Guan Chun, Li Xinling, Zhang Wugao, Huang Zhen
Key Laboratory for Power Machinery and Engineering of M. O. E, Shanghai Jiao Tong University , Shanghai 200240, China.
J Phys Chem A. 2017 Jan 19;121(2):482-492. doi: 10.1021/acs.jpca.6b08982. Epub 2017 Jan 9.
Author: The present work, involving the formation of NO and nitrous acid (HONO) and the nitration of polycyclic aromatic hydrocarbon (PAHs) to nitro-PAHs as well as the uptake coefficients of NO, has been performed on a normal-pressure flow reactor to identify the nitration products during the heterogeneous reaction of soot toward NO in the dark and under simulated sunlight. Two types of soot particles, namely the commercial black carbon (BC) and the diesel engine soot (ES), were selected as the studied soot to compare the impacts of soot properties on heterogeneous nitration. During the whole reaction on either of the two studied soots in the dark, a fast reversible physical adsorption is observed at the very beginning, followed by a slow irreversible chemical conversion from NO to HONO and NO, in good agreement with the "reduction-oxidation" mechanism. HONO is the most abundant product during the nitration reaction on the two studied soots, contributing to 70-90% of consumed NO after 50 min exposure. Reaction orders of NO for HONO are determined as 1.20 ± 0.07 and 1.31 ± 0.04 for BC and ES, respectively, which are both close to first-order. Moreover, four sorts of PAHs compounds and their five nitro-derivatives have been identified and quantified during the reaction. About 40% and 20% of the total four measured PAHs are consumed on BC and ES, respectively, resulting in an increase in the total five measured nitro-PAHs by 21-fold on BC and 2.8-fold on ES. Finally, the impacts of light on gaseous and organics products have been investigated and the results confirm that simulated sunlight can enhance the reactivity of PAHs toward NO and cause the photolysis of newly formed nitro-compounds with more HONO formation, strongly suggesting that photochemistry of soot in the presence of NO is of great importance to be a photochemical source of HONO and would also influence the fates of PAHs and nitro-PAHs on soot.
本研究在常压流动反应器中进行，涉及一氧化氮（NO）和亚硝酸（HONO）的形成、多环芳烃（PAHs）向硝基多环芳烃（nitro-PAHs）的硝化以及NO的摄取系数，以确定在黑暗和模拟阳光条件下烟灰与NO的非均相反应过程中的硝化产物。选择了两种类型的烟灰颗粒，即商用炭黑（BC）和柴油机烟灰（ES）作为研究对象，以比较烟灰性质对非均相硝化的影响。在黑暗中对两种研究烟灰中的任何一种进行的整个反应过程中，一开始观察到快速可逆的物理吸附，随后是从NO到HONO和NO的缓慢不可逆化学转化，这与“还原-氧化”机制高度一致。HONO是两种研究烟灰硝化反应中最丰富的产物，在暴露50分钟后，消耗的NO中有70-90%转化为HONO。对于BC和ES，HONO的NO反应级数分别确定为1.20±0.07和1.31±0.04，均接近一级反应。此外，在反应过程中鉴定并定量了四种PAHs化合物及其五种硝基衍生物。在BC和ES上，分别约40%和20%的四种被测PAHs被消耗，导致BC上五种被测硝基多环芳烃总量增加21倍，ES上增加2.8倍。最后，研究了光对气态和有机产物的影响，结果证实模拟阳光可增强PAHs与NO的反应性，并导致新形成的硝基化合物发生光解，生成更多的HONO，这强烈表明在NO存在下烟灰的光化学对于成为HONO的光化学来源非常重要，并且还会影响PAHs和硝基多环芳烃在烟灰上的归宿。
