DELHI – India’s Commission for Air Quality Management (CAQM) has identified the main sources of Delhi’s severe air pollution and admitted that there are critical gaps in current control measures, in response to a deadline set by the Supreme Court. 

The report, completed in a fortnight, synthesises findings from multiple research institutions to create the first unified assessment of what is polluting the capital. 

The Supreme Court-mandated report reveals that the city’s main air pollution sources are: transport (23%), secondary particulates (27%), and dust (15-27%). Winter PM2.5 levels are 35 times the World Health Organization (WHO) guidelines, despite decade-long efforts.

The report comes after the Supreme Court criticised CAQM on 2 January, for delays in identifying causes and finding long-term solutions to Delhi’s “worsening” air quality.

What sets this report apart from earlier studies is that it synthesises previous assessments to arrive at one unified set of numbers. The agency achieved this by bringing together researchers from government agencies, Indian Institutes of Technology, research institutes, NGOs and think-tanks.

The Chief Justice of India criticised the CAQM earlier this year, saying that it “appears to be in no hurry either to identify the causes or to find long-term solutions” to Delhi’s pollution.

The court added that the CAQM is obligated to bring domain experts together to arrive at a uniform and unanimous opinion on the causes of the “worsening” air quality.

Government concedes major gaps 

The CAQM’s report is also significant because it concedes several critical gaps in Delhi’s pollution control efforts. These range from conceding that PM2.5, or fine particulate matter pollution, is the “worst” pollutant to accepting that the pollution-under-control (PUC) certificates don’t check all key pollutants emitted by vehicles.

The panel included experts from government institutions as well as independent research organisations, including the Centre for Study of Science, Technology and Policy (CSTEP), Council on Energy, Environment and Water (CEEW), Urban Emission, Centre for Science and Environment (CSE) and The Energy and Resources Institute (TERI). 

The report has released two important data sets. The first shows that there has been a decline since 2016 in the annual average level of PM2.5. But the trendline (in blue in the chart below) has been almost flat since 2019, the year that the Indian government launched the National Clean Air Programme (NCAP).

Delhi’s PM2.5 air pollution has hovered around 100 micrograms per cubic metre for the last seven years, which is 2.5 times India’s safe standard but 20 times the WHO’s safe guidelines.

Main sources of Delhi’s air pollution

Delhi’s air pollution in winter and summer is starkly different, with winter pollution being more than twice as severe.

The largest contributor to Delhi’s winter PM2.5 pollution is secondary particulate matter (27%), tiny particles formed in the air from gaseous emissions from vehicles, industries, and biomass burning.

Among primary sources, transport vehicles contribute 23% while biomass burning, including burning solid fuels for cooking and warmth and crop residue burning, adds 20%. Dust from roads, construction, and demolition accounts for 15%, and industrial emissions contribute 9%.

In summer, dust becomes the dominant source, causing 27% of PM2.5 levels, driven by dry conditions and construction activity. Transport contributes 19%, secondary particulate matter causes 17%, and industrial emissions rise to 14%. Biomass burning drops to 12% during this period.

Delhi’s average winter PM2.5 concentration is 178 micrograms/m³, which is more than 35 times the WHO safe guideline of 5, and over four times India’s national standard of 40. Summer levels average 73, which is still nearly 15 times the WHO guideline and almost double the Indian standard. Data is based on 2021-2025 measurements.

However, CAQM says that the number of days where pollution was below the daily national standard of 60 micrograms has increased from 97 days in 2018 to 156 in 2025.

Why is transport so high?

The report points out that transport “repeatedly emerges as the most prominent pollution source within Delhi”. The transport source category includes off and on-road vehicles; petrol, diesel and CNG-powered vehicles.

There are several sources and reasons for vehicular pollution being so high:

• Older fuel standards: Bharat Stage (BS) 4, 3, 2, 1 and pre-BS vehicles are more polluting than the latest, BS 6 standard.
• Older vehicles: Particularly those operating beyond their regulatory lifespan of 10 or 15 years – for petrol and diesel respectively – are more polluting due to engine deterioration and compromised emission control performance.
• Fuel type: Diesel vehicles are a major source of particulate matter and oxides of nitrogen and sulphur, whereas CNG vehicles predominantly emit oxides of nitrogen.
• Traffic congestion: Pollution is determined not just by technology but also by driving conditions. Congested and slow-moving traffic leads to inefficient combustion, resulting in higher emissions per vehicle, whereas operation at optimal speeds enables more efficient combustion and lower emission rates.

Government admits critical gaps 

Significantly, the report concedes several gaps in controlling pollution. Presenting these gaps in a report for the Supreme Court is important because these have rarely been acknowledged at such a high level.

First, the report admits the current pollution checks or PUC certificates are “not a true representative of emissions” as they don’t measure particulate matter pollution – although this has been cited repeatedly by the Delhi local government as a measure that controls pollution.

Second, it accepts that PM2.5 is the most prominent pollutant that determines Delhi’s air quality index (AQI). This is in sharp contrast to the NCAP, which prioritises the reduction of PM10, not the more lethal PM2.5. Delhi government also has a push to reduce PM10, primarily dust, through the use of hundreds of expensive water sprinklers.

Third, the report says that data on the sources of pollution in Delhi’s larger neighbourhood (NCR) is sparse, so the report’s meta-analysis is taken as indicative.

Fourth, the supply of grid electricity across Delhi’s neighbourhood is “unreliable” which is why the use of diesel generators (DG) has increased substantially. It calls older or poorly maintained DGs “super-emitters” and warns that they result in direct, ground-level exposure to emissions.

Around 6 to 11% of Delhi’s air pollution is caused by “other” sources. These include cremations where wood is used, hotels and restaurants which use solid fuels like wood and coal, aircraft emissions during taxiing, landing and take-off, and brick kilns in and around Delhi.

Depending on the season, they are equally dangerous because they create local hotspots close to residential areas. These are a significant challenge because the CAQM says these are highly sensitive to enforcement.

What’s the plan to cut Delhi’s pollution?

The CAQM has asked four institutes, three of them government-backed, to develop a new emission inventory – a database of how much pollution is being pumped into the air and from which sources.

This study will be led by the Automotive Research Association of India (ARAI), which may raise some questions about a conflict of interest. While the association is under the government’s administrative control, many ARAI officials and members are from major vehicle manufacturers. Given that vehicles are a significant source of pollution, this could compromise ARAI’s ability to assess vehicular pollution. 

The other three institutes are IIT-Delhi, the Indian Institute of Tropical Meteorology (IITM, Pune), and The Energy and Resources Institute (TERI).

Air pollution beyond Delhi

This new push by the Supreme Court to improve Delhi’s air quality could have lessons for the wider area of north India or the Indo-Gangetic Plains (IGP), which the CAQM calls an emissions hotspot. This is 18% of India’s landmass, home to 40% of the country’s 1.4 billion population, and accounts for 35% of the emissions.

A still wider picture comes from the World Bank’s new report, A Breath of Change: Solutions for Cleaner Air in the Indo-Gangetic Plains and Himalayan Foothills. 

Almost a billion people across five countries – Bangladesh, Bhutan, India, Nepal, and Pakistan – live in this area, and around one million people die prematurely every year from polluted air. 

The World Bank calls for regional cooperation, which is easier said than done in one of the world’s most geopolitically sensitive neighbourhoods.

India’s capital is roughly in the centre of this region. Fixing Delhi’s air can provide a template and impetus to go big.

Image Credits: Chetan Bhattacharji.