On a frigid January morning in Ulaanbaatar, the air is thick enough to taste. In the ger districts that ring the capital, families wake to the acrid smell of burning coal. The source is not a distant power plant but the small metal stove in the middle of their felt-walled home. For children under five, who spend most of their time indoors, this is the air they breathe for eight months of the year. Mongolia has some of the world's highest childhood asthma rates, and a growing body of evidence points to the smoke that seeps through every seam of a ger. But not all researchers agree on the link, and the debate has real consequences for how the country spends its limited health budget.

The Ger District Air That Children Breathe

Ulaanbaatar's ger districts are home to an estimated 800,000 people, many of whom migrated from rural areas after the collapse of the Soviet Union. The traditional felt tents, or gers, are designed for nomadic herders, not for permanent urban living. They lack insulation, and their roofs are often little more than felt and canvas. In winter, temperatures drop to -30°C, and families rely on coal-fired stoves for both heat and cooking.

The result is a seasonal air pollution crisis. During the coldest months, outdoor PM2.5 levels in the ger districts regularly exceed 1,000 µg/m³ — more than 60 times the World Health Organization's annual guideline of 15 µg/m³. But the most dangerous exposure happens indoors. A 2019 study in Environment International measured indoor PM2.5 concentrations in gers during winter and found averages between 200 and 400 µg/m³, with peaks much higher. The same study reported that 40% of children in ger districts had bronchitic symptoms — cough and phlegm for three months or more — compared to 15% in apartment buildings, and indoor PM2.5 was the strongest predictor.

Children under five spend an estimated 20 or more hours per day inside these homes. Their developing lungs are especially vulnerable. Asthma prevalence in Mongolian children is now estimated at 15–20%, among the highest in the world. But the numbers are not straightforward. Adult asthma rates are much lower, around 4%, suggesting that early-life exposure patterns matter. And confounding factors — such as a male smoking rate near 45% — complicate the picture.

The WHO Mongolia office has called for specific monitoring programs, such as the deployment of low-cost PM2.5 sensors in ger districts and a pilot health surveillance system that tracks asthma-related emergency visits in real time. However, the data infrastructure remains patchy. No large-scale randomized intervention has tested whether reducing indoor smoke directly lowers asthma incidence. The question is not just academic: it shapes how the government allocates resources between treatment and prevention.

Why Experts Disagree on the Asthma Link

Among pulmonologists in Ulaanbaatar, there is a split. Some point directly to coal smoke as the cause of the asthma epidemic. They note that the rise in asthma rates in the 2000s coincided with a surge in coal use in ger districts, as rural migrants poured into the city. Others argue that indoor biomass smoke — from dung and wood burned alongside coal — may be the more important driver, and that the focus on coal distracts from a broader housing problem.

Pediatrician Dr. Enkhtuya S., who works at the National Center for Maternal and Child Health, says she sees wheezing and respiratory distress in children every winter. But she cautions that few cases are confirmed by spirometry. “We diagnose asthma clinically, but without objective lung function testing, we may be overdiagnosing,” she told me. “The symptoms could be from recurrent respiratory infections triggered by smoke, not asthma per se.”

Epidemiologist Dr. Ganbaatar O. of the Mongolian National University of Medical Sciences disagrees. He points to cohort data showing a dose-response relationship between PM2.5 exposure and asthma symptoms. “The evidence is consistent,” he says. “Children in the highest exposure quartile have roughly twice the odds of wheeze compared to the lowest.” But even he acknowledges that observational studies cannot prove causation, and that no trial has randomly assigned families to cleaner air.

The Clean Stove Program That Fell Short

Mongolia's clean stove program was one of the most ambitious in the world. Starting in 2012, the government subsidized improved stoves that burned coal more efficiently, aiming to reduce both outdoor and indoor pollution. Early results were promising: a 2015 evaluation found that the new stoves reduced indoor PM2.5 by about 25% compared to traditional stoves. But by 2020, a follow-up study found that many of the gains had disappeared.

