First measurement report for volatile organic compounds characteristics during winter in Ulaanbaatar, Mongolia

In this study, 34 volatile organic compounds (VOCs) were analyzed using an online VOCs instrument at 30-min intervals from November 16 to November 23, 2023, in Ulaanbaatar (UB), the capital of Mongolia for the first time. The average concentration of the 34 VOCs was 13.0 ± 11.1 ppb, with the top 10 compounds, such as benzene, toluene, ethylbenzene, and xylenes (BTEX), constituting 80 % of the total. The concentrations of n-hexane, n-heptane, and undecane tended to increase significantly during high-concentration episode period (HEP). Compared to other studies, BTEX concentration levels in UB were higher than those in Seoul and Beijing, but lower than in Southeast Asian cities. Positive matrix factorization (PMF) identified four VOCs sources: vehicle exhaust (33.8 %), industrial/coal combustion (25.3 %), secondary formation precursors (21.3 %), and solvent usage (19.6 %). Vehicle exhaust and industrial/coal combustion sources increased during rush hours and were strongly correlated with nitrogen oxides. During HEP, stagnant air mass led to increased contributions from vehicle exhaust and industrial/coal combustion sources, indicating a significant local impact. Solvent usage appeared to be influenced by building materials and exterior painting which increased with high relative humidity. Secondary formation precursors increased in concentration during daytime and were highly correlated with ozone. Among the measured compounds, benzene was assessed for lifetime health risk, showing that adults with the prolonged exposure exhibited higher risk than infants and children. However, during HEP, children were also at increased risk, despite their shorter exposure duration. Based on the concentration levels of VOCs and the associated health risks, the results highlight that the need for a policy on ambient VOCs management in UB, with a particular focus on local source management.