关中平原高海拔区县夏季 VOCs 污染特征及臭氧污染防控启示

The issue of ozone (O₃) pollution in the Guanzhong Plain region is particularly prominent, making the control of its precursors, especially volatile organic compounds (VOCs), especially crucial. Currently, research focusing on the pollution characteristics of VOCs at county levels is rarely reported. To examine the characteristics of VOC pollution and its sources during summer in high-altitude towns of the Guanzhong Plain, two monitoring sites in Changwu County, Xianyang City (elevation 1200 m) were selected for continuous monitoring of 53 typical VOC species. This study analyzed spatial-temporal variations of ambient VOCs and their ozone formation potential (OFP). Additionally, source apportionment of VOCs was conducted using the Positive Matrix Factorization (PMF) model. The results revealed that the average concentrations of total VOCs (TVOCs) at the two monitoring sites —the Government Office of Changwu and Changwu Middle School were 60.04×10⁻⁹ and 83.28×10⁻⁹, respectively. OVOCs (oxygenated volatile organic compounds) were the dominant components, accounting for 55.14% and 62.91% of the TVOCs at the Government and Middle School sites, respectively, followed by alkenes, aromatic hydrocarbons, and halogenated hydrocarbons. VOC emissions in Changwu County predominantly originated from industrial sources (averagely 43.2%). However, the two monitoring sites exhibited slight differences in emission sources: the Government site was primarily influenced by solvent emissions (30.7%) and motor vehicle emissions (19.1%), while the Middle School site was predominantly affected by domestic sources (27.6%) and motor vehicle emissions (20.0%). Moreover, the average OFP values at the Government and Middle School sites were 258.84×10⁻⁹ and 378.04×10⁻⁹, respectively. The primary contributing components were alkenes and OVOCs, mainly originating from industrial emissions, solvent usage, and biogenic source emissions. Empirical Kinetic Modeling Approach (EKMA) curve shows that O₃ formation was VOCs-limited in Changwu County, proving the effectiveness of controlling VOCs emissions for ozone pollution management. The results of this study suggest that ozone control measures in Changwu County should prioritize VOCs emissions from industrial emissions, solvent usage and household emissions. These findings not only provide scientific guidance for local ozone control, but also offer an effective paradigm for the precise prevention and control of ozone pollution at county levels of the Guanzhong Plain.