Abstract:

Greening vegetation provides various ecological benefits, but the biogenic volatile organic compounds (BVOCs) released by plants are the main precursors of ozone (O₃) and secondary organic aerosols (SOA). It is crucial to investigate the BVOCs emission characteristics of typical plants in different regions to formulate more targeted air pollution prevention and control measures. Current studies on BVOCs emissions from greening species in Beijing have primarily focused on isoprene and monoterpenes, but few studies have investigated the emission characteristics of sesquiterpenes and other volatile organic compounds. Therefore, to understand the BVOCs emission characteristics and secondary pollutant formation potentials of the dominant greening trees in Beijing, this study collected samples and analyzed the BVOCs components of nine tree species in Beijing using the dynamic headspace method and gas chromatography/mass spectrometry from July to August 2022. We calculated the standardized BVOCs emission rates for each tree species and evaluated their potential for secondary pollutant formation. The results showed that the BVOCs emission rates varied significantly among the nine tree species. The total BVOCs emission rates of Platanus occidentalis, Populus tomentosa, and Salix matsudana were relatively high, reaching 26.3, 22.5, and 22.2 µg·g⁻¹·h⁻¹, respectively. The VOCs emission rates of Quercus mongolica, Pinus tabuliformis, and Sophora japonica were 15.9, 14.4, and 6.94 µg·g⁻¹·h⁻¹, respectively. In contrast, the BVOCs emission rates of Platycladus orientalis, Ginkgo biloba, and Fraxinus chinensis were relatively low at 3.36, 1.73, and 1.35 µg·g⁻¹·h⁻¹, respectively. The composition of BVOCs emitted by different tree species varied significantly. Generally, coniferous species emitted monoterpenes at high rates, whereas broad-leaved species exhibited high emission rates of isoprene and oxygenated BVOCs. The highest emission rates of monoterpenes, isoprene and oxygenated BVOCs were Pinus tabuliformis (11.2 µg·g⁻¹·h⁻¹), Populus tomentosa (14.5 µg·g⁻¹·h⁻¹) and Platanus occidentalis (17.7 µg·g⁻¹·h⁻¹), respectively. The emission rates of sesquiterpenes, aromatic hydrocarbons, and alkanes were relatively low among the nine tree species. Tree species with high BVOCs emission rates make significant contributions to environmental secondary pollutants. Populus tomentosa, Salix matsudana, and Platanus occidentalis had a high potential for O₃ formation, whereas Pinus tabuliformis had a high potential for SOA formation. These factors should be carefully considered in future urban-greening projects. This study has important implications for the selection of tree species for urban greening in northern China.

Key words: volatile organic compounds, emission rates, emission profile, secondary pollutants, ozone formation potential

摘要： 为了解北京地区主要树种的BVOCs排放特征及其对大气污染的影响，选择9种典型绿化树种的成年植株作为研究对象，利用动态顶空法和气相色谱-质谱法，于2022年7-8月进行采样和分析，监测树种排放的BVOCs组分和排放速率，并对其O₃和SOA生成潜势进行评估。结果显示：不同树种的BVOCs排放速率差异显著，一球悬铃木（Platanus occidentalis）、毛白杨（Populus tomentosa）和垂柳（Salix matsudana）排放速率较高，分别为C 26.3、22.5和22.2 µg·g⁻¹·h⁻¹；侧柏（Platycladus orientalis）、银杏（Ginkgo biloba）和白蜡（Fraxinus chinensis）的BVOCs排放速率较低，分别为C 3.36、1.73、1.35 µg·g⁻¹·h⁻¹。不同树种排放的BVOCs组分存在明显差异，针叶树种油松（Pinus tabuliformis）和侧柏主要排放单萜烯，其他7种阔叶树种主要排放异戊二烯和含氧VOCs。其中，单萜烯排放速率最高的是油松，为C 11.2 µg·g⁻¹·h⁻¹；异戊二烯排放速率最高的是毛白杨，为C 14.5 µg·g⁻¹·h⁻¹；含氧VOCs排放速率最高的是一球悬铃木，为C 17.7 µg·g⁻¹·h⁻¹。倍半萜烯、芳香烃和烷烃在各树种中的排放速率均较低。高BVOCs排放树种对环境二次污染物有显著贡献，毛白杨、垂柳和一球悬铃木具有较高的O₃生成潜势，油松具有较高的SOA生成潜势，在未来城市绿化中应谨慎考虑。银杏和白蜡的二次污染物生成潜势低，从提升空气质量角度看是较理想的绿化树种。

关键词: 挥发性有机物, 释放速率, 排放成分谱, 二次污染物, 臭氧生成潜势