TY - JOUR
T1 - Multistep Phase Transitions in Sea Surface Microlayer Droplets and Aerosol Mimics using Microfluidic Wells
AU - Nandy, Lucy
AU - Liu, Shihao
AU - Gunsbury, Connor
AU - Wang, Xiaofei
AU - Pendergraft, Matthew A.
AU - Prather, Kimberly A.
AU - Dutcher, Cari S
N1 - Publisher Copyright:
Copyright © 2019 American Chemical Society.
PY - 2019/7/18
Y1 - 2019/7/18
N2 - Oceanic sea spray is one of the largest contributors of atmospheric aerosol particles worldwide. The phase of aerosol particles is known to impact radiative forcing and cloud nucleation. However, as chemically complex aqueous systems that include mixtures of biological, organic, and salt constituents, it is a challenge to predict the phase of sea spray aerosol especially as they age in the atmosphere. In this study, phase behavior (liquid-liquid phase separation, LLPS, and crystallization) of sea surface microlayer (SSML) sample and chemical mimics are investigated using a microfluidic pervaporation approach. Internally mixed aqueous droplets with varying compositions and concentrations are trapped in microfluidic wells, and phase transitions of the droplets are optically determined in a slow dehydration process. A system containing SSML sample combined with an organic acid 3-methyl glutaric acid (3-MGA) undergoes multiple phase changes, including two crystallization and two LLPS events. The added organic acid increases the sample's organic-to-inorganic ratio and moves the system into the range typical of aged SSA. To better understand the contributing constituents to the observed phase changes, control experiments with inorganic salt components NaCl, MgCl2, and Na2SO4 are performed with and without 3-MGA, at varying organic to inorganic ratios. 3-MGA leads to LLPS, and the presence of Mg2+ more readily facilitates LLPS than Na+. With the systems studied, LLPS is more prevalent for the chemical mixtures in an intermediate OIR range. This study provides new insight into sea spray aerosol phase as a function of composition and relative humidity and demonstrates multistep phase transitions for these complex systems.
AB - Oceanic sea spray is one of the largest contributors of atmospheric aerosol particles worldwide. The phase of aerosol particles is known to impact radiative forcing and cloud nucleation. However, as chemically complex aqueous systems that include mixtures of biological, organic, and salt constituents, it is a challenge to predict the phase of sea spray aerosol especially as they age in the atmosphere. In this study, phase behavior (liquid-liquid phase separation, LLPS, and crystallization) of sea surface microlayer (SSML) sample and chemical mimics are investigated using a microfluidic pervaporation approach. Internally mixed aqueous droplets with varying compositions and concentrations are trapped in microfluidic wells, and phase transitions of the droplets are optically determined in a slow dehydration process. A system containing SSML sample combined with an organic acid 3-methyl glutaric acid (3-MGA) undergoes multiple phase changes, including two crystallization and two LLPS events. The added organic acid increases the sample's organic-to-inorganic ratio and moves the system into the range typical of aged SSA. To better understand the contributing constituents to the observed phase changes, control experiments with inorganic salt components NaCl, MgCl2, and Na2SO4 are performed with and without 3-MGA, at varying organic to inorganic ratios. 3-MGA leads to LLPS, and the presence of Mg2+ more readily facilitates LLPS than Na+. With the systems studied, LLPS is more prevalent for the chemical mixtures in an intermediate OIR range. This study provides new insight into sea spray aerosol phase as a function of composition and relative humidity and demonstrates multistep phase transitions for these complex systems.
KW - atmospheric aerosols
KW - crystallization
KW - droplet microfluidics
KW - liquid-liquid phase separation
KW - organic material
KW - sea spray aerosols
KW - sea surface microlayer
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U2 - 10.1021/acsearthspacechem.9b00121
DO - 10.1021/acsearthspacechem.9b00121
M3 - Article
AN - SCOPUS:85069630533
SN - 2472-3452
VL - 3
SP - 1260
EP - 1267
JO - ACS Earth and Space Chemistry
JF - ACS Earth and Space Chemistry
IS - 7
ER -