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 average monthly air quality on the Air Quality Index (AQI) scale every month between October and February except one. This winter is no exception: as of mid-November, Delhi ranked among the most polluted major cities according to IQAir. However, recent evidence suggests that Delhi’s air pollution crisis is no longer confined to the winter months. 

Public and policy attention during the colder season typically focuses on the high levels of particulate matter (PM)—microscopic particles of dust, soot, and smoke that penetrate into the lungs. However, another key transport pollutant has been in the news lately, as nitrogen dioxide (NO₂) levels in Delhi have surged to three times the national safe limit and almost ten times the stricter World Health Organization guideline in several areas in November. Similar situation prevailed in the preceding years including 2023 and 2024 and the Ministry of Health and Welfare noted that higher NO₂ levels in Delhi were associated with increased emergency health visits. NO₂ is part of a group of gases known as nitrogen oxides (NO_x) that also includes nitric oxide (NO), another major air 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, which forms the protective ozone layer).  

Recent data from the Central Pollution Control Board (CPCB)’s submission to the National Green Tribunal (NGT) have highlighted a concerning rise in ozone pollution across Delhi NCR. Following a Centre for Science and Environment report, CPCB’s analysis of data from multiple monitoring stations revealed that Delhi NCR recorded the highest exceedances of ozone concentrations among Indian regions in 2023. Based on a 2% exceedance threshold—meaning ozone levels are above the limit for more than 2% of monitored hours—exceedances were observed at 25 of 57 locations in 2023, assessed on an 8-hour average. The situation has worsened in summer months: based on a 1-hour average, 2% exceedances were recorded at 21 locations in 2024, up from 6 locations in 2023.  

CPCB links this rise in ground-level ozone to complex reactions between NO_x (produced by transport, power generation, industry, and other sources) and volatile organic compounds—processes that intensify in heat and sunlight, making ozone pollution a particular concern during the summer. It is worth highlighting, however, that NO_x is a precursor to not just ground-level ozone but also to secondary PM—one of the multiple sources of pollution contributing to Delhi’s wintertime 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 shift focus toward 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’s leapfrog from BS IV to BS VI emission norms delivered substantial real-world emission reductions. For example, average NO_x and PM emissions from private cars fell by around 77% and 89%, respectively.  

Yet the study also identified high real-world NO_x emissions among commercial fleets, even in BS VI taxis and light goods vehicles, which emitted 2.4 and 5.0 times more NO_x, 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 NO_x emissions. Such gaps may stem from poor maintenance, degraded aftertreatment systems, and sustained high-load operation, among other factors. Identifying high-emitting vehicles using tools like 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 the tailpipe pollutants through forward-looking policy design.   

The next step will be to advance to zero-exhaust emissions transport like 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 to 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. ZEV sales requirements require 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 with ZEV mandates 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 as required by other types of regulations. This simplicity makes such frameworks particularly attractive for state-level or regional authorities, especially in Delhi NCR.

Globally, ZEV sales requirements have also sustained ZEV market growth in markets where vehicle purchase incentives have been reduced or ended, as evidenced by data from regions like California, China, Germany, and the United Kingdom. Measures like 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 NCR needs to shift from reactive, seasonal measures to a forward-looking, data-driven strategy to reduce transport emissions. Introducing ZEV sales requirements would be one way to build on that momentum. As winter gets underway again, the question should not be how to withstand the next few months of hazardous air—but how to break a cycle that now threatens public health year-round.