Department of Ecology and Evolutionary Biology, University of California Irvine, Irvine, CA, USA.
Department of Chemistry, University of California Irvine, Irvine, CA, USA.
Environ Sci Process Impacts. 2024 Jul 17;26(7):1156-1170. doi: 10.1039/d4em00063c.
One major challenge in predicting secondary organic aerosol (SOA) formation in the atmosphere is incomplete representation of biogenic volatile organic compounds (BVOCs) emitted from plants, particularly those that are emitted as a result of stress - a condition that is becoming more frequent in a rapidly changing climate. One of the most common types of BVOCs emitted by plants in response to environmental stress are acyclic terpenes. In this work, SOA is generated from the photooxidation of acyclic terpenes in an oxidation flow reactor and compared to SOA production from a reference cyclic terpene - α-pinene. The acyclic terpenes used as SOA precursors included β-myrcene, β-ocimene, and linalool. Results showed that oxidation of all acyclic terpenes had lower SOA yields measured after 4 days photochemical age, in comparison to α-pinene. However, there was also evidence that the condensed organic products that formed, while a smaller amount overall, had a higher oligomeric content. In particular, β-ocimene SOA had higher oligomeric content than all the other chemical systems studied. SOA composition data from ultra-high performance liquid chromatography with electrospray ionization mass spectrometry (UHPLC-ESI-MS) was combined with mechanistic modeling using the Generator for Explicit Chemistry and Kinetics of Organics in the Atmosphere (GECKO-A) to explore chemical mechanisms that could lead to this oligomer formation. Calculations based on composition data suggested that β-ocimene SOA was more viscous with a higher glass transition temperature than other SOA generated from acyclic terpene oxidation. This was attributed to a higher oligomeric content compared to other SOA systems studied. These results contribute to novel chemical insights about SOA formation from acyclic terpenes and relevant chemistry processes, highlighting the importance of improving underrepresented biogenic SOA formation in chemical transport models.
在预测大气中二次有机气溶胶 (SOA) 形成方面，一个主要挑战是对植物排放的生物挥发性有机化合物 (BVOC) 代表性不足，尤其是那些因快速变化的气候导致的压力下排放的 BVOC。植物在应对环境压力时排放的最常见的 BVOC 之一是无环萜烯。在这项工作中，在氧化流动反应器中通过光氧化无环萜烯来生成 SOA，并将其与参考环状萜烯-α-蒎烯的 SOA 生成进行比较。用作 SOA 前体的无环萜烯包括β-月桂烯、β-罗勒烯和芳樟醇。结果表明，与 α-蒎烯相比，所有无环萜烯在 4 天光化学龄后氧化生成的 SOA 产率较低。然而，也有证据表明，尽管形成的凝聚有机产物总量较少，但它们的聚合含量更高。特别是，β-罗勒烯 SOA 的聚合含量高于研究的所有其他化学体系。通过超高效液相色谱与电喷雾电离质谱 (UHPLC-ESI-MS) 获得的 SOA 组成数据与使用大气中有机物的显式化学和动力学生成器 (GECKO-A) 的机制建模相结合，探索了可能导致这种聚合形成的化学机制。基于组成数据的计算表明，与其他无环萜烯氧化生成的 SOA 相比，β-罗勒烯 SOA 的粘性更大，玻璃化转变温度更高。这归因于与其他研究的 SOA 体系相比，它具有更高的聚合含量。这些结果为无环萜烯生成 SOA 的新化学见解和相关化学过程做出了贡献，强调了在化学输送模型中改进代表性不足的生物源 SOA 形成的重要性。
