Size resolved chemical composition of nanoparticles from reactions of sulfuric acid with ammonia and dimethylamine
Size resolved chemical composition of nanoparticles from reactions of sulfuric acid with ammonia and dimethylamine
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DOI：
10.1080/02786826.2018.1490005
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发表时间：
2018-01-01
影响因子：
5.2
通讯作者：
Smith, James N.
中科院分区：
文献类型：
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作者：
Chen, Haihan;Chee, Sabrina;Smith, James N.
通过将气相硫酸（H2SO 4）与氨（NH3）或二甲胺（DMA）引入到流动管反应器中，研究了酸碱化学驱动的纳米颗粒形成和生长。热解吸化学电离质谱仪用于测量在干燥条件下和在60%相对湿度下形成的H2SO 4-DMA和H2SO 4- NH3纳米颗粒的尺寸分辨化学组成。与预测的散装水溶液体系相比，纳米粒子表现出很强的尺寸依赖性的组成梯度，并不总是达到完全中和的状态，在过量的气相碱。较小的颗粒酸性更强，在干燥和潮湿条件下形成的8.6和9.5nm H2SO 4-DMA颗粒的酸碱比分别为0.7 ± 0.1和1.3 ± 0.3，在干燥和潮湿条件下形成的7.5nm H2SO 4-NH3颗粒的酸碱比分别为3.1 ± 0.6和3.4 ± 0.3。颗粒的酸度一般随颗粒的增大而降低。当H2SO 4-DMA颗粒生长到14 nm时，它们变得完全中和，但12 nm处的H2SO 4-NH3颗粒仍然是酸性的，并且在本研究的实验条件下从未观察到达到本体样品热力学平衡。热力学模型表明，通过修改酸解离常数以最大限度地减少可能由空间或混合效应引起的酸碱化学反应，以及考虑中性碱的挥发，可以重现观察到的趋势。Copyright（c）2018 American Association for Aerosol Research
Nanoparticle formation and growth driven by acid-base chemistry was investigated by introducing gas-phase sulfuric acid (H2SO4) with ammonia (NH3) or dimethylamine (DMA) into a flow tube reactor. A thermal desorption chemical Ionization mass spectrometer was used to measure the size-resolved chemical composition of H2SO4-DMA and H2SO4- NH3 nanoparticles formed under dry conditions and at 60% relative humidity. In contrast with predictions for bulk aqueous systems, nanoparticles showed a strong size-dependent composition gradient and did not always reach a fully neutralized state in excess of gas-phase base. Smaller particles were more acidic, with an acid:base ratio of 0.70.1 and 1.3 +/- 0.3 for 8.6 and 9.5nm H2SO4-DMA particles formed under dry and humid conditions, respectively, and 3.1 +/- 0.6 and 3.4 +/- 0.3 for 7.5nm H2SO4-NH3 particles formed under dry and humid conditions, respectively. The acidity of particles generally decreased as particles grew. H2SO4-DMA particles became fully neutralized as they grew to 14nm, but H2SO4-NH3 particles at 12nm were still acidic and were never observed to reach bulk sample thermodynamic equilibrium for the experimental conditions in this study. Thermodynamic modeling demonstrated that the observed trends can be reproduced by modifying acid dissociation constants to minimize acid-base chemistry, which may be caused by steric or mixing effects, and by considering volatilization of the neutral base.Copyright (c) 2018 American Association for Aerosol Research