New Delhi has been engulfed in a dense blanket of smog – a mix of fog, car exhaust and manufacturing soot – in recent days. A look at what prompted skyrocketing levels of pollution and tips on how to get through it.

1 What causes the smog?

Delhiites are no strangers to smog. As temperatures dip each year, exhaust fumes from the capital’s 7.2 million vehicles combine with construction dust, soot from the mass-burning of agricultural waste in the neighboring states of Punjab and Haryana, and emissions from factories, to produce a lethal mix, Vivek Chattopadhyay, an air pollution analyst at New Delhi-based Centre for Science and Environment, said. For the landlocked northern Indian metropolis, the problem is worsened by the absence of coastal breeze, which helps steer away polluted air.

Car emissions account for around 75% of the capital’s pollution, CSE estimates. Despite attempts to upgrade infrastructure, the number of people using public transportation has actually gone down over the years, according to a government report.

2 Is it really that bad?

Air Pollution is typically judged by “PM 10” and “PM 2.5” levels in the atmosphere. PM 10 levels measure pollutants with a diameter of 10 microns or less, while PM 2.5 measure pollutants with a diameter of 2.5 microns or less.

By U.S. standards, for both measurements, a level of more than 201 is classified as “very unhealthy,” and levels higher than 301 are considered “hazardous” to health. Pollution levels above this, “would trigger health warnings of emergency conditions” according to a U.S. government body, which warned that in such a scenario “everyone should avoid any outdoor exertion.”

Over the last few days, the air quality index for PM 10 and PM 2.5 in New Delhi has ranged from 400 to 500, according to data collected by India’s Ministry of Earth Sciences. Early Thursday, the average air quality index for PM 10 was 410 and for PM 2.5 was 417, both levels described by the ministry “very unhealthy.”

In 2010, the capital’s PM 10 averaged 249, according to data from India’s Environment Ministry. That made it India’s most polluted city.

3 How does this affect me?

If you’re catching a flight out of New Delhi this week, particularly if you’re setting off in the morning, there’s a chance you could be in for a delay or even a cancellation. On Monday, when the dense blanket of smog enveloped the Indian capital, at least 140 flights were either cancelled or delayed, according to an airport spokesman. On Tuesday, 19 flights were cancelled, while on Wednesday, another 40 were delayed. Several trains in the city have also been stalled or cancelled this week, local media reported.

Doctors said weather conditions have worsened the condition of patients suffering respiratory ailments such as bronchitis and asthma. Manoj Goel, who heads the pulmonology department at Delhi’s Heart and Lung Institute, says he’s attended to dozens of patients in the last few days. He estimates that is a 25% increase from the number of patients he attended to when winters set in this time last year.

4 What can I do to get through it?

Mr. Goel suggests wearing surgical masks to block polluted particles, but cautions that they can’t always filter poisonous gases such as nitrogen dioxide, carbon monoxide and ozone, which are all on the rise in the Indian capital. His advice: “Step out of the house only when the smog subsides.” He also warns against outdoor exercise — at least until the smog clears. Exercising accelerates the flow of air pollutants into your lungs and to the rest of your body, increasing the chances of respiratory ailments.

For a long-term solution, follow the footsteps of India’s Oil Minister: hop onto a public bus or the subway at least once a week.

5 What next?

via 5 Things to Know About Delhi’s Air Pollution – Five Things – WSJ.