Morning in Delhi, the world’s most polluted megacity: the alarm erupts, the coffee boils, and I look out the window. Ominous clouds of vapor have erased the lime and jamun trees in the park across the way. I can barely see across the street and, beyond the curb, the world vanishes into mist.

“The air is really, really horrible today,” I text my friend Medha, adding a frowning face. This is a tacit cancellation of our morning walk in Lodi Gardens.

“Are you sending the kids to school?” she replies.

Oh, really, it’s that bad? I go online to check the air-quality index. The latest U.S. Embassy measurement shows almost six hundred parts per million of the deadly particulate matter 2.5, which is tiny enough to enter the bloodstream through the lungs. The measurement is beyond the extremes of “hazardous,” the direst classification. “Good” air contains fifty parts per million or lower. A mere “unhealthy” is between a hundred and fifty-one and two hundred.

Air pollution throttles the Indian capital during the winter weeks between November and January. In this smoggy season, the air quality can fluctuate by the day and even by the hour; other times, the toxic haze sits stubbornly over the capital for days. The construction dust, industrial smog, and vehicle emissions are constant. But the air is also dramatically affected by wind speed and direction, temperature inversions, torrents of thick smoke from farmers burning fields because it’s the cheapest and fastest way to prepare the soil for planting, and fireworks unleashed to celebrate Diwali.

I peck a reply back to Medha: Yes, I’ll send our eldest son to school. There’s no point in keeping the six-year-old home. His school, which educates the children of wealthy Indians and foreigners from around the world, is one of only a handful in Delhi with built-in, industrial-grade air-filtration systems. His classroom contains some of the cleanest air in town.

Still, I know some of his friends will be absent. Raising children in poisonous air is crazy-making, and once you start worrying it’s hard to stop. What if the kids forget to close the classroom door? How about crossing the grounds to lunch, the sports hall, the auditorium? You start obsessing about every breath, and soon you find yourself imprisoning your child at home while praying for a good, strong wind.

There are few precedents for the dystopian days my family is about to have. Delhi’s recent pollution spikes recall the “Great Smog,” which is believed to have killed as many as twelve thousand people when it smothered London, in 1952. Since the nineteen-sixties, a series of Clean Air Acts has shielded Americans from heavy smog, although Donald Trump has pledged to revive the coal industry and roll back environmental regulation. Meanwhile, toxic air is a stubborn hardship of contemporary life in Africa, Asia, and the Middle East, as an unprecedented global migration drains workers from impoverished agricultural lands into overcrowded and energy-famished cities. For many millions of people, breathing is a necessary hazard.

Here in Delhi, it’s a cliché of our coughing metropolis that smog is the great social leveller. The bad air affects rich and poor alike, the chattering class likes to claim at cocktail parties and in editorial headlines.

But it’s simply not true. This is the dirtiest secret about dirty air: the wealthy buy their way around it. Slowly, I’ve acclimated to the idea that a small handful of residents can breathe safely, and the rest cannot.

This segregated reality is woven through our family life. State-of-the-art Swedish purifiers churn around the clock in our rooms; a portable purifier cleans the air in our car. Air-filtering masks protect our lungs as we pass from building to car to building. A Tae Kwon Do instructor visits our living room so our children and their friends get some exercise without braving the outdoors.

Speaking of the kids, they’ll have to get up soon. Angie, our nanny, walks across the back yard from the “servants’ quarter” and lets herself into the living room, unwrapping a scarf from her head. In the kitchen, she slices apple and papaya while I scramble eggs.

Angie is distracted and upset. A guard she’d befriended at a previous household died the night before; his wife called Angie crying. The man had asthma, but his job kept him outside. He coughed and gasped for hours, and finally he died.

“He was a nice man,” Angie tells me. “I feel pity.”

I’m not sure what this story means in medical terms. He had a heart attack? His throat swelled to block his airways? Can that happen? People who downplay the harmful effects of pollution (including an outspoken member of the Trump E.P.A. transition team, who took to Twitter to taunt Indians for fussing over the smog) often claim that it doesn’t directly cause death—just lung damage and cancer and heart attacks. The Indian Supreme Court has said that three thousand people die every year from pollution in Delhi; environmental advocates place that figure as high as thirty thousand. These statistics float through the news cycles, alongside photographs of overcrowded emergency rooms and face masks; one study follows the next, and the numbers seldom match.

Now I’m prodding the eggs with a spatula, wondering whether my six-year-old’s soccer practice will be cancelled and whether it’s physically possible to cough to death. I make a mental note to ask the kids’ pediatrician next time I see him.

“Was it always like this?” I ask Angie.

“Always,” she says. “But we thought it was just fog.” Until recently, the smog was routinely dismissed as fog, and doctors advised patients to go outside and develop immunity.

My husband and kids get up and we eat a gloomy breakfast. Thick, charcoal-colored brume presses on the dining-room windows. One of our air purifiers— the one in the playroom—has stopped working. This is an ill-timed malfunction. I remember the difficulty of running down company representatives last year, when a similar pollution spike provoked a citywide run on masks and filters.

Our younger son’s preschool is a small, family-run operation. Its lone purifier is no match for these pollution levels, so the staff sends an e-mail cancelling school. Hearing the news, our son weeps bitterly. It was his turn for show-and-tell.

I flash back to the snow days of my own childhood, in Connecticut: news on the radio, drifting back to sleep, and waking to the rasp of metal shovels on ice, afternoons spent sledding down hills of pine. These memories strike me, now, with their unbelievable cleanliness. We slurped on fresh-fallen snow; drew hard, pure air like knives up our nostrils.

“I don’t want to wear the mask! I hate the mask!” my elder son hollers at the front door, dropping his backpack in protest.

“You have to wear the mask, or you can’t go to school.”

“Fine, then I don’t want to go to school,” he scowls, although he loves school.

“You have to go to school.”

His cause is lost from the start, but he protests until, at last, the straps have been carefully hooked over his ears.

I walk him to the car. I do not wear a mask. The pollution season crept up on us suddenly this year, and we only purchased the kids’ masks in advance. I remind myself to drop by the city’s trendiest market, where a new shop sells reusable, printed cotton masks for about thirty dollars each. In the driveway, I smell smoke and chemicals and shallow my breathing. I am sipping at the atmosphere, taking in minimum air. When I walk too fast or breathe too deeply I see stars, tiny chips of light that flash at the edges of my vision. I am careful to chat cheerfully with my son.