Every winter, the return of low wind speeds and temperature inversions in Delhi-National Capital Region (NCR) reignites the familiar debate on deteriorating air quality. From 2018 to 2024, Delhi recorded poor to severe air quality on the Air Quality Index (AQI) scale between October and February, every month except one. This winter is no exception. However, recent evidence suggests that Delhi’s air pollution crisis is no longer confined to the winter months.
Public and policy attention typically focuses on the high levels of particulate matter (PM) during winter. However, another key transport pollutant has been in the news recently: Nitrogen dioxide (NO₂) levels in several areas of Delhi surged to three times the national safe limit and almost ten times the stricter World Health Organization (WHO) limit in November. A similar situation prevailed in the preceding years. According to the Union ministry of health and family welfare, recent Indian Council of Medical Research’s study highlighted how higher NO₂ levels in Delhi were associated with increased emergency visits to hospitals.
NO₂ is part of a group of gases known as nitrogen oxides (NOₓ) which includes nitric oxide (NO), another major pollutant from vehicles. NO readily transforms into harmful NO₂ in the air, and this NO₂ also plays a key role in the formation of ground-level ozone — a secondary pollutant that is harmful to human health and the environment (unlike stratospheric ozone).
Recent data submission by the Central Pollution Control Board (CPCB) to the National Green Tribunal highlighted a concerning rise in ozone pollution across Delhi NCR. Following a Center for Science and Environment report, CPCB’s analysis of data from multiple monitoring stations revealed that, in 2023, Delhi-NCR recorded the highest ozone concentrations in breach of safe limits among all Indian regions. A 2% exceedence of the threshold — meaning ozone levels were above the safe limit for more than 2% of monitored hours — was observed at 25 of 57 locations in 2023, assessed on an eight-hour average. The situation worsened in summer months: Based on an one-hour average, 2% breach was recorded at 21 locations in 2024, up from six in 2023.
CPCB links this rise in ground-level ozone to complex reactions between NOₓ (produced by transport, power generation, industry, and other sources) and volatile organic compounds, among others — processes intensified by heat and sunlight, making ozone pollution a particular concern during the summer. NOₓ is a precursor to not just ground-level ozone but also to secondary PM — one of the many sources of pollution contributing to Delhi’s winter smog.
Short-term or reactive interventions, such as bans on firecrackers, AQI-based graded response action plan measures, or even cloud seeding, can only offer momentary relief. It is time to focus on long-term, structural solutions that address emissions at their root.
A 2024 remote sensing study by The Real Urban Emissions (TRUE) Initiative and the International Council on Clean Transportation (ICCT) demonstrated that India leapfrogging from BS IV to BS VI emission norms delivered substantial real-world emission reductions. For example, average NOₓ and PM emissions from private cars fell by around 77% and 89%, respectively.
Yet, the study also identified high real-world NOx emissions among commercial fleets, even in BS VI taxis and light goods vehicles, which emitted 2.4 and 5.0 times more NOₓ, respectively, than private cars. While the shift to compressed natural gas (CNG) for commercial vehicles has helped reduce PM emissions, CNG commercial fleets still exhibited high real-world NOₓ emissions. Such gaps may stem from poor maintenance, degraded after-treatment systems, and sustained high-load operation, among other factors. Identifying high-emitting vehicles using tools such as remote sensing and taking corrective action through inspection, repair, or targeted enforcement will be crucial for addressing pollution from vehicles currently on the road.
While strengthening compliance and enforcement remains critical, vehicular emissions control must shift to tackling tailpipe pollutants through forward-looking policy design. The CNG transition for commercial fleets in Delhi and the nationwide BS VI leapfrog show India’s ability to act decisively.
The next step will be to advance to zero exhaust emissions transport such as electric vehicles (EVs), especially in Delhi NCR where pollution levels demand faster and deeper action than anywhere else in the country. Delhi has a progressive EV policy that has primarily relied on demand-side incentives for EV buyers and charging providers, helping EVs reach about 11% of new vehicle registrations in 2024 and around 14% as of October 2025. However, this remains well below the initial policy target of 25% of all new registrations by 2024.
While fiscal incentives have been effective, scaling them up to induce mass-market adoption would require substantial financial resources. In this context, supply-side regulations, which focus on manufacturers rather than consumers, can deliver emissions reductions and help spur India’s EV manufacturing industry — all at a low cost incurred by the government. Supply-side regulations work by shaping what manufacturers produce, ensuring cleaner technologies reach the market.
A recent ICCT publication examined how one kind of supply-side regulation — zero exhaust emission vehicle (ZEV) sales requirements — can accelerate the transition to ZEVs in India. These requirements mandate manufacturers to sell a rising share of zero-exhaust emission vehicles each year, encouraging investment and providing a predictable environment for developing supply chains. Monitoring compliance is also administratively simple: Regulators only need to track the number of ZEVs sold each year rather than assess complex technical parameters for every vehicle. This simplicity makes such frameworks particularly attractive for state-level or regional authorities, especially in Delhi NCR.
Globally, ZEV-sales requirements have also sustained market growth in jurisdictions where vehicle purchase incentives have been reduced or ended, as evident in California, China, Germany, and the UK. Measures such as these are not just beneficial for air quality but also for consumers, promoting continued investments in charging infrastructure and the development of more diverse and affordable model offerings.
Delhi and the larger NCR must adopt a forward-looking, data-driven strategy to reduce transport emissions. The question should not be how to deal with the next few months of hazardous air, but how to break a cycle that now threatens public health year-round.
Anirudh Narla is researcher, and Amit Bhatt is managing director (India), ICCT. The views expressed are personal
