School of Engineering and Applied Sciences, Harvard University , Cambridge, Massachusetts 02138, United States.
Environ Sci Technol. 2015 Jan 6;49(1):250-8. doi: 10.1021/es5034298. Epub 2014 Dec 9.
The oxidation of isoprene is a globally significant source of secondary organic material (SOM) of atmospheric particles. The relative importance of different parallel pathways, however, remains inadequately understood and quantified. SOM production from isoprene photooxidation was studied under hydroperoxyl-dominant conditions for <5% relative humidity and at 20 °C in the presence of highly acidic to completely neutralized sulfate particles. Isoprene photooxidation was separated from SOM production by using two continuously mixed flow reactors connected in series and operated at steady state. Two online mass spectrometers separately sampled the gas and particle phases in the reactor outflow. The loss of specific gas-phase species as contributors to the production of SOM was thereby quantified. The produced SOM mass concentration was directly proportional to the loss of isoprene epoxydiol (IEPOX) isomers from the gas phase. IEPOX isomers lost from the gas phase accounted for (46 ± 11)% of the produced SOM mass concentration. The IEPOX isomers comprised (59 ± 21)% (molecular count) of the loss of monitored gas-phase species. The implication is that for the investigated reaction conditions the SOM production pathways tied to IEPOX isomers accounted for half of the SOM mass concentration.
异戊二烯的氧化是大气颗粒物中二次有机物质（SOM）的一个重要全球来源。然而，不同平行途径的相对重要性仍未得到充分理解和量化。在相对湿度 <5%、20°C 及高度酸化至完全中和的硫酸盐颗粒存在的条件下，在过氧氢主导的条件下研究了异戊二烯光氧化产生 SOM 的情况。通过使用两个串联连续混合流反应器，使异戊二烯光氧化与 SOM 生产分离，并在稳态下运行。两个在线质谱仪分别在反应器流出物中对气相和颗粒相进行采样。从而定量了作为 SOM 产生贡献者的特定气相物种的损失。产生的 SOM 质量浓度与气相中异戊二烯环氧化物（IEPOX）异构体的损失直接成正比。气相中损失的 IEPOX 异构体占产生的 SOM 质量浓度的 (46 ± 11)%。IEPOX 异构体占监测到的气相物种损失的 (59 ± 21)%（分子计数）。这意味着在所研究的反应条件下，与 IEPOX 异构体相关的 SOM 生成途径占 SOM 质量浓度的一半。
