Asian Monsoon and Local Valley Wind Caused Transport of Volatile Organic Compounds Episode Across Qinling Mountain in China

Transport of volatile organic compounds (VOCs) and their oxidation products enhances ozone (O₃) levels in the downwind areas. Qinling Mountain, with high altitude, affects the climate and air quality in China, but its impacts on VOCs transport and regional O₃ pollution are poorly understood. The present study measured ambient VOCs at a high-altitude site in Qinling Mountain in China in summer and winter in 2020, and investigated how the mountain influenced the regional transport of VOCs and O₃. Transport of VOCs (formaldehyde up to 5 ppbv) across Qinling Mountain was observed, which caused rapid increase of O₃ at night (80–152 ppbv) at the mountain top. In August, southeasterly air masses from surrounding areas were the main sources of oxygenated VOCs, while nonmethane hydrocarbons originated mainly from the Guanzhong Basin (GZB) north of the mountain. High loading of tropospheric formaldehyde was distributed on the pathway of the southeasterly air mass, which verified the transport of VOCs across Qinling Mountain. In December, westerly air masses passing through GZB contributed most to the ambient VOCs. Asian monsoon and local valley wind together drove the accumulation of O₃ and VOCs on the mountain top, which exacerbated the O₃ pollution in the adjacent areas. This study revealed the transport of O₃ and VOCs across Qinling Mountain and highlighted the need for regional collaborative control of air quality in Northwest China.