Delhi’s air quality discourse has long been dominated by seasonal explanations such as farm fires, unfavourable meteorology, and pollution blowing in from outside the city. While these factors do influence short-term air quality, emerging evidence increasingly shows that Delhi’s pollution burden is now largely self-driven, with local sources playing a growing and persistent role. Among these, vehicles are a dominant source of pollution, particularly during winter, when air quality is worst.
This shift has important implications for how Delhi frames its response. Episodic measures triggered during severe pollution episodes are insufficient when the problem is rooted in everyday mobility choices, vehicle growth, congestion, and fossil-fuel dependence. The data now points to a clear conclusion: Delhi’s air quality challenge is no longer episodic — it is systemic.
One of the most important advances in recent years has been the availability of dynamic, real-time source contribution data through the Decision Support System (DSS) for Air Quality Management, developed by the Indian Institute of Tropical Meteorology (IITM). This system estimates the relative contributions of 29 pollution sources to daily PM2.5 levels in Delhi, distinguishing between local sources within Delhi and external contributions from the surrounding region.
CSE’s analysis of this real-time DSS data for the winter period from November 10 to 20 for three consecutive years, 2023-25, shows a striking pattern. When only Delhi’s local sources are considered — excluding pollution transported from outside — vehicles alone contribute more than half of the PM2.5 pollution, averaging 51-53 per cent of local emissions. This period was selected to study the peaks of stubble burning and to align with comparable data from three consecutive years.
This means that, even before accounting for regional inflows, Delhi’s pollution profile is overwhelmingly shaped by transport emissions. During winter, when dispersion is poor and the mixing height is lower, the impact of these emissions intensifies— especially during peak traffic hours.
The DSS is not a substitute for detailed source apportionment studies, but it plays a crucial complementary role. Unlike one-time studies, the DSS provides continuous insight into trends, helping policymakers understand how different sources behave, especially during winters with unfavourable meteorological conditions.
Long before real-time DSS data became available, multiple source apportionment and emission inventory studies had already identified transport as one of Delhi’s most significant pollution sources.
Studies conducted by IIT-Kanpur (2015), TERI-ARAI (2018), and SAFAR-IITM (2018) estimate the transport sector’s contribution to the PM2.5 emission inventory at 20 per cent, 39 per cent, and 41 per cent, respectively. Across these assessments, vehicles consistently emerge as the largest combustion-related source and the second-largest overall contributor, after dust.
Notably, the IIT-Kanpur source apportionment study shows that during winter, when the city experiences its most severe pollution episodes, the relative contribution of vehicles increases further, as dust declines and combustion sources dominate.
Together, these studies leave little room for ambiguity: vehicles do not marginally contribute to spikes — they persist as a year-round source of pollution, with amplified impacts during winter.
CSE’s analysis of DSS data for November 10-20 across 2023, 2024 and 2025 reveals a worrying trend. Delhi’s pollution burden is becoming increasingly local, even as regional inflow fluctuates.
In 2025, local sources contributed nearly 35 per cent of PM2.5, up from 27.3 per cent in 2024. At the same time, the contribution from surrounding National Capital Region districts declined from 36 per cent in 2023 to about 25.8 per cent in 2025. This indicates that Delhi can no longer rely on reductions in regional pollution to offset its own emissions.
Stubble burning, often blamed for winter smog, varies sharply year to year — rising in 2024 but falling in 2025. Notably, the increase in local pollution in 2025 occurred even though stubble burning contributions during this period were comparable to those in 2023. This trend confirms that farm fires act as a seasonal stressor rather than a consistent or dominant force shaping Delhi’s air quality.
What remains consistent is transport. Across years, vehicles contribute roughly 51-53 per cent of Delhi’s local pollution, making transport the single largest local source. In absolute terms, vehicular contribution peaked again in 2025, reversing the temporary dip seen in 2024.
Other local sources are also creeping up — residential emissions, construction activity, and waste burning show little improvement — but none rival the scale or persistence of transport emissions.
CSE’s recent analysis highlights another critical but under-discussed dimension of Delhi’s air pollution: the synchronised rise of PM2.5 with nitrogen dioxide (NO2) and carbon monoxide (CO).
During winter, PM2.5 levels rise and fall almost in tandem with NO2 during morning (7-10 AM) and evening (6-9 PM) traffic peaks. While NO2 exhibits sharper spikes associated with vehicular plumes, PM2.5 accumulates more slowly and disperses later, thereby prolonging exposure.
Carbon monoxide — a highly toxic pollutant predominantly emitted by vehicles — has shown widespread exceedances across Delhi yet receives little policy attention. Together, PM2.5, NO2 and CO create a toxic cocktail that reflects the dominance of combustion and traffic emissions.
This pattern exposes a hard truth: Delhi can no longer hide behind the smokescreen of farm fires. Even in winters with lower stubble burning influence, air quality remains in the “very poor” to “severe” range because local emissions continue unabated.
Parliamentary committee deliberations reflect an acknowledgement that vehicular pollution is a central concern. Several measures have been initiated: restricting intercity buses to BS-VI diesel, CNG, or electric modes; mandating only CNG- or electric-auto-rickshaw registrations; phasing out diesel autos; enforcing end-of-life vehicle regulations; expanding scrapping infrastructure; strengthening PUCC regimes; and scaling up electric bus deployment.
There has also been progress in fleet cleaning. Since 2015-16, all newly registered vehicles have been predominantly BS-VI compliant. The share of diesel cars in new registrations has declined substantially, and commercial fleets have shifted significantly toward CNG. These are essential gains and demonstrate that regulatory mandates do work when enforced consistently.
However, the committee notes that EV adoption remains below targets, congestion persists, and fitness-testing systems need strengthening. It has rightly recommended moving away from sweeping age-based bans towards performance-based identification of high-emitting vehicles, supported by advanced testing mechanisms.
What is missing is scale and integration. Measures remain fragmented, slow to expand, and insufficiently aligned with land-use planning, public transport expansion, and demand restraint.
Under the National Clean Air Programme (NCAP), Delhi had received Rs 81.36 crore by December 2025 but had utilised only Rs 14.1 crore — just 17 per cent of the funds released.
Low utilisation reflects deeper governance challenges, delayed project planning, weak inter-departmental coordination, and a preference for short-term measures over structural investments. Without effective deployment of funds, mandates remain on paper, and air quality outcomes stagnate.
Delhi’s air pollution crisis cannot be resolved through episodic bans or incremental tweaks. What is needed is a mandate-driven, system-wide transformation, especially in the transport sector.
CSE recommends prioritising ambitious, time-bound electrification targets across all vehicle segments supported by fleet renewal and scrappage of older vehicles, scaling up integrated public transport with reliable last-mile connectivity alongside walking and cycling infrastructure to shift commuters away from personal vehicles, restraining personal vehicle use through parking caps, rational pricing and congestion charges, reforming transport taxation to reflect the true social and environmental costs of vehicle ownership and use, addressing urban freight emissions through cleaner fuels and electrification, shifting budgets away from road expansion towards public transport, active mobility and zero-emission systems, and adopting measurable, verifiable monitoring systems that track real emission reductions rather than just compliance actions.
External or episodic factors no longer dominate Delhi’s air pollution problem. It is increasingly driven by everyday vehicle emissions, reinforced by congestion, fossil-fuel dependence, and insufficient restraint on personal mobility.
The data is unequivocal. The mandates exist. What is missing is the political and administrative resolve to scale solutions at the pace the crisis demands. Without this shift, Delhi’s air quality will remain trapped in a cycle of winter emergencies and short-term fixes — even as the city’s own emissions continue to rise.