Atmospheric Chemistry of Volatile Methyl Siloxanes: Kinetics and Products of Oxidation by OH Radicals and Cl Atoms
Atmospheric Chemistry of Volatile Methyl Siloxanes: Kinetics and Products of Oxidation by OH Radicals and Cl Atoms
复制标题
DOI：
10.1021/acs.est.0c01368
复制
发表时间：
2020-05-19
影响因子：
11.4
通讯作者：
Browne, Eleanor C.
中科院分区：
文献类型：
--
作者：
Alton, Mitchell W.;Browne, Eleanor C.
挥发性甲基硅氧烷(VMS)是一种普遍存在的人为污染物，近年来因其潜在的毒性和环境持久性而受到关注。在这项工作中，我们测定了在297+/-3K和大气压下，六甲基二硅氧烷(L2)、八甲基三硅氧烷(L3)、十甲基四硅氧烷(L4)、十二甲基五硅氧烷(L5)、六甲基环三硅氧烷(D3)、八甲基环四硅氧烷(D4)和十甲基环五硅氧烷(D5)在Boulder、CO(类似于860mbar)中被OH自由基和氯原子氧化的速率常数。测得含羟基的速率常数为(1.20+/-0.09)x10(-12)、(1.7+/-0.1)x10(-12)、(2.5+/-0.2)x10(-12)、(3.4+/-0.5)x10(-12)、(0.86+/-0.09)x10(-12)、(1.3+/-0.1)x10(-12)、L2、L3、L4、L5、D3、D4和D5分别为(2.1+/-0.1)×10(-12)cm(3)molec(-1)S(-1)。反应速率常数分别为(1.44+/-0.05)x10(-10)，(1.85+/-0.05)x10(-10)，(2.2+/-0.1)x10(-10)，(2.9+/-0.1)x10(-10)，(0.56+/-0.05)x10(-10)，(1.16+/-0.08)x10(-10)，和(1.80+/-0.1)×10(-10)cm(3)摩尔比(-1)和S(-1)。本文提出了F(-Si(CH3)(2)OR)和F(-SiCH3(OR)(2))的取代基因子，用于估算OH自由基速率常数的通用模型AOPWIN。氯原子可以在全球范围内消除VMS的百分比水平，这可能会增加城市地区的重要性。
Volatile methyl siloxanes (VMS) are ubiquitous anthropogenic pollutants that have recently come under scrutiny for their potential toxicity and environmental persistence. In this work, we determined the rate constants for oxidation by OH radicals and Cl atoms at 297 +/- 3 K and atmospheric pressure in Boulder, CO (similar to 860 mbar) of hexamethyldisiloxane (L2), octamethyltrisiloxane (L3), decamethyltetrasiloxane (L4), dodecamethylpentasiloxane (L5), hexamethylcyclotrisiloxane (D3), octamethylcyclotetrasiloxane (D4), and decamethylcyclopentasiloxane (D5). Measured rate constants with OH radicals were (1.20 +/- 0.09) x 10(-12), (1.7 +/- 0.1) x 10(-12), (2.5 +/- 0.2) x 10(-12), (3.4 +/- 0.5) x 10(-12), (0.86 +/- 0.09) x 10(-12), (1.3 +/- 0.1) x 10(-12), and (2.1 +/- 0.1) x 10(-12) cm(3) molec(-1) s(-1), for L2, L3, L4, L5, D3, D4, and D5, respectively. The rate constants for reactions with CI atoms with the same compounds were (1.44 +/- 0.05) x 10(-10), (1.85 +/- 0.05) x 10(-10), (2.2 +/- 0.1) x 10(-10), (2.9 +/- 0.1) x 10(-10), (0.56 +/- 0.05) x 10(-10), (1.16 +/- 0.08) x 10(-10), and (1.8 +/- 0.1) x 10(-10) cm(3) molec(-1) s(-1), respectively. Substituent factors of F(-Si(CH3)(2)OR) and F(-SiCH3(OR)(2)) are proposed for use in AOPWIN, a common model for OH radical rate constant estimations. Cl atoms can remove percentage levels of VMS globally with potentially increased importance in urban areas.