Department of Chemistry and Biochemistry, University of Colorado Boulder , UCB 215, Boulder, Colorado 80309, United States.
CIRES, University of Colorado , UBC 216, Boulder, Colorado 80309, United States.
Environ Sci Technol. 2015 Oct 6;49(19):11500-8. doi: 10.1021/acs.est.5b02782. Epub 2015 Sep 22.
Knowledge about Setschenow salting constants, KS, the exponential dependence of Henry's Law coefficients on salt concentration, is of particular importance to predict secondary organic aerosol (SOA) formation from soluble species in atmospheric waters with high salt concentrations, such as aerosols. We have measured KS of glyoxal and methylglyoxal for the atmospherically relevant salts (NH4)2SO4, NH4NO3, NaNO3, and NaCl and find that glyoxal consistently "salts-in" (KS of -0.16, -0.06, -0.065, -0.1 molality(-1), respectively) while methylglyoxal "salts-out" (KS of +0.16, +0.075, +0.02, +0.06 molality(-1)). We show that KS values for different salts are additive and present an equation for use in atmospheric models. Additionally, we have performed a series of quantum chemical calculations to determine the interactions between glyoxal/methylglyoxal monohydrate with Cl(-), NO3(-), SO4(2-), Na(+), and NH4(+) and find Gibbs free energies of water displacement of -10.9, -22.0, -22.9, 2.09, and 1.2 kJ/mol for glyoxal monohydrate and -3.1, -10.3, -7.91, 6.11, and 1.6 kJ/mol for methylglyoxal monohydrate with uncertainties of 8 kJ/mol. The quantum chemical calculations support that SO4(2-), NO3(-), and Cl(-) modify partitioning, while cations do not. Other factors such as ion charge or partitioning volume effects likely need to be considered to fully explain salting effects.
关于 Setschenow 盐化常数（KS）的知识，亨利定律系数对盐浓度的指数依赖性，对于预测大气水中高盐浓度（如气溶胶）可溶性物质形成二次有机气溶胶（SOA）特别重要。我们已经测量了大气相关盐（（NH4）2SO4、NH4NO3、NaNO3 和 NaCl）中乙二醛和甲基乙二醛的 KS 值，发现乙二醛一致地“盐化”（KS 值分别为-0.16、-0.06、-0.065 和-0.1 毫摩尔/（-1）），而甲基乙二醛“盐析”（KS 值分别为+0.16、+0.075、+0.02 和+0.06 毫摩尔/（-1））。我们表明，不同盐的 KS 值是可加的，并提出了一个用于大气模型的方程。此外，我们还进行了一系列量子化学计算，以确定乙二醛/甲基乙二醛一水合物与 Cl(-)、NO3(-)、SO4(2-)、Na(+)和 NH4(+)之间的相互作用，并发现乙二醛一水合物的水置换吉布斯自由能为-10.9、-22.0、-22.9、2.09 和 1.2 kJ/mol，而甲基乙二醛一水合物的水置换吉布斯自由能为-3.1、-10.3、-7.91、6.11 和 1.6 kJ/mol，不确定度为 8 kJ/mol。量子化学计算支持 SO4(2-)、NO3(-) 和 Cl(-) 会改变分配，而阳离子则不会。可能需要考虑其他因素，如离子电荷或分配体积效应，以充分解释盐化效应。
