Formation of highly oxygenated organic molecules from chlorine-atom-initiated oxidation of alpha-pinene
Formation of highly oxygenated organic molecules from chlorine-atom-initiated oxidation of alpha-pinene
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DOI：
10.5194/acp-2019-807
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发表时间：
2019-10
影响因子：
6.3
通讯作者：
Yonghong Wang;M. Riva;Hongbin Xie;L. Heikkinen;S. Schallhart;Q. Zha;Chao Yan;Xucheng He;O. Per
中科院分区：
文献类型：
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作者：
Yonghong Wang;M. Riva;Hongbin Xie;L. Heikkinen;S. Schallhart;Q. Zha;Chao Yan;Xucheng He;O. Per
抽象的。α-蒎烯在大气中氧化产生的高含氧有机分子（HOM）可以不可逆地凝结成颗粒，并有助于二次有机气溶胶（SOA）的形成。最近，硝基氯（ClNO 2）的形成从非均相反应，其次是其随后的光解，被认为是氯原子在大气中的许多地方的一个重要来源。然而，氯原子对α-蒎烯等单萜类化合物的氧化作用很少受到关注，而且该反应形成HOM的能力也完全未被研究。在此，在低氮氧化物和高氮氧化物（NOx，NOx=NO+NO2）条件下用α-蒎烯和氯进行室实验。使用基于硝酸盐的CI-APi-ToF（化学电离-大气压界面-飞行时间）质谱仪来测量HOM产物。在低NOx条件下，观察到具有9-10个碳原子的单体和具有18-20个碳原子的二聚体的明显分布。随着室内NOx浓度的增加，由于过氧自由基与NO的反应，二聚体的形成受到抑制。我们估计在低NOx条件下氯引发的α-蒎烯氧化的HOM产率约为1.8%，但由于缺乏合适的校准方法，具有很大的不确定性范围（0.8%-4%）。由于同时发生臭氧分解反应，因此无法确定高NOx下的相应产率。我们的研究表明，α-蒎烯也被氯原子氧化，并产生低挥发性有机化合物。
Abstract. Highly oxygenated organic molecules (HOMs) from atmospheric oxidation of alpha-pinene can irreversibly condense to particles and contribute to secondary organic aerosol (SOA) formation. Recently, the formation of nitryl chloride (ClNO2) from heterogeneous reactions, followed by its subsequent photolysis, is suggested to be an important source of chlorine atoms in many parts of the atmosphere. However, the oxidation of monoterpenes such as alpha-pinene by chlorine atoms has received very little attention, and the ability of this reaction to form HOMs is completely unstudied. Here, chamber experiments were conducted with alpha-pinene and chlorine under low- and high-nitrogen-oxide (NOx, NOx=NO+NO2) conditions. A nitrate-based CI-APi-ToF (chemical ionization–atmospheric pressure interface–time of flight) mass spectrometer was used to measure HOM products. Clear distributions of monomers with 9–10 carbon atoms and dimers with 18–20 carbon atoms were observed under low-NOx conditions. With increased concentration of NOx within the chamber, the formation of dimers was suppressed due to the reactions of peroxy radicals with NO. We estimated the HOM yields from chlorine-initiated oxidation of alpha-pinene under low-NOx conditions to be around 1.8 %, though with a substantial uncertainty range (0.8 %–4 %) due to lack of suitable calibration methods. Corresponding yields at high NOx could not be determined because of concurrent ozonolysis reactions. Our study demonstrates that also the oxidation of alpha-pinene by chlorine atoms and yield low-volatility organic compounds.