The reasons were multiple. The stoves themselves degraded over time; the metal rusted, the seals broke, and the fans (in models that had them) failed. Users often could not afford replacement parts. And the improved stoves required a more expensive type of processed coal, which many families could not sustain. “Once the subsidy ended, people went back to buying raw lignite, which is cheaper but dirtier,” said a 2021 World Bank report titled Mongolia: Clean Stove Program Evaluation — Lessons Learned.

The program also did not address the housing itself. Even with a cleaner stove, a ger's felt walls and roof let smoke escape into the living space. A study by the Mongolian National University found that indoor PM2.5 in gers with improved stoves was still above 200 µg/m³ on average — well above the WHO guideline. “You can't stove your way out of this problem if the house is a tent,” one researcher told me.

An alternative is to extend the district heating network, which serves apartment buildings, into ger areas. But the cost is high — roughly $2,000 per household, according to a 2022 feasibility study — and the city's infrastructure is already strained. As of late 2024, only about 20% of ger district homes were connected to district heating. The rest rely on coal, and will for the foreseeable future.

The disagreement over the primary cause of asthma has direct policy implications. If coal smoke is the main culprit, then switching to cleaner stoves or fuels should be the priority. If biomass or poor housing conditions are more important, then interventions need to address insulation, ventilation, and fuel type together. The World Bank evaluation highlighted that “behavioral and maintenance failures” limited the program's impact, but it also noted that the stoves alone could not overcome the structural deficiencies of the housing.

Inside a Bedsit: Where Smoke Meets Lung

To understand the exposure, it helps to visit a ger. I accompanied a public-health researcher to a home in the Bayanzurkh district one afternoon in February. The family of five lived in a single room, about 20 square meters. In the center was a metal stove, burning a mix of coal and dried dung. There was no chimney; the smoke rose to the roof and seeped through the felt. The mother, who asked not to be named, said her youngest child, age three, had been coughing for two months.

Indoor air measurements taken during our visit showed PM2.5 hovering around 350 µg/m³. The researcher, Dr. Tserendulam B., explained that this was typical. “The worst part is that the smoke accumulates overnight, when the stove is banked low and the family sleeps,” she said. “Children are exposed for 10 to 12 hours straight.”

The lack of longitudinal data is a major gap. Dr. Tserendulam and her colleagues have proposed a randomized trial that would insulate gers and install better stoves in one group, then follow children for three years. “We need a trial that randomizes insulation upgrades, not stoves,” she said. “But funding is a problem. The government spends about 4% of GDP on health, and most of that goes to hospitals, not prevention.”

To see the scale of the problem, consider the history of the ger districts. After the Soviet collapse in 1991, Ulaanbaatar's population doubled within a decade as herders lost state support and moved to the city. The city's formal housing sector could not keep pace, so newcomers erected gers on the outskirts. By 2000, roughly 40% of the city's population lived in these informal settlements. The districts grew without planning: no paved roads, no sewer lines, no district heating. Coal became the only affordable fuel, and its use soared. Asthma rates among children rose in parallel, from an estimated 5% in the late 1990s to 15–20% by 2010. The correlation is striking, but causation remains debated.

What the Data Actually Show

Mongolia's asthma statistics are striking, but they require careful interpretation. The Global Asthma Network estimates that childhood asthma prevalence in Mongolia is 15–20%, placing it among the top five countries worldwide. Yet adult asthma prevalence is only about 4%, which is close to the global average. This discrepancy suggests that something about childhood exposure in Mongolia is uniquely harmful, or that diagnostic practices differ by age.

COPD mortality in Mongolia is roughly 50 per 100,000, compared to a global average of 40. That gap may be driven by smoking, which is common among men, but also by early-life lung damage from smoke exposure. A 2018 study found that Mongolian adults who lived in gers as children had lower lung function than those who grew up in apartments, even after adjusting for smoking.

There is no clear temporal trend: asthma rates rose sharply during the 2000s, then plateaued after 2010. That pattern mirrors the growth of the ger districts themselves, which expanded rapidly in the early 2000s and then stabilized. But it also coincides with improvements in asthma diagnosis and awareness. “Some of the increase may be real, but some is probably due to better detection,” Dr. Ganbaatar acknowledged.

