Indoor environments: Evaluating air quality in Ulaanbaatar's traditional gers

Ulaanbaatar (capital of Mongolia) is struggling with serious air pollution. In the so-called ger districts of the city, approximately 60 % of the population live in traditional Mongolian dwellings called gers, mostly relying on coal for winter heating. This study investigates PAH concentrations and associated health risks in 6 gers situated in the Songinokhairkhan district. The majority of the gers (5 out of 6) were characterized by the dominance of higher molecular weight, 5-and 6-ring-PAHs. In two of the sampled gers (G3 and 4), total PAHs concentrations were extremely high, reaching 38700 μg/g and 36200 μg/g. Using a Gradient Boosting Machine algorithm, we identified key PAHs-pyrene, benzanthracene, and phenanthrene-as primary indicators distinguishing gers with high (G2-4) versus low (Gers1, 5, and 6) air PAH levels. Incremental Lifetime Cancer Risk (ILCR) assessments for both adults and children revealed that Gers 3 and 4 present the highest PAH-related cancer risks, with benzo(a)pyrene contributing substantially. Principal Component Analysis (PCA) further underscored distinct PAH profiles across the sites, and a dissimilarity matrix identified significant variation, particularly between Gers 4 and 5. Additionally, decision tree analysis highlighted Ger 4 as having the most distinct PAH characteristics. The combination of high altitudes, cold continental climate, and reliance on combustion within these gers emphasizes the potential for persistent pollutant buildup, particularly during winter. Our results underscore the urgent need for interventions in Mongolia and similar Central Asian regions, where indoor air quality is severely affected by traditional heating practices, contributing to elevated long-term health risks.