混合柠檬酸/（NH4）2SO4 / H2O颗粒的蒸发：使用光学镊子蒸发有机气溶胶。,Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy

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混合柠檬酸/（NH4）2SO4 / H2O颗粒的蒸发：使用光学镊子蒸发有机气溶胶。
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy ( IF 4.3 ) Pub Date : 2019-10-12 , DOI: 10.1016/j.saa.2019.117552
Xi-Juan Lv ₁ , Zhe Chen ₂ , Jia-Bi Ma ₂ , Yun-Hong Zhang ₂

Affiliation

大气气溶胶中的半挥发性有机化合物（SVOC）的冷凝和蒸发过程可引起其化学和物理性质的显着变化。因此，为了解释和预测大气气溶胶的成分变化，必不可少的是要了解SVOC在冷凝和气相之间的分配行为。在这项研究中，使用光镊结合腔增强拉曼光谱技术观察内部混合柠檬酸（CA）/（NH4）2SO4（AS）颗粒的挥发性，以及AS对其气体/颗粒分配行为的影响。研究了大气有机酸。从模拟拉曼光谱的波长位置实时确定悬浮液滴的半径和折射率，并根据麦克斯韦方程获得在不同相对湿度（RHs）下CA的有效蒸气压。对于有机/无机摩尔比（OIR）为1：1的CA / AS颗粒，CA的有效蒸气压随RH的降低而降低。当RH从67％降至8.2％时，CA的有效蒸气压从（1.35±0.508）×10-4Pa降至（3.0±1.0）×10-6Pa。同时，对OIR为3：1、1：3的CA / AS颗粒进行了研究，结果表明与OIR为1：1的颗粒相比，存在相同的现象。在相对湿度下，CA的有效蒸气压随AS含量的增加而降低，提示AS的存在抑制了CA在水性颗粒中的分配。此外，还进一步研究了CA和CA / AS / H2O系统中水的传质过程。液滴半径和RH之间的特征时间比用于描述取决于RH的水传质差异。与纯CA的特征时间比相比，CA / AS颗粒的特征时间比明显增加。对于在相同RH步骤下的CA / AS粒子，特征时间比随AS含量的增加而增加。根据微分等温线，分别计算了柠檬酸和柠檬酸/硫酸铵在低相对湿度（RH≈7％-1％，RH≈1％-7％）时的扩散系数。一般来说，

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Evaporation of mixed citric acid/(NH4)2SO4/H2O particles: Volatility of organic aerosol by using optical tweezers.

The condensation and evaporation processes of semi-volatile organic compounds (SVOCs) in atmospheric aerosols can induce significant evolutions of their chemical and physical properties. Hence, for interpreting and predicting composition changes of atmospheric aerosols, it is indispensable to provide insight into the partitioning behaviors of SVOCs between condensed and gas phases. In this research, optical tweezers coupled with cavity-enhanced Raman spectroscopy were employed to observe the volatility of internally mixed citric acid (CA)/(NH4)2SO4 (AS) particles, and the effect of AS on the gas/particle partitioning behaviors of atmospheric organic acids was investigated. The radii and refractive indexes of the levitated droplets were determined in real time from the wavelength positions of simulated Raman spectra and the effective vapor pressures of CA at different relative humidities (RHs) were obtained according to Maxwell equation. For the CA/AS particle with organic to inorganic mole ratio (OIR) of 1:1, the effective vapor pressure of CA decreased with the decreasing of RH. When the RH decreased from 67% to 8.2%, the effective vapor pressure of CA decreased from (1.35±0.508)×10-4Pa to (3.0±1.0)×10-6Pa. Meanwhile, the CA/AS particles with OIR of 3:1, 1:3 were also studied, and the results show the same phenomenon compared to the particles with OIR of 1:1. When under constant RHs, the effective vapor pressures of CA decreased with the increasing of AS contents, suggesting that the presence of AS suppressed the partitioning of CA to aqueous particles. In addition, the mass transfer processes of water in CA and CA/AS/H2O systems were further studied. The characteristic time ratio between the droplet radius and RH was used to describe the water mass transfer difference dependent on RH. Compared to the characteristic time ratio of pure CA, the characteristic time ratio of CA/AS particles apparently increased. For CA/AS particles under the same RH steps, the characteristic time ratio increased with the AS content increase. According to the differential isotherm, the diffusion coefficients of citric acid and citric acid/ammonium sulfate at low RHs (RH ≈7%-1%, RH≈1%-7%) were calculated respectively. Generally, the key aspect of the current work was to deeply explore the relationship between the evaporation rates of SVOCs and water transport process.

更新日期：2019-10-12

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