Direct Determination of Aerosol pH: Size-Resolved Measurements of Submicrometer and Supermicrometer Aqueous Particles
Direct Determination of Aerosol pH: Size-Resolved Measurements of Submicrometer and Supermicrometer Aqueous Particles
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DOI：
10.1021/acs.analchem.8b00586
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发表时间：
2018-10-02
影响因子：
7.4
通讯作者：
Ault, Andrew P.
中科院分区：
文献类型：
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作者：
Craig, Rebecca L.;Peterson, Peter K.;Ault, Andrew P.
测量大气气溶胶的酸度是至关重要的，因为涉及气溶胶的许多关键多相化学反应高度依赖于pH。这些反应会影响影响气候和健康的二次有机气溶胶(SOA)形成等过程。然而，由于离子离子的非保守性，测定具有微小体积(10(-23)-10(-18)L)的大气颗粒物的PH值是一个分析挑战，特别是因为大多数化学气溶胶测量是在离线或真空下进行的，那里可能会失去水分，酸碱平衡发生变化。由于这些挑战，目前还没有探测大气气溶胶酸度的直接方法，pH值通常是通过离子平衡或热力学模型等替代/间接方法确定的。在这里，我们提出了一种新颖而简便的方法，通过对(NH_4)(2)SO_4-H_2SO_4水溶液气溶胶粒子撞击在pH指示剂纸上的手机图像的定量比色图像处理，直接测量从pH 0到4.5的尺寸分辨气溶胶酸度。观察到气溶胶酸度随着颗粒尺寸的减小而增加的趋势，这与单个颗粒pH的光谱测量是一致的。这些结果表明，直接测量大小分辨的大气气溶胶酸度是可能的，这是改善对依赖于pH的大气过程的基本理解所必需的，例如形成SOA。
Measuring the acidity of atmospheric aerosols is critical, as many key multiphase chemical reactions involving aerosols are highly pH-dependent. These reactions impact processes, such as secondary organic aerosol (SOA) formation, that impact climate and health. However, determining the pH of atmospheric particles, which have minute volumes (10(-23)-10(-18) L), is an analytical challenge due to the nonconservative nature of the hydronium ion, particularly as most chemical aerosol measurements are made offline or under vacuum, where water can be lost and acid-base equilibria shifted. Because of these challenges, there have been no direct methods to probe atmospheric aerosol acidity, and pH has typically been determined by proxy/indirect methods, such as ion balance, or thermodynamic models. Herein, we present a novel and facile method for direct measurement of size-resolved aerosol acidity from pH 0 to 4.5 using quantitative colorimetric image processing of cellular phone images of (NH4)(2)SO4-H2SO4 aqueous aerosol particles impacted onto pH-indicator paper. A trend of increasing aerosol acidity with decreasing particle size was observed that is consistent with spectroscopic measurements of individual particle pH. These results indicate the potential for direct measurements of size-resolved atmospheric aerosol acidity, which is needed to improve fundamental understanding of pH-dependent atmospheric processes, such as SOA formation.