Sourabh Yadav says he has "forgotten what it's like to have a window open" at his home in Delhi.
Originally from Chhattisgarh, a small state in central India, the 26-year-old filmmaker moved to India's capital for university and has lived there for eight years.
"Summers are brutal in Delhi, so we try to go outside more during winters," he told the ABC.
"But now, given India's Air Quality Index (AQI), these little joys seem tarnished."
AQI is the system used to measure how polluted the air is and ranges from 0–50 for "good" to 500 for "severe".
Since November, Delhi's AQI has hovered between 300 and 400, more than 20 times the limit recommended by the World Health Organization.
Even the air inside Mr Yadav's home is poor, so he bought an air purifier.
"When I turned it on for the first time, it displayed a near 300 AQI. After a few minutes, it managed to go down to around 20," he said.
However, Mr Yadav said having an air purifier in Delhi was "a privilege" as they sell for between 10,000–20,000 Indian Rupee ($162–$340).
"That's around the cost of monthly rent in Delhi, even for middle-class people," he said.
"Having to pay that kind of money just to breathe is not always in people's capacity."
Money aside, Mr Yadav said air purifiers also had limitations.
"They only work for small spaces, which is why I keep it in my bedroom," he said.
"But as soon as I go into my living room or kitchen, I'll start to feel dizziness or get a headache.
"It means people will need multiple air purifiers in their home, which most cannot afford."
'Simple joys' come with health risks
Home to more than 30 million people, Delhi and its surrounding region routinely rank among the world's most polluted cities.
India has six of the 10 most polluted cities globally, and Delhi tops the chart, according to an October report from Switzerland-based air quality monitoring database IQ Air.
Each winter, farmers burn crop residue in nearby states and cooler temperatures trap the smoke that mixes with vehicle and industrial emissions.
India's Central Pollution Control Board reported some improvements in recent years due to favourable weather conditions and anti-pollution measures.
But some studies have found Delhi's air pollution has been more severe than previously estimated.
The poor air quality has impacted nearly all aspects of life.
Hybrid learning has become the norm at schools and universities, offices close regularly, and people mostly stay indoors.
Mr Yadav said he has also lost other "simple joys" in life, such as enjoying a roadside chai.
He said buying a chai at a "tapris" — roadside shops that sell tea — was part of his regular routine and a big part of Indian culture.
"But now standing on a footpath with your mask off to sip tea feels a little uneasy," he said.
Now Mr Yadav buys packed tea to have at home.
"Sometimes it makes you angry," he said.
"It makes me wonder, God, this air is the very life you breathe. How can you not care?"
Delhi's residents are fed up.
In November, hundreds gathered at Delhi's India Gate in a rare protest, urging authorities to act.
India's government has taken steps to address air pollution, one being its launch of the National Clean Air Program (NCAP) in 2019.
Its aim was to cut PM2.5 pollution by 20 to 30 per cent by 2024 — from 2017 levels — which was later revised to a more ambitious 40 per cent reduction by 2026.
However, policing Delhi's air quality will require an "inter-sectoral response" according to Poornima Prabhakaran, an epidemiologist and public health researcher at Ashoka University.
"This is due to the multiple sources of pollution," Dr Prabhakaran said.
"Transport is a major source, as well as industrial activity, road and construction and demolition dust.
"There must be a concerted effort to address all sources to begin to lower the hazardous levels of pollution."
Air pollution a silent killer
Delhi's air pollution is shortening the life expectancy of its residents by as much as 12 years, according to a recent Air Quality Life Index report by the Energy Policy Institute at the University of Chicago.
"What we generally see during poor air quality times is an increased number of patients who present to the hospital with exacerbation of their asthma or Chronic Obstructive Pulmonary Disease (COPD)," said Saurabh Mittal, an expert in diseases of the respiratory system at All India Institute of Medical Sciences.
"Young patients, who were previously asymptomatic, also come with eye, nasal and throat irritation and a persistent cough."
Dr Mittal said the pollution also had an impact on some people's mental health.
"Patients with psychological disorders can face low mood and more fatigue in poor air quality," he said.
And in the long term, there was a higher risk of cardiovascular and cerebrovascular disease, Dr Mittal added.
"Higher degree of hypertension and accelerated memory loss are some long-term effects as well," he said.
When breathing comes at a financial cost
Delhi resident Ashna Sharma and her family have struggled with respiratory issues for years.
"Stepping outside is nearly impossible, and inside our home every single room now has an air purifier," Ms Sharma said.
The 26-year-old counselling psychologist and content creator said she was "genuinely worried" about her health, but even more for her parents.
"They are ageing, and this is not the quality of life they deserve," she said.
Ms Sharma and her family have also racked up more bills as they cope with the air pollution.
"In just the last two months, we've spent more on medicines and doctor visits than anything else," she said.
"We can't even do something as basic as go for a walk."
Looking back over the years, Ms Sharma said the only time she remembers breathing clean air was during the COVID lockdown "when vehicles were off the roads".
"Between Diwali firecrackers, overpopulation, and stubble burning, Delhi has become almost unlivable," she said.
Cutting emissions 'at the source'
Critics say only long-term measures to cut emissions can bring real relief.
"Delhi's air improves only when emissions are cut at the source," said Roxy Mathew Koll, a climate scientist at the Indian Institute of Tropical Meteorology.
"These emissions are from industries, vehicles, waste and crop burning," Dr Koll said.
He said cuts in emissions must also be complemented by cleaner energy, efficient transport, and coordination with neighbouring states.
But Delhi's geography made this challenging, he said.
"Delhi sits in a basin between the Himalayas and Aravallis mountains where weak winter winds and temperature inversions trap pollutants near the surface," he said.
"These natural limits make emission control even more urgent, not less."
