The Hydropathy Scale as a Gauge of Hygroscopicity in Sub-Micron Sodium Chloride-Amino Acid Aerosols

Abstract

Sodium chloride, NaCl, is commonly used as a proxy for sea spray aerosols. However, field work has demonstrated that sea spray aerosols also often contain a significant organic component. In this work, we examine the effect of amino acids on the hygroscopic properties of NaCl aerosols using a Fourier transform infrared spectrometer coupled to a flowcell apparatus. It is found that the effect can be drastically different depending on the nature of the amino acid. More hydrophilic amino acids such as glycine lead to continuous hygroscopic growth of internally mixed NaCl-amino acid aerosols generated from an equimolar precursor solution. However, more hydrophobic amino acids such as alanine do not significantly alter the hygroscopicity of NaCl aerosols. The hydropathy scale is found to be a good qualitative diagnostic for the effect that an amino acid will have on the hygroscopicity of NaCl.

Hygroscopicity of organic compounds as a function of organic functionality, water solubility, molecular weight, and oxidation level

“…3b) a continuous shrink in wet particle size was observed from 30 % to 80 % RH, and above 80 % RH the GFs increased slightly. Previous studies have reported that glycine particles started to absorb water above 60 % RH (Chan et al, 2005;Marsh et al, 2017;Darr et al, 2018) prior to deliquescence due to a capillary effect, which could be the potential reason for the shrinkage in their particle size in our study as a result of the microstructural rearrangement of particles upon humidification. The sizing of these structurally rearranged particles will be erroneous, especially at lower RH range, as the volume change of the particles upon wetting may be due not only to the water absorption but also the compaction of the original particles.…”

Hygroscopicity of Hofmeister Salts and Glycine Aerosols–Salt Specific Interactions

“…Herein, restudies are conducted to make a good comparison between mixed and pure components using the IR technique. As can be seen from the glycine aerosols in Figure S1, spectra of wet and dry glycine are taken from the highest and the lowest RHs, and the feature bands were assigned with the help of literature , (shown in Table S1). Two representative peaks at 928 and 895 cm –1 attributed to ρ-CH 2 and ν-CC appeared at 85.6% RH, respectively, and then shifted to 915 and 893 cm –1 at 6.3% RH.…”

“…16,17 In the amino acids, glycine is the smallest and simplest and has been found to be the most abundant in bioaerosols by Sun et al 18 with the identification in marine atmospheric aerosol samples. 19 A recent study observed dramatic effects of amino acids on the hygroscopic properties of inorganic aerosols, 20 leading to the modified CCN and physicochemical properties of atmospheric aerosols containing bioaerosols. 15,18,19,21,22 In our group's studies, the internally mixed glycine/NaNO 3 , glycine has been studied, and it was found that glycine promotes the crystallization of mixed droplets and inhibits the liquid−solid phase transition of inorganic salts.…”

“…During the chemical processes, hygroscopic properties play an important role in the kinetics and final components, so it has become a hot topic for researchers. , To date, the hygroscopic properties of major inorganic aerosols have been extensively studied, and several models, such as EAIM (extended aerosol inorganics model) and AIOMFAC (aerosol inorganic–organic mixtures functional groups activity coefficients), have been built to predict the hygroscopic growth factors of single salts and their mixtures. ,− Beside inorganics, second organic aerosols (SOAs), formed by the oxidation of volatile organic compounds, occupy 20–90% of the total PM2.5 (particulate matter with size of 2.5 μm) in urban pollution which has significant impact on the hygroscopic growth of PM2.5 , and has attracted much attention in the past decade. ,− Bioaerosol is one major type of atmospheric aerosol, where protein amino acids, as the most important one, can affect the atmospheric water cycle and cloud condensation activities of atmospheric aerosols. , In the amino acids, glycine is the smallest and simplest and has been found to be the most abundant in bioaerosols by Sun et al with the identification in marine atmospheric aerosol samples . A recent study observed dramatic effects of amino acids on the hygroscopic properties of inorganic aerosols, leading to the modified CCN and physicochemical properties of atmospheric aerosols containing bioaerosols. ,,,, In our group’s studies, the internally mixed glycine/NaNO 3 , glycine has been studied, and it was found that glycine promotes the crystallization of mixed droplets and inhibits the liquid–solid phase transition of inorganic salts. , …”

Comment on egusphere-2024-1254-Mehta

“…Moreover, composition of SSA vary with the seasons and biological activity (Parent et al, 2023). It has been shown to contain a significant organic component (Cavalli et al, 2004;Facchini et al, 2008), which has implications for its hygroscopicity and ice nucleation activity (Darr et al, 2018). Furthermore, SSA has been demonstrated to be geochemically important over geologic timeframes due to the presence of trace elements and metal pollution in aerosols derived from sea spray (Marx et al, 2014).…”