Naresh Kumar Rana's day begins early. Every morning, he leaves his home at 6.30 a.m. and will drive across the vast Indian capital of Delhi for the next 10 hours.
Rana, 42, is an auto rickshaw driver. The three-wheeled taxicabs, with their distinctive green and yellow livery, are a common sight on the streets of Delhi, where they provide a cheap and ready available means of transport on the city's heavily congested roads.
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The job provides Rana with a steady income to help support his family, but it comes with a risk -- especially during winter -- when the city's already toxic air becomes even more lethal.
On Thursday morning, the day after Diwali, the Hindu festival of lights that is celebrated with fireworks, parts of the capital reported levels almost 40 times those considered "safe" by the World Health Organization.
"I have trouble breathing. By the time I return home, I have chest pain, I'm coughing," Rana, who has been a auto rickshaw driver for 24 years, told CNN of his experience driving during the winter smog.
"Now, when I cough, I assume it is because of the pollution."
Worst in the world
Pollution in India is believed to be responsible for up to a million deaths a year. In Delhi, where the air is ranked among the the worst in the world, the risks are particularly acute for those whose jobs require them to be outdoors.
"What are our lives worth? We're prone to having breathing problems because we drive for 14 to 15 hours every day of the week," said Rahul Jaiswal, who has worked as an auto rickshaw driver for more than 20 years.
The sides of auto rickshaws are open to the elements, making drivers vulnerable to the effects of smog.
"We have been hearing in the news that breathing this air is like smoking 20 cigarettes so imagine what it's like for us," Jaiswal added.
According to Jaiswal, there has been a clear deterioration in the city's air quality in recent years. "This has been happening for the last five years, especially during the winter. The difference is huge."
Rohtas Singh, a Delhi Traffic Police officer, has also seen the air quality worsen. However, the impact on his health hasn't been as detrimental because he is provided with a special pollution mask.
"The mask provides relief. I have no health problems. I don't really have breathing troubles as I wear the mask in the mornings and evenings when the pollution is at its worse," said Singh.
Rana also tried using a pollution mask but found it offered him little relief. An effective mask like the one worn by Singh can cost around $20, a price too high for Rana, whose take home pay is equivalent to around $4 day.
Instead, Rana ties a wet handkerchief around his face when driving during times of peak winter pollution.
Delhi's air quality worsens
Air quality measurements provided by air quality monitoring stations track smog levels across the city in real time.
The past week has seen air quality in the city plunge. On Thursday, the air quality index reached levels of 999 in some parts of Delhi, the highest reading available before levels go "off-the-charts."
Those levels are based on the concentration of fine particle matter, known as PM2.5, per cubic meter. The microscopic particles, which are smaller than 2.5 micrometers in diameter, are considered particularly harmful because they are small enough to lodge deep into the lungs and pass into other organs, causing serious health risks.
The World Health Organization considers a PM2.5 density below 25 micrograms to be safe.
Last month, the country's Supreme Court banned the sale of most firecrackers amid concerns that their use during the annual celebrations would again send pollution levels soaring.
The polluting pyrotechnics aren't the sole reason behind the toxic smog. In fact, aside from periods of intense use like Diwali, they don't have much of an impact.
Delhi's pollution is driven by more systemic problems such as poor infrastructure and clogged roads, aggravated by the city's unfortunate geography.
The landlocked city sits in a natural bowl and is surrounded by industrial and agricultural hubs.
Without the coastal breeze of cities such as Mumbai and Chennai, much of the pollution settles.
In addition, every year, farmers across fertile neighboring states set fire to their fields to clear them for the next season.
Known as stubble burning, millions of tons of crop residue are set alight at a time of year that typically coincides with Diwali.
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