Ballesteros Bernabé, Ceacero-Vega Antonio A, Jiménez Elena, Albaladejo José
Department of Physical Chemistry, Faculty of Chemical Sciences and Technologies, University of Castilla-La Mancha, Avda. Camilo José Cela s/n, 13071, Ciudad Real, Spain.
Environ Sci Pollut Res Int. 2015 Apr;22(7):4806-19. doi: 10.1007/s11356-014-2901-0. Epub 2014 May 3.
As the result of biogenic and anthropogenic activities, large quantities of chemical compounds are emitted into the troposphere. Alkanes, in general, and cycloalkanes are an important chemical class of hydrocarbons found in diesel, jet and gasoline, vehicle exhaust emissions, and ambient air in urban areas. In general, the primary atmospheric fate of organic compounds in the gas phase is the reaction with hydroxyl radicals (OH). The oxidation by Cl atoms has gained importance in the study of atmospheric reactions because they may exert some influence in the boundary layer, particularly in marine and coastal environments, and in the Arctic troposphere. The aim of this paper is to study of the atmospheric reactivity of methylcylohexanes with Cl atoms and OH radicals under atmospheric conditions (in air at room temperature and pressure). Relative kinetic techniques have been used to determine the rate coefficients for the reaction of Cl atoms and OH radicals with methylcyclohexane, cis-1,4-dimethylcyclohexane, trans-1,4-dimethylcyclohexane, and 1,3,5-trimethylcyclohexane at 298 ± 2 K and 720 ± 5 Torr of air by Fourier transform infrared) spectroscopy and gas chromatography-mass spectrometry (GC-MS) in two atmospheric simulation chambers. The products formed in the reaction under atmospheric conditions were investigated using a 200-L Teflon bag and employing the technique of solid-phase microextraction coupled to a GC-MS. The rate coefficients obtained for the reaction of Cl atoms with the studied compounds are the following ones (in units of 10(-10) cm(3) molecule(-1) s(-1)): (3.11 ± 0.16), (2.89 ± 0.16), (2.89 ± 0.26), and (2.61 ± 0.42), respectively. For the reactions with OH radicals the determined rate coefficients are (in units of 10(-11) cm(3) molecule(-1) s(-1)): (1.18 ± 0.12), (1.49 ± 0.16), (1.41 ± 0.15), and (1.77 ± 0.23), respectively. The reported error is twice the standard deviation. A detailed mechanism for ring-retaining product channels is proposed to justify the observed reaction products. The global tropospheric lifetimes estimated from the reported OH- and Cl-rate coefficients show that the main removal path for the investigated methylcyclohexanes is the reaction with OH radicals. But in marine environments, after sunrise, Cl reactions become more important in the tropospheric degradation. Thus, the estimated lifetimes range from 16 to 24 h for the reactions of the OH radical (calculated with [OH] = 10(6) atoms cm(-3)) and around 7-8 h in the reactions with Cl atoms in marine environments (calculated with [Cl] = 1.3 × 10(5) atoms cm(-3)). The reaction of Cl atoms and OH radicals and methylcylohexanes can proceed by H abstraction from the different positions.
由于生物源和人为活动的结果，大量化合物被排放到对流层。一般来说，烷烃和环烷烃是柴油、喷气燃料、汽油、车辆尾气排放以及城市地区环境空气中发现的一类重要的碳氢化合物。通常，气相中有机化合物在大气中的主要归宿是与羟基自由基（OH）反应。氯原子的氧化作用在大气反应研究中变得越来越重要，因为它们可能在边界层，特别是在海洋和沿海环境以及北极对流层中产生一些影响。本文的目的是研究在大气条件下（室温常压的空气中）甲基环己烷与氯原子和羟基自由基的大气反应活性。已使用相对动力学技术，通过傅里叶变换红外光谱和气相色谱 - 质谱联用（GC - MS），在两个大气模拟室中测定了氯原子和羟基自由基与甲基环己烷、顺式 - 1,4 - 二甲基环己烷、反式 - 1,4 - 二甲基环己烷以及1,3,5 - 三甲基环己烷在298 ± 2 K和720 ± 5 Torr空气条件下反应的速率系数。使用一个200升的特氟龙袋，并采用固相微萃取与GC - MS联用技术，研究了大气条件下反应生成的产物。氯原子与所研究化合物反应得到的速率系数如下（单位为10^(-10) cm³ molecule⁻¹ s⁻¹）：分别为(3.11 ± 0.16)、(2.89 ± 0.16)、(2.89 ± 0.26)和(2.61 ± 0.42)。对于与羟基自由基的反应，测定的速率系数（单位为10^(-11) cm³ molecule⁻¹ s⁻¹）分别为：(1.18 ± 0.12)、(1.49 ± 0.16)、(1.41 ± 0.15)和(1.77 ± 0.23)。报告的误差是标准偏差的两倍。提出了一个用于保留环产物通道的详细机理，以解释观察到的反应产物。根据报告的与OH和Cl的速率系数估算的全球对流层寿命表明，所研究的甲基环己烷的主要去除途径是与羟基自由基反应。但在海洋环境中，日出后，氯反应在对流层降解中变得更加重要。因此，对于与羟基自由基的反应（按[OH] = 10⁶ atoms cm⁻³计算），估算的寿命范围为16至24小时，而在海洋环境中与氯原子反应（按[Cl] = 1.3 × 10⁵ atoms cm⁻³计算）的寿命约为7至8小时。氯原子、羟基自由基与甲基环己烷的反应可以通过从不同位置夺取氢原子来进行。
