Smog chamber simulation on heterogeneous reaction of O3 and NO2 on black carbon under various relative humidity conditions.
Smog chamber simulation on heterogeneous reaction of O3 and NO2 on black carbon under various relative humidity conditions.
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不同相对湿度条件下O3和NO2在炭黑上非均相反应的烟雾室模拟。
DOI：
10.1016/j.scitotenv.2022.153649
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发表时间：
2022-02
影响因子：
9.8
通讯作者：
Gehui Wang
中科院分区：
文献类型：
--
作者：
Si Zhang;Xinbei Xu;Yali Lei;Dapeng Li;Yiqian Wang;Shijie Liu;Can Wu;Shuangshuang Ge;Gehui Wang
在实验室烟雾箱中，模拟了NH3存在下，O3与NO2在黑碳（BC）和KCl处理过的BC表面反应生成硝酸盐的非均相过程。结果表明，气相中O3和NO2迅速反应生成N2 O 5，N2 O 5水解生成HNO 3，在BC表面与NH3进一步中和生成NH 4 NO3，沿着少量N2 O 5与BC表面活性位反应分解为NO和NO2。同时，分形BC聚集体在NH 4 NO3包覆过程中发生了重组并凝聚成球形颗粒。与单独暴露于NO2或O3时相比，同时暴露于NO2和O3时出现了较强的CH 2 O+、CH 2 O2+和CH 4 NO+信号，表明NO2和O3的协同氧化作用显著活化了BC表面，形成了羰基、羧基和硝基，促进了水蒸气在BC表面的吸附，促进了NH 4 NO3的生成.在<75 ± 2%RH条件下，NH 4 NO3在BC表面的包覆过程包括N2 O 5在BC表面的扩散和随后的水解，这是由于吸附的水分子数量有限。而在90 ± 2%RH条件下，N2 O 5在BC表面的水相中由于多层水分子的吸附而直接发生水解，导致NH 4 NO3在BC表面瞬间生成，没有任何延迟。NH_4NO_3在KCl处理的BC颗粒上的包覆速率比在纯BC颗粒上的包覆速率在初始阶段快3-4倍，表明NH_4NO_3的形成增加，这主要是由于KCl盐增强了BC的吸湿性。
In this study, heterogeneous formation of nitrate from O3reaction with NO2on black carbon (BC) and KCl-treated BC surface in the presence of NH3was simulated under 30–90% RH conditions by using a laboratory smog chamber. We found that O3and NO2in the chamber quickly reacted into N2O5in the gas phase,which subsequently hydrolyzed into HNO3and further neutralized with NH3into NH4NO3on the BC surface, along with a small amount of N2O5decomposed into NO and NO2through a reaction with the BC surface active site. Meanwhile, the fractal BC aggregates restructured and condensed to spherical particles during the NH4NO3coating process. Compared to that during the exposure to NO2or O3alone, the presence of strong signals of CH2O+, CH2O2+and CH4NO+during the simultaneous exposure to both NO2and O3suggested a synergetic oxidizing effect of NO2and O3, which significantly activated the BC surface by forming carbonyl, carboxylic and nitro groups, promoted the adsorption of water vapor onto the BC surface and enhanced the NH4NO3formation. Under <75 ± 2% RH conditions the coating process of NH4NO3on the BC surface consisted of a diffusion of N2O5onto the surface and a subsequent hydrolysis, due to the limited number of water molecules adsorbed. However, under 90 ± 2% RH conditions N2O5directly hydrolyzed on the aqueous phase of the BC surface due to the multilayer water molecules adsorbed, which caused an instant NH4NO3formation on the surface without any delay. The coating rate of NH4NO3on KCl-treated BC particles was 3–4 times faster than that on the pure BC particles at the initial stage, indicating an increasing formation of NH4NO3, mainly due to an enhanced hygroscopicity of BC by KCl salts.
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