Key Takeaways & Executive Findings
- •• • TVOCs concentrations at the two sites were 60.04×10⁻⁹ and 83.28×10⁻⁹, with OVOCs dominating (55.14% and 62.91%), indicating that oxygenated species are the primary VOC fraction in high-altitude counties, which is critical for designing targeted control strategies. • • Industrial sources contributed the largest share (43.2%) to VOC emissions, but site-specific differences (solvent use 30.7% at Government site vs. domestic sources 27.6% at Middle School site) highlight the need for localized emission inventories and tailored abatement measures. • • OFP values were 258.84×10⁻⁹ and 378.04×10⁻⁹ at the two sites, with alkenes and OVOCs as the main contributors, underscoring that these reactive species should be prioritized in ozone mitigation efforts. • • EKMA curves confirmed that the region is VOC-limited, meaning that reducing VOC emissions will effectively lower ozone formation, validating the focus on VOC control in this area.
Abstract
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.
1. Introduction
The Guanzhong Plain, a region with severe ozone pollution, has seen increasing attention on controlling volatile organic compounds (VOCs) as key precursors. However, most studies have focused on urban or regional scales, leaving a gap in understanding VOC pollution at the county level, particularly in high-altitude areas where atmospheric chemistry may differ. Existing commercial monitoring networks often lack the spatial resolution to capture local emission patterns, hindering the development of effective ozone control strategies for smaller administrative units.
This study addresses this bottleneck by conducting continuous monitoring of 53 VOC species at two sites in Changwu County, a high-altitude (1200 m) county in the Guanzhong Plain. By analyzing the spatiotemporal characteristics, ozone formation potential, and source apportionment using PMF, the research provides a detailed picture of VOC pollution in a typical high-altitude county. The findings reveal that OVOCs dominate, and industrial sources are the largest contributor, but with significant site-specific variations. These insights are crucial for designing targeted emission reduction policies, offering a replicable framework for ozone pollution control in similar county-level regions.
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MO Xinyu, LI Dan, SHEN Zhenxing, ZHENG Honghao, YE Xinpeng, SUN Jian, ZHANG Bin, YANG Liu, XU Hongmei (2026). Characteristics of Volatile Organic Compounds in High-Altitude Counties of the Guanzhong Plain in Summer: Implications for Ozone Pollution Prevention and Control. Environmental Chemistry. https://doi.org/10.7524/j.issn.0254-6108.2025010802
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Frequently Asked Questions
What are the dominant VOC species and their concentrations at the two monitoring sites, and how do they influence ozone formation?
At the Government and Middle School sites, TVOCs averaged 60.04×10⁻⁹ and 83.28×10⁻⁹, respectively. OVOCs were the dominant group, accounting for 55.14% and 62.91% of TVOCs. The OFP values were 258.84×10⁻⁹ and 378.04×10⁻⁹, with alkenes and OVOCs being the primary contributors, indicating that these reactive species are key drivers of ozone formation in this region.
How does the source apportionment differ between the two sites, and what are the implications for local emission control?
Industrial sources contributed the most overall (43.2%), but the Government site was dominated 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%). This suggests that control measures should be tailored to the specific emission profiles of each area, such as regulating solvent use near government areas and addressing domestic emissions near residential or school zones.
What is the ozone sensitivity regime in Changwu County, and how does it affect the effectiveness of VOC control?
EKMA curves indicated that Changwu County is in a VOC-limited regime during the observation period. This means that ozone formation is more sensitive to changes in VOC concentrations than NOx, so reducing VOC emissions will be more effective in mitigating ozone pollution. This validates the focus on VOC control strategies in this region.
What are the main sources of the OFP, and how can they be targeted for ozone mitigation?
The OFP at both sites was primarily contributed by alkenes and OVOCs, which mainly originate from industrial emissions, solvent use, and biogenic sources. To reduce ozone formation, control efforts should prioritize reducing emissions from industrial processes, solvent usage, and managing biogenic VOC sources, such as vegetation, if feasible.
How do the VOC concentrations and source profiles in this high-altitude county compare to those in urban areas of the Guanzhong Plain?
While direct comparisons are not provided in the abstract, the study highlights that OVOCs dominate in this high-altitude county, which may differ from urban areas where alkanes or aromatics might be more prevalent. The source apportionment shows a significant industrial contribution (43.2%), which is consistent with regional industrial activities, but site-specific differences emphasize the need for localized data to inform effective ozone control policies.
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