Emissions of biogenic reactive carbon significantly influence atmospheric chemistry, contributing to the formation and destruction of secondary pollutants, such as secondary organic aerosol and ozone. While isoprene and monoterpenes are a major fraction of emissions and have been extensively studied, substantially less is known about the atmospheric impacts of higher-molecular-weight terpenes such as sesquiterpenes. In particular, sesquiterpenes have been proposed to play a significant role in ozone chemical loss due to the very high ozone reaction rates of certain isomers. However, relatively little data are available on the isomer-resolved composition of this compound class or its role in ozone chemistry. This study examines the chemical diversity of sesquiterpenes and availability of ozone reaction rate constants to evaluate the current understanding of their ozone reactivity. Sesquiterpenes are found to be highly diverse, with 72 different isomers reported and relatively few isomers that contribute a large mass fraction across all studies. For the small number of isomers with known ozone reaction rates, estimated rates may be 25 times higher or lower than measurements, indicating that estimated reaction rates are highly uncertain. Isomers with known ozone reaction rates make up approximately half of the mass of sesquiterpenes in concentration and emission measurements. Consequently, the current state of the knowledge suggests that the total ozone reactivity of sesquiterpenes cannot be quantified without very high uncertainty, even if isomer-resolved composition is known. These results are in contrast to monoterpenes, which are less diverse and for which ozone reaction rates are well-known, and in contrast to hydroxyl reactivity of monoterpenes and sesquiterpenes, for which reaction rates can be reasonably well estimated. Improved measurements of a relatively small number of sesquiterpene isomers would reduce uncertainties and improve our understanding of their role in regional and global ozone chemistry.

中文翻译：

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倍半萜臭氧分解率和成分的缺失测量限制了对大气反应性的了解

生物活性碳的排放显着影响大气化学，导致二次污染物（例如二次有机气溶胶和臭氧）的形成和破坏。虽然异戊二烯和单萜是排放的主要部分，并且已被广泛研究，但人们对倍半萜等较高分子量萜烯对大气的影响知之甚少。特别地，由于某些异构体的非常高的臭氧反应速率，倍半萜烯已被认为在臭氧化学损失中发挥重要作用。然而，关于此类化合物的异构体拆分组成或其在臭氧化学中的作用的数据相对较少。本研究检查了倍半萜烯的化学多样性和臭氧反应速率常数的可用性，以评估目前对其臭氧反应性的了解。倍半萜烯被发现高度多样化，报告了 72 种不同的异构体，并且在所有研究中贡献较大质量分数的异构体相对较少。对于已知臭氧反应速率的少量异构体，估计速率可能比测量值高或低 25 倍，表明估计反应速率高度不确定。在浓度和排放测量中，具有已知臭氧反应速率的异构体约占倍半萜烯质量的一半。因此，目前的知识状况表明，即使异构体解析的组成已知，倍半萜烯的总臭氧反应性也无法在没有非常高的不确定性的情况下进行量化。这些结果与单萜形成鲜明对比，单萜的多样性较低，臭氧反应速率是众所周知的，并且与单萜和倍半萜的羟基反应性形成鲜明对比，单萜和倍半萜的羟基反应性可以很好地估计反应速率。改进对相对少量倍半萜异构体的测量将减少不确定性，并加深我们对其在区域和全球臭氧化学中的作用的理解。