66 per cent – implicating a wide range of other sources of pollution. The contribution from “other districts” include that from districts of Haryana, UP, MP, Bihar, Rajasthan, etc that are outside the NCR. This demands a region-wide and airshed-based mitigation strategy.
Vehicles are the highest contributor among the local air pollution sources in Delhi: When only the local sources of air pollution in Delhi are assessed, (and contributions from outside sources are excluded), the transport sector contribution is more than half of the pollution coming from only the local sources. This is followed by residential burning, which is 13 per cent, followed by industry at 11 per cent, construction at 7 per cent, energy at 6 per cent, waste burning at 5 per cent, and road dust and others at 4 per cent each.
Lesser impact of farm fire on Delhi’s Air Quality: So far this year, farm fires have had a minimal impact on Delhi’s air quality, with their contribution to PM2.5 levels remaining below 1 per cent until October 20, despite relative increase in fire counts during the period. As October progressed, there was a noticeable increase in the fire count, peaking between October 22 and October 25.
During this period, the contribution of farm fires to Delhi’s PM2.5 levels rose, reaching a peak of approximately 16 per cent on October 23. However, this influence quickly subsided, dropping to 3 per cent by October 27. This has been happening due to changing wind directions from the north-westerly direction during the days, leading to higher contribution from stubble burning between October 21 and 25. This direction has again changed to south-easterly, leading to lesser contribution of stubble burning to Delhi’s PM2.5 levels.
Between October 10 and October 28, 3,264 burning events were detected in the four states: these are distributed as 1,870, 843, 539, and 12 in Punjab, UP, Haryana and Delhi, respectively.
Unlike previous years, the smoke from farm stubble fires has not overwhelmed the region’s air quality yet.
High traffic build-up before Diwali worsens congestion and pollution impacts: CSE has analysed hourly travel time data for 25 road stretches in Delhi for a period of 45 days (September 15 to October 29) provided by a popular web navigation and transportation service, Google Maps API, to analyse the Speed Reduction Congestion Index in Delhi. The Speed Reduction Index measures the reduction in speed on congested roads compared to free-flowing traffic conditions, and is directly proportional to the Congestion Index in the region.
The goal was to understand variations in traffic flow captured during peak and off-peak hours, gaining insights into how congestion evolves throughout the day. It was also analysed how congestion is impacted by major festivals.
The road stretches studied were chosen after consulting several sources of literature available on the most congested areas in Delhi. Among these, the latest and most frequently referenced were the “Report of High-Powered Committee on Decongesting Traffic in Delhi” made publicly available in 2021, and the 2023 Delhi Traffic Police report on congestion hotspot identification.
The study was conducted by choosing the most congested samples based on literature, irrespective of an equal share of routes studied in each zone. The resultant geographical distribution and expanse for the routes is as follows: out of the 25 road stretches, nine fall under Central Delhi Zone, two each in the North and West Zones, six in South Delhi Zone, five in South-East Zone and three in the New Delhi Zone (includes the cantonment area).
The results are recorded to show variations in four time frames: 1) Entire period of 45 days (September 15-October 29), 2) A regular week (chosen as September 23-29) 3) Dussehra week (October 5-12), and finally the Diwali week (October 26-29).
Substantial build-up of congestion: During the entire period under scrutiny, an average speed reduction of 40.8 per cent has been observed in the weekday morning peaks and 57.9 per cent in the evening peaks. During weekends, a 27.6 per cent speed reduction occurs in the mornings, while 42 per cent reduction occurs during the evening.
Geographically, the West and South Zones in Delhi are the most vulnerable, with 27 per cent and 30 per cent incidences of all highest congestion indices during the period.
During the festival week preceding Diwali, the average increase in congestion during morning peaks on a weekday is 4 per cent, with some stretches suffering congestion index increase of 7-8 per cent. During evening peaks, the average increase was 7 per cent, with maximum increase recorded up to 15 per cent.
