The physicochemical properties of particles affect many important atmospheric processes; yet, they are challenging to measure in situ. Herein, fluorescence aerosol flow tube (F-AFT) spectroscopy is applied to directly probe the ionic strength and pH in model systems of inorganic aerosol particles. The pH-sensitive probe molecule quinaldine red (QR) is incorporated into aerosol particles of sodium chloride, ammonium sulfate, ammonium bisulfate, and their mixtures. Fluorescence spectra are collected for variable particle acidity and ionic strength as mediated by composition and relative humidity. Results show that shifts in fluorescence wavelength are driven by changes in both ionic strength and pH. A two-dimensional regression analysis of the sulfate particle fluorescence line shape as a linear function of both molality and pH results in R² = 0.75. For comparison, R² values of 0.17 and 0.64 are found for molality and pH considered separately, respectively. The regression model calculated from the sulfate particle system did not fit the sodium chloride particle data well, suggesting that there are chemically specific effects governing the pH and ionic strength interactions with the dye molecule. Overall, these findings indicate the potential of F-AFT spectroscopy for in situ elucidation of the physicochemical properties of submicrometer aerosol particles, contingent upon a detailed understanding of the controlling factors in the fluorescence behavior of the chosen probe molecules in common aerosol particle-phase chemical environments.

中文翻译：

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喹哪啶红作为颗粒理化性质的荧光探针

颗粒物的物理化学性质影响许多重要的大气过程；然而，现场测量它们具有挑战性。在此，荧光气溶胶流管（F-AFT）光谱用于直接探测无机气溶胶颗粒模型系统中的离子强度和 pH 值。pH 敏感探针分子喹哪啶红 (QR) 被掺入氯化钠、硫酸铵、硫酸氢铵及其混合物的气溶胶颗粒中。收集由组成和相对湿度调节的可变颗粒酸度和离子强度的荧光光谱。结果表明，荧光波长的变化是由离子强度和 pH 值的变化驱动的。将硫酸盐颗粒荧光线形状作为摩尔浓度和 pH 值的线性函数进行二维回归分析，得出R ² = 0.75。为了进行比较，分别考虑摩尔浓度和 pH 值时，R ^{2值分别为 0.17 和 0.64。}从硫酸盐颗粒系统计算的回归模型与氯化钠颗粒数据不太吻合，这表明存在控制 pH 值和离子强度与染料分子相互作用的化学特异性效应。总体而言，这些发现表明 F-AFT 光谱在原位阐明亚微米气溶胶颗粒的物理化学性质方面具有潜力，这取决于对常见气溶胶颗粒相化学中所选探针分子荧光行为的控制因素的详细了解环境。