The most rigorous study to date, a 2020 meta-analysis of 12 Mongolian studies, found a consistent association between indoor PM2.5 and childhood wheeze, but the effect size varied widely. The authors concluded that “the evidence is suggestive but not conclusive,” and called for a randomized trial. That trial has not happened.

The Clinical Dilemma: Treat or Prevent?

For clinicians, the uncertainty creates a dilemma. Inhaled corticosteroids and bronchodilators can control asthma symptoms, but they are expensive. A monthly supply of a commonly used inhaler costs about $15 in Mongolia — a significant sum for a family earning $200 per month. Many families cannot afford it, or they ration the medication, using it only when symptoms are severe.

Dr. Enkhtuya says she often prescribes inhalers but knows that many patients will not fill the prescription. “I tell them to keep the child indoors on high-pollution days, but indoors is not clean either,” she said. “The real solution is to fix the housing, but that's not my job as a doctor.”

Prevention, in theory, is more cost-effective. A 2019 health-economic analysis estimated that insulating gers and providing clean stoves would cost about $1,500 per household and could reduce asthma-related hospitalizations by 30%. But the analysis relied on assumptions from observational studies, not trial data. “We don't know if it would actually work,” said Dr. Tserendulam. “We need to test it.”

The WHO Mongolia office has advocated for a concrete integrated approach: a pilot project in the Chingeltei district that combines low-cost PM2.5 sensors, a mobile health alert system, and subsidized stove upgrades. This project is still in the planning stage, with funding sought from international donors. But progress is slow. The country's health budget is tight, and most funding goes to curative care. Preventive interventions, especially those that cross sectors — health, energy, housing — are hard to fund and evaluate.

Three Things That Might Actually Work

Despite the uncertainties, a few interventions have shown promise. The first is expanding district heating to ger areas. A pilot project in the Songino Khairkhan district connected 500 homes to the central grid and reduced indoor PM2.5 by 80%. The cost was about $2,000 per household, but the long-term health benefits could offset that. A 2023 cost-benefit analysis estimated that every dollar spent on district heating returns roughly $3 in reduced health costs. However, the main drawback is the high upfront capital investment and the need to extend the existing network, which is already at capacity in some areas.

The second option is switching to electric heat pumps, which produce no indoor emissions. A small pilot in Ulaanbaatar, funded by the Asian Development Bank, equipped 100 gers with heat pumps and solar panels. Indoor PM2.5 dropped to near zero, but the upfront cost was high — about $3,000 per household — and the pumps struggled in extreme cold, with efficiency dropping when temperatures fell below -20°C. The technology is improving, but it is not yet ready for widespread use, and the electricity grid would need upgrades to handle the additional load.

A lower-tech option is to mandate chimney caps and roof sealing. Many gers lack proper chimneys; smoke simply leaks through the roof felt. Installing a metal chimney with a cap costs about $50 and can reduce indoor PM2.5 by 30–50%, according to a 2022 study. Sealing the roof felt with a layer of plastic and mud costs even less. These measures are not glamorous, but they are cheap and could be implemented at scale. The limitation is that they require regular maintenance and do not address the source of pollution — the stove itself — so indoor air may still be unhealthy, especially if the stove is used continuously.

None of these interventions have been rigorously tested in a controlled trial with asthma as the primary outcome. The closest is a 2023 study that used a mobile app to deliver real-time indoor PM2.5 alerts to families in Ulaanbaatar. The app prompted families to open windows or use masks, but adherence was low, and the study did not measure health outcomes. “We have plausible ideas, but we don't have proof,” Dr. Tserendulam said. “That is the uncomfortable place we are in.”

The gap between what the evidence suggests and what policy requires is wide. On one hand, the health toll on children is visible and urgent: every winter, emergency rooms fill with wheezing toddlers, and families burn coal in the same room where they sleep. On the other hand, the interventions that might help — district heating, insulation, heat pumps — are expensive, unproven in trials, or both. The clean stove program showed that even well-funded efforts can falter when they ignore the broader housing context. The challenge is not just technical but institutional: health, energy, and housing ministries rarely coordinate, and the health budget is too small to fund large-scale housing upgrades. Until a randomized trial provides clear evidence, the debate over causation will continue, and children will keep breathing smoke.