In this study, we developed an observation based photochemical box model with the measurement data collected at a suburban site (i.e., the Xianghe, XH site) of the Beijing-Tianjin-Hebei (BTH) region and the latest version of the Master Chemical Mechanism (MCM v3.3.1), which newly incorporated 498 reaction for the additional 155 species with the oxidation of isoprene by the OH radical. The influence of updated isoprene degradation on the radical budgets, formation of intermediate and secondary products by comparing the simulation results in the original version (MCM v3.2) was firstly analyzed to estimate whether the updates of precursors could influence the model performance on its evolution pathways and related products. The results demonstrated that though the input of isoprene could significantly decrease or increase the concentrations of OH and HO radicals in the model simulation, respectively, the difference in the simulated concentrations of these radicals with isoprene oxidation before and after the updates was not statistically significant. For intermediate products, the simulated concentrations of formaldehyde and methacrolein (MACR) did not significantly alter before and after the updates, while the abundance of methyl vinyl ketone (MVK) reduced obviously (the maximum reduction of 31%) due to lower reaction coefficient between ISOPBO2 and NO and the lower branching ratios caused by the newly added pathways involving CISOPA and TISOPA in the updated scheme. On the other hand, the simulation concentrations of acrolein (ACR), glyoxal (Gly) and methylglyoxal (Mgly) increased significantly after the model updates. The dominant pathway for the increment of ACR was the decomposition of CH2CHCH2O produced by PE4E2CO, while those of Gly and Mgly were associated with radicals of C537O and PACLOOA that were both from the new intermediate radical of CISOPC. In addition, 39 isoprene oxidation products among the 155 new added species were identified to partition in the formation of secondary organic aerosol (SOA), which were coupled in the gas-particle partitioning module to optimize the formation of SOA, contributing 1.15 μg m to the increase of SOA mean concentration. The updates of isoprene degradation further resulted in the significant change for its sensitivity in SOA formation, making it as the secondary important SOA precursor at the XH site. Last but not the least, the influence on photochemical ozone formation related to updates of isoprene degradation was ignorable. Overall, the above results confirmed the insufficient description of the degradation of precursors indeed limited the simulation of the intermediate and secondary products, highlighting the needs of exploring and parameterizing the precursor degradation processes for better understanding of their behaviors and SOA formation in the atmosphere.

中文翻译：

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更新的异戊二烯氧化机制对 MCM v3.3.1 中中间产物和次级产物形成的影响

在本研究中，我们利用京津冀（BTH）地区郊区站点（即香河、XH站点）收集的测量数据和最新版本的Master Chemical Mechanism，开发了基于观测的光化学盒模型(MCM v3.3.1)，其中新纳入了另外 155 种异戊二烯被 OH 自由基氧化的 498 个反应。首先通过比较原始版本（MCM v3.2）中的模拟结果，分析更新的异戊二烯降解对自由基预算、中间产物和次级产物形成的影响，以估计前体的更新是否会影响模型演化的性能途径和相关产品。结果表明，虽然异戊二烯的输入可以分别显着降低或增加模型模拟中OH和HO自由基的浓度，但更新前后异戊二烯氧化的这些自由基的模拟浓度差异不具有统计学意义。对于中间产品，甲醛和异丁烯醛（MACR）的模拟浓度在更新前后没有显着变化，而甲基乙烯基酮（MVK）的丰度由于两者之间的反应系数较低而明显降低（最大降低了31%）。 ISOPBO2 和 NO 以及更新方案中新添加的涉及 CISOPA 和 TISOPA 的途径导致的较低支化比。另一方面，模型更新后丙烯醛（ACR）、乙二醛（Gly）和甲基乙二醛（Mgly）的模拟浓度显着增加。 ACR增加的主要途径是PE4E2CO分解产生CH2CHCH2O，而Gly和Mgly的分解则与C537O和PACLOOA自由基相关，这两个自由基都来自CISOPC的新中间自由基。此外，在155个新添加的物种中，确定了39种异戊二烯氧化产物在二次有机气溶胶（SOA）的形成中进行分配，这些产物在气体-颗粒分配模块中耦合以优化SOA的形成，贡献了1.15 μg m SOA 平均浓度的增加。异戊二烯降解的更新进一步导致其对SOA形成的敏感性发生显着变化，使其成为XH位点第二重要的SOA前体。最后但并非最不重要的一点是，与异戊二烯降解更新相关的对光化学臭氧形成的影响可以忽略不计。总的来说，上述结果证实对前体降解的描述不充分确实限制了中间产物和次级产物的模拟，凸显了探索和参数化前体降解过程的需要，以更好地了解它们的行为和大气中SOA的形成。