At one of the busiest intersections in Kathmandu, business is good for 64-year-old Nucche Khadka. He says he’s been working this spot for 40 years, selling crackers, candy and cigarettes. A steady stream of customers buy cigarette boxes decorated with grotesque pictures of cancerous lungs, meant to warn customers of the danger of their contents.

But the air they are breathing may not be much better than the cigarette smoke.

Air quality monitors installed in August are revealing what residents have long suspected: Kathmandu has some of the most toxic air on Earth. In the dead of winter, pollution was at its peak, with the Air Quality Index daily soaring above 200.

To make matters worse, most of the streets have been torn up to lay pipe for a water expansion project, sending dust into the air. Like many of the city’s residents, Khadka wears a black cloth mask, but it doesn’t stop the most harmful particles, which are smaller than 2.5 microns (pm) wide.

He complains he has a cough and sore throat that keeps returning.

“It’s too expensive to go to the doctor, I take medicine from the pharmacy,” he says.

Nepal’s air quality is the fourth-worst in the world, according to Yale’s 2016 Environmental Performance Index. The nation’s capital Kathmandu is also one of the fastest-growing metropolitan areas in South Asia and contains a burgeoning middle class, who’ve funded a boom in construction and auto sales. Until the government recently slowed the rate of lending, residents could get an auto loan with only a 10 percent down payment.

But people here are becoming increasingly aware and concerned with the air pollution. Student protests and a constant stream of articles in local newspapers are pressuring the government to clean up the air. In March, the police began enforcing a law made two years ago that outlaws public transportation vehicles more than 20 years old.

Sabin Pradhan, the deputy superintendent for the Metropolitan Traffic Police Division, said last month they issued tickets to 1,000 overage vehicles in just 10 days.

Langtang valley, north of Kathmandu, Nepal. Glaciers there have been receding. Credit: Stephen Groves/PRI

“In Nepal, if we want to implement something that is forward-thinking, then there is a lot of resistance. But once we catch the vehicles, they’ve been cooperative,” he said.

The pollution comes from many sources besides vehicles, though. Some of the worst air in Nepal is not in Kathmandu, but in the southern plains, where brush fires, brick kilns and cooking stoves produce a haze of smoke.

The pollution could have far-reaching consequences as it floats north into the Himalayas. Smoke from fires and emissions from vehicles produce soot containing black carbon. Black carbon absorbs lots of solar energy. It settles on glaciers and snow, and its dark color causes the snow and ice to absorb more of the sun’s radiation. It also warms up the air, changing rainfall patterns.

For the mountains that are called the “water towers of Asia,” this could have serious impacts. Over a billion people depend on the monsoon rains and snow melt of the Himalayas for their source of water.

Last week, an Indian court granted “living entity” status to the Gangotri and Yamunotri glaciers, which feed the Hindu holy rivers Ganga and Yamuna. The judges said the glaciers are shrinking at an alarming rate. The Ganga river is also fed by glaciers in the Nepali part of the Himalayas.

Researchers are still studying how much black carbon itself causes glacier melt, and how much is caused by rising global temperatures. So far, scientists haven’t been able to pinpoint to what extent the glaciers have melted since there’s a lack of historical data and the glaciers themselves can be difficult and expensive to reach. However, a recent paper in The Cryosphere suggested that glaciers in the Everest region could lose 70 to 99 percent of their mass by 2100 due to climate change.

Greenhouse gases are the leading cause of the warming atmosphere, but black carbon is also a major contributor to shrinking glaciers, especially when the sources of the soot are so close to them.

“The closer you are to a glacier, of course, the greater the impact on that glacier,” said Dr. Arnico Panday, a researcher at Nepal’s International Centre for Integrated Mountain Development.

Kathmandu is only 43 miles away from the closest glaciers, and its black carbon is within striking distance of thousands more.

Stephen Groves reported from Kathmandu, Nepal.