Measurement report: Unexpected high volatile organic compounds emission from vehicles on the Tibetan Plateau

Abstract. Vehicular emissions significantly impact atmospheric composition, yet their behavior in high-altitude environments remains poorly understood. Here, we present a comprehensive investigation of vehicular emissions conducted across ten tunnels on the Tibetan Plateau, encompassing nearly 3000 m of altitudinal variation. Our findings reveal that total emission factors of volatile organic compounds (VOCs) increase with altitude, driven primarily by a pronounced rise in evaporative emissions. Source apportionment indicates that evaporative emissions contribute 67 % of the total VOCs, markedly outweighing the 24 % from tailpipe exhaust, a pattern that diverges from those observed at lower altitudes, where tailpipe emissions dominate. We identify low atmospheric pressure as the key factor enhancing evaporative VOC release at high altitudes. This study offers critical new insights into the mechanisms of vehicular emissions in plateau regions, underscoring the necessity of accounting for specific environmental conditions and fuel evaporation when formulating emission control strategies for high-altitude settings.