Delhi's toxic winter air returns as four-month Winter Action Plan runs from 1 November to 28 February

India's capital Delhi is again facing grey haze and toxic air at the start of winter. People exercised in a park on Thursday breathing in hazy, polluted air, while residents said mornings have already started feeling stuffy indoors.

Delhi teacher Meenu Rana, 43, keeps two cardboard boxes in her living room — one filled with Diwali decorations and twinkling lights, the other holding air purifiers. She said the mornings have already started feeling stuffy and it will get worse in the coming days, so it is better to be prepared.

Delhi and its satellite cities record some of the world's highest pollution levels through the year. As winter sets in, falling temperatures and slower winds trap pollutants close to the ground. Smoke from crop residue burning in neighbouring states adds to emissions from vehicles and factories and construction dust, while firecrackers during festivals often worsen air quality.

This year, the Delhi government announced its Winter Action Plan months before the worst smog arrived. The plan is in place from 1 November to 28 February, covering the months when pollution usually spikes.

Experts called this a step in the right direction, noting previous measures were often rolled out only after air quality became too bad to ignore. However, they said the plan by itself will not be enough and called for more holistic, long-lasting measures.

Just days after the plan came into effect, the city is slipping back into a familiar pattern. A grey haze hangs over Delhi this week with a distinct smoky smell. People complain of irritation in their eyes and difficulty breathing, and coughs and sneezes are heard everywhere.

For those who can afford them, air purifiers have become a household necessity. Outdoors, people wear masks or cover their faces with cloth.

Tackling pollution was among the promises made by the governing Bharatiya Janata Party during its election campaign last year, making the winter plan a major test of that pledge.

The plan restricts entry of older, more polluting vehicles registered outside Delhi and denies fuel to vehicles without a certificate showing they meet emission standards. Demolitions and outdoor construction work that generate dust have been temporarily banned.

To discourage private vehicle use, the government has asked offices to allow half their employees to work from home, introduced staggered office timings for its staff and doubled parking charges. It says it will strengthen pollution monitoring and enforcement and promote public transport and electric vehicles.

These measures are separate from the Graded Response Action Plan, overseen by the federal Commission for Air Quality Management. Grap introduces restrictions in stages as pollution rises. This week its second stage is in force, restricting diesel generators and burning of coal and firewood.

Experts say the actions collectively provide a roadmap on paper, but success depends on enforcement. Parthaa Bosu, strategic adviser at the Environmental Defense Fund, said there are a lot of positive changes in planning, but in execution the position probably still stands at the same level.

Manoj Kumar, an analyst at the Centre for Research on Energy and Clean Air, said targets must be set for every sector — including power generation, industry and transport — not just vehicle entry, construction and stubble burning. He said the contribution of each sector and state is known, so targets can be set to reduce emissions from each over the next five years.

Bosu pointed to secondary pollutants, when gases react with sunlight, water vapour and other substances to form harmful particles. He said pollution is not just caused by biomass burning or vehicles; dust from the ground, coal and fly ash, materials burned at brick kilns and large-scale burning of urban waste also contribute, and much of this is still not being stopped.

Delhi's problem is also affected by pollutants travelling in from neighbouring states and other parts of northern India, Bosu explained. Measures taken by Delhi alone can achieve only so much, and neighbouring states and the wider northern region must work together.

During winter, government monitoring stations in Delhi frequently record Air Quality Index readings above 300, classified as very poor. On particularly bad days readings can reach 500, the highest point on India's scale — not because pollution cannot rise further, but because domestic trackers do not record beyond it. Swiss-based IQAir has recorded readings close to 1,000 on some days.

The World Health Organization recommends average PM2.5 levels over 24 hours should not exceed 15 micrograms per cubic metre. In Delhi, levels are often more than 25 times that limit during pollution season.

Dr Manoj Goel, pulmonology unit head at Fortis Memorial Research Institute near Delhi, said these tiny particles can penetrate deep into the lungs and enter the bloodstream, triggering inflammation and affecting multiple organs. Even short-term exposure can cause throat irritation, coughing, wheezing and breathlessness, and worsen existing heart and lung conditions.

A 2025 report by the Energy Policy Institute at the University of Chicago estimated air pollution could reduce life expectancy in Delhi by up to 8.2 years.

Restrictions also disrupt everyday life. Delhi is closely connected to satellite towns Noida and Gurugram, with thousands travelling between them daily for work. Long queues form at city borders as vehicles are stopped and checked, leaving commuters stuck for hours.

Rana keeps her windows closed and curtains drawn and has added more indoor plants. Her family dreads another winter but is not planning to move. She said she would have left long ago had there been an option, but her son's school and both parents' jobs make it practically impossible, so they will have to live with it.