The weekend approaching Diwali is by far the most congested weekend during the entire period. It is unusual to see an average speed reduction of more than 25 per cent during weekend mornings, however for the first time in the last month and a half the average reduction has been over 30 per cent (at least 5 per cent higher congestion than a regular weekend); on some stretches, it even crossed the 60 per cent speed reduction mark. Similarly, during weekend evenings that approached Diwali, a 7-10 per cent increase in congestion was observed.
Hourly nitrogen dioxide levels correlate well with congestion in the city: It is well known that vehicles caught in congestion and idling can spew emissions several times higher than their normal emissions on roads. Considering that vehicles are the dominant sources of nitrogen oxide levels, there is a strong co-relation between vehicles and hourly changes in NOx levels. The daily accumulation of pollution is significantly affected by peak traffic hours. The hourly level of NO2 has correlated with the congestion levels, though there has been some dilution due to dispersion during the afternoon. Hourly NO2 levels during evenings could be high, ranging between 54 µg/m³ to 75 µg/m³. This is the time when congestion is also high.
A comparison of traffic on specific days revealed that congestion was highest in the weekend before Diwali (October 27). During this time, the hourly concentration of NO2 was notably elevated, peaking at 61 µg/m³ in the morning when traffic speed averaged 31 km/h, and reaching 75 µg/m³ in the evening with a reduced traffic speed of 21 km/h. Notably, even at midnight, the concentration of NO2 remained elevated at 68 µg/m³.
Pollution hotspots continue to remain problematic: All 13 official air pollution hotspots in Delhi have shown a rise in PM2.5 levels this October compared to the same period in 2023, except Mundka and Bawana, which demonstrated improvements of 12 per cent and 7 per cent, respectively. Despite this progress, Bawana remains a major concern, recording the second-highest PM2.5 levels in the past week (Oct 21-28) with an average of 201 µg/m³. Burari Crossing led the list, averaging the highest PM2.5 concentration at 204 µg/m³, followed closely by Bawana and Jahangirpuri, both at 201 µg/m³. All official hotspots have remained above the critical threshold of 100 µg/m³.
On an annual average, Anand Vihar ranks as Delhi’s most polluted hotspot in 2024, with a PM2.5 level of 111 µg/m³, followed by Jahangirpuri at 102 µg/m³. Nehru Nagar and Vivek Vihar have emerged as new pollution hotspots, each averaging 92 µg/m³ in PM2.5 concentration.
The take-aways from the study
This time, the seasonal surge in PM25 levels during the early phase of winter in Delhi is not hugely impacted by the farm fires that have begun to decline. But the impact of the local sources of air pollution in Delhi and the surrounding regions dominates and is much bigger.
Among the local sources, contribution of the vehicular emissions to daily PM2.5 levels is maximum followed by residential solid fuel burning and industrial sources. This is evident from the official estimates of IITM.
Says Roychowdhury: “It is clear that while action on farm fire needs to get more aggressive and impactful to eliminate the problem, the seasonal episodic pollution cannot continue to mask and hide the significant contribution of local pollution sources and sources from the surrounding regions. Clean air benchmark cannot be met and sustained throughout the year without stringent and upscaled action targeting the key sources of pollution including vehicles, industry, solid fuels, waste burning and construction, among others. This immediately requires action taken report to identify the key gaps in action and the strategy to address this.”
The clean air action in Delhi and NCR requires massive upscaling of local and regional action to curb emissions from vehicles to increase the usage and share of integrated public transport services, walking, cycling and restraint measures to reduce usage of personal vehicles. This needs to be supported by upscaled and ambitious vehicle electrification strategy.
Roychowdhury adds: “Initiate stronger action to reduce/eliminate use of solid fuels, take stronger steps to scale up clean fuel transition and emissions control fro
m industries including peripheral industries and those in non-conforming areas, and ensure clean construction and elimination of garbage burning.”
