生物源和人为源交互作用下秦岭周边地区大气中挥发性有机物的分子特征和环境影响

Molecular characterization and environmental impacts of atmospheric volatile organic compounds in the Qinling Mountains periphery under the interaction of biological and anthropogenic sources

关键词:  秦岭地区  挥发性有机物（VOCs）  高分辨率在线质谱  分子特征  环境影响

Key words:  Qinling Mountains  volatile organic compounds (VOCs)  high-resolution online mass spectrometry  molecular characterization  environmental impact

摘要:

挥发性有机物（VOCs）是二次有机气溶胶（SOA）与臭氧（O₃）的重要前体物，对区域复合污染形成具有重要影响。为阐明生物源和人为源交互作用下秦岭周边地区大气中挥发性有机物的分子特征和环境影响，基于2021年8月1—31日在关中城市群与秦岭森林过渡地带获取的高分辨率在线质谱观测数据，结合后向轨迹聚类方法探究VOCs的浓度水平、分子组成及气团来源，并利用参数化方法进一步分析其二次生成潜势。结果发现，观测期间共识别出987种可分配化学式的VOCs组分；VOCs的平均总浓度为(130.53±0.03) μg/m³，元素组成上，碳氢氧元素组成的VOCs对总VOCs质量浓度贡献最大，占78.1%；挥发性上，以VOC为主，占62.7%。聚类结果显示观测期间气团可分为生物传输源、人为传输源和本地混合源，这3种来源在分子特征上依次具有较高的不饱和度、较大的分子量和较高氧化程度的特征，分别反映出植物排放的萜烯类物质、人为排放的羰基化合物及二次氧化对以上3种来源的影响。环境影响分析表明，秦岭周边地区VOCs受到生物源输送的萜烯类化合物和人为源输送的羰基化合物的影响，具有较高的SOA和O₃生成潜势。研究结果揭示了秦岭周边过渡地带的大气中VOCs的分子特征与环境影响，可为制定生物源和人为源交互作用下的过渡区域的VOCs差异化管控提供科学依据。

Abstract:

Background, aim, and scope Volatile organic compounds (VOCs) are key precursors of secondary organic aerosols (SOA) and ozone (O₃), playing a crucial role in regional complex air pollution. The Qinling Mountains periphery, located at the transition zone between the Guanzhong urban agglomeration and the Qinling Mountains forest, where atmospheric VOCs are jointly influenced by biogenic and anthropogenic sources. However, the molecular characteristics and environmental impacts of VOCs under such source interactions remain unclear, significantly limiting the formulation of effective pollution control strategies. This study aims to investigate the concentration levels, molecular composition, air-mass sources, and secondary formation potentials of atmospheric VOCs in this transition region. Materials and methods Field observations were conducted from 1 to 31 August 2021 at the Qinling Mountains Station of the Chinese Academy of Sciences (34.07°N, 108.35°E; 689 m a. s. l.). A high-resolution proton-transfer-reaction time-of-flight mass spectrometer (VOCUS-LTOF-PTR-MS) was used to measure atmospheric VOCs. Air mass backward trajectories were calculated using the HYSPLIT_4 model with NOAA (National Oceanic and Atmospheric Administration) meteorological data, and cluster analysis was performed with TrajStat v1.2 to identify source regions. The molecular characteristics of VOCs were examined in terms of elemental composition, the number of carbon and oxygen atoms, double bond equivalence (DBE), and volatility. Parameterization methods were further used to evaluate the ozone formation potential (OFP), secondary organic aerosol potential (SOAP), and source reactivity (SR) of VOCs from different sources. Results A total of 987 formula-assigned VOCs were identified during the observation period, with an average total concentration of (130.53±0.03) μg/m³. In terms of elemental composition, VOCs containing carbon, hydrogen, and oxygen (CHO) contributed the largest fraction of the total VOC mass concentration, accounting for 78.1%, indicating high atmospheric oxidation. In terms of volatility, the VOC volatility class dominated the total mass concentration, accounting for 62.7%. Backward trajectory clustering classified the air masses into biogenic transport (42.7%), anthropogenic transport (15.0%), and local mixed (42.3%) sources. Biogenic VOCs showed lower oxidation, smaller molecular weight, and higher DBE values. Anthropogenic VOCs were characterized by large, oxygen-rich molecules. The local mixed source exhibited the highest oxygen content due to the combined influence of both sources. These features reflected the influences of plant-emitted terpenoids, anthropogenic carbonyl compounds, and secondary oxidation processes. In terms of environmental impacts, CHO and VOCs containing carbon and hydrogen (CH) were the dominant contributors to ozone formation potential (OFP) and secondary organic aerosol potential (SOAP) across all sources. Source reactivity analysis further showed clear source-dependent differences: the local mixed source had the highest source reactivity for O₃ (SR(O₃)), while the biogenic transport source had the highest source reactivity for SOA (SR(SOA)). Discussion The abundant formula-assigned VOC components and the dominant contribution of oxygen-containing CHO compounds in the Qinling Mountains periphery suggest that VOCs in this transition region were chemically diverse and strongly affected by oxygenated organic compounds. The three source types showed distinct molecular characteristics. Biogenic transport was characterized by relatively higher DBE values, indicating a stronger contribution from unsaturated compounds such as plant-emitted terpenoids and their oxidation products. Anthropogenic transport showed larger molecular size and stronger oxygenated characteristics, consistent with the influence of carbonyl compounds from anthropogenic activities. The local mixed source showed the strongest oxygenated signature, suggesting that transported biogenic VOCs, anthropogenic emissions, and secondary oxidation jointly enhanced the contribution of oxygen-containing VOCs. These source-specific molecular differences further led to distinct environmental impacts: biogenic transport contributed more strongly to SOA formation potential, whereas local mixed and anthropogenic-influenced VOCs were more favorable for O₃ formation potential. Conclusions Atmospheric VOCs in the Qinling Mountains periphery showed abundant molecular composition, oxygen-containing organic compounds-dominated characteristics, and clear source dependence. Biogenic transport, anthropogenic transport, and local mixed sources differed in molecular composition, oxidation degree, carbon number distribution, and DBE characteristics, leading to distinct secondary formation potentials. Biogenic transport mainly enhanced SOA formation potential, whereas local mixed and anthropogenic-influenced VOCs were more favorable for O₃ formation potential. Recommendations and perspectives VOC control strategies in forest–urban transition regions should move beyond total VOC abundance and incorporate source-specific molecular composition and secondary formation potential. For the Qinling Mountains periphery, differentiated management should distinguish VOCs transported from forested areas from those influenced by urban emissions and local mixing. Such a source-oriented framework can provide more targeted support for coordinated O₃ and SOA pollution control in regions affected by biogenic-anthropogenic interactions.