Characteristics of Volatile Organic Compounds in High-Altitude Counties of the Guanzhong Plain in Summer: Implications for Ozone Pollution Prevention and Control
Ozone (O3) pollution is a prominent issue in the Guanzhong Plain, necessitating effective control of its precursors, particularly volatile organic compounds (VOCs). However, studies on VOC pollution characteristics at the county level are scarce. To investigate the summer VOC pollution characteristics and sources in high-altitude towns of the Guanzhong Plain, continuous monitoring of 53 typical VOC species was conducted at two sites in Changwu County, Xianyang City (elevation 1200 m). The spatiotemporal variations of ambient VOCs and their ozone formation potential (OFP) were analyzed, and source apportionment was performed using the Positive Matrix Factorization (PMF) model. Results showed that average total VOC (TVOCs) concentrations at the Changwu Government and Changwu Middle School sites were 60.04×10⁻⁹ and 83.28×10⁻⁹, respectively. Oxygenated VOCs (OVOCs) dominated, accounting for 55.14% and 62.91% of TVOCs, followed by alkenes, aromatic hydrocarbons, and halogenated hydrocarbons. Industrial sources contributed the most (43.2%) to VOC emissions in Changwu County, but site-specific differences were observed: the Government site was primarily influenced by solvent use (30.7%) and motor vehicles (19.1%), while the Middle School site was dominated by domestic sources (27.6%) and motor vehicles (20.0%). The average OFP values at the Government and Middle School sites were 258.84×10⁻⁹ and 378.04×10⁻⁹, respectively, with alkenes and OVOCs as the main contributors, originating from industrial emissions, solvent use, and biogenic sources. EKMA curves indicated that Changwu County was in a VOC-limited regime during the observation period, confirming the effectiveness of VOC control for ozone mitigation. These findings provide scientific guidance for local ozone management and offer a paradigm for precise ozone pollution control in county-level regions of the Guanzhong Plain.