Different chlorine and hydroxyl radical environments impact m-xylene oxidation products
Different chlorine and hydroxyl radical environments impact m-xylene oxidation products
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DOI：
10.1039/d3ea00024a
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发表时间：
2023-05-30
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影响因子：
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通讯作者：
Ruiz, Lea Hildebrandt
中科院分区：
文献类型：
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作者：
Bhattacharyya, Nirvan;Modi, Mrinali;Ruiz, Lea Hildebrandt
空气中排放的芳烃包括苯、甲苯、二甲苯和二甲苯，这些芳烃与人类活动（如运输）有关，氧化后形成二次有机气溶胶（SOA）。虽然羟基自由基（OH）占主导地位的氧化，氯自由基（Cl）与烷基取代的芳烃反应更迅速，有利于不同的氧化途径。高浓度的活性氯物种已被观察到在大陆和沿海地区，混合氯/羟基化学预计会影响区域SOA的形成和组成。本研究使用环境室实验，以评估SOA的形成和组合物的氧化间二甲苯在混合Cl/OH氧化环境。实验进行了过氧化氢（H2 O2），氯（Cl-2），和硝酰氯（ClNO 2）自由基前体在高和低NOx条件下。使用气溶胶化学形态监测器（ACSM）、扫描电迁移率系统（SEMS）和具有过滤解吸的飞行时间化学电离质谱仪（FIGAERO-CIMS）利用H3 O+和I-试剂离子收集数据。H2 O2和Cl-2实验中不同的氧化途径分别导致双环过氧化物和甲基苯醌物种。当Cl-2是唯一的自由基前体时，SOA被更高度地氧化并且更少碎片化。ClNO 2实验形成了大量的双环过氧化物和最小的甲基苯醌在气相中和较少的氧化SOA与较低的有机氯化物馏分。这些差异与二次OH的形成和较慢的ClNO 2光解驱动较低的Cl自由基浓度有关。这项研究提供的证据表明，气体和颗粒相产品的变化取决于氧化环境，并强调了研究新的氧化剂和氧化途径的重要性。
Airborne emissions of aromatic hydrocarbons including benzene, ethylbenzene, toluene, and xylenes are associated with anthropogenic activities (e.g. transportation) and form secondary organic aerosol (SOA) when oxidized. While hydroxyl radicals (OH) dominate oxidation, chlorine radicals (Cl) react with alkyl substituted aromatics more rapidly and favor a different oxidative pathway. High concentrations of reactive chlorine species have been observed in continental and coastal regions, where mixed Cl/OH chemistry is expected to influence regional SOA formation and composition. This study uses environmental chamber experiments to assess SOA formation and composition from the oxidation of m-xylene in mixed Cl/OH oxidation environments. Experiments were conducted with hydrogen peroxide (H2O2), chlorine (Cl-2), and nitryl chloride (ClNO2) radical precursors under high and low NOx conditions. Data was collected with an Aerosol Chemical Speciation Monitor (ACSM), Scanning Electrical Mobility System (SEMS) and time of flight chemical ionization mass spectrometer with filter desorption (FIGAERO-CIMS) utilizing H3O+ and I- reagent ions. Different oxidative pathways in H2O2 and Cl-2 experiments resulted in bicyclic peroxide and methylbenzoquinone species, respectively. When Cl-2 was the sole radical precursor, SOA was more highly oxidized and less fragmented. ClNO2 experiments formed substantial amounts of bicyclic peroxide and minimal methylbenzoquinone in the gas phase and less oxidized SOA with a lower fraction of organochlorides. These differences are related to secondary OH formation and slower ClNO2 photolysis driving lower Cl radical concentrations. This study provides evidence that gas and particle-phase products vary depending on the oxidative environment and underlines the importance of studying novel oxidants and oxidative pathways.