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Air quality in Delhi has gone from bad to worse in the past few days. The reason though is not farm fires, as one would expect, but high contribution of local air pollution sources such as vehicles according to a new pre-Diwali and pre-winter analysis of air pollution in Delhi by the Centre for Science and Environment (CSE).
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, according to the 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,” Anumita Roychowdhury, executive director, research and advocacy, CSE, said in a statement.
“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 added.
The analysis by CSE comes 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,” Shambhavi Shukla, programme manager, clean air programme, CSE, said in the statement.
“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,” she added.
“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,” said Shubham Srivastava, programme officer, clean air programme, CSE; Srivastava has analysed the traffic congestion in Delhi.
The analysis focused on PM2.5 concentration trends from September 15 to October 28, 2024. It also compared this time frame with the corresponding time zone during the past years.
For conducting the analysis, the researchers used publicly available granular real time data from the Central Pollution Control Board’s official online portal, Central Control Room for Air Quality Management.
They also used data related to farm fire counts from the Indian Agricultural Research Institute 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 was also 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 researchers also analysed the real time dynamic estimation of the relative contribution of different pollution sources to Delhi’s air quality put out by the Indian Institute of Tropical Meteorology’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,” the statement noted.
The team found that for the period October 12-27, farm fires on average contributed only 4.44 per cent to PM2.5 levels in Delhi.
But there was 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,” the statement read.
But when only the local sources of air pollution in Delhi were assessed, the transport sector contributed more than half of the pollution coming from only the local sources.
This was followed by residential burning at 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.
“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,” said Roychowdhury.
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 added: “Initiate stronger action to reduce/eliminate use of solid fuels, take stronger steps to scale up clean fuel transition and emissions control from industries including peripheral industries and those in non-conforming areas, and ensure clean construction and elimination of garbage burning.”