Sodium nitrate particles: physical and chemical properties during hydration and dehydration, and implications for aged sea salt aerosols [An article from: Journal of Aerosol Science]

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Description:
Experiments probing the phase and behavior of NaNO"3 particles at different relative humidities, important for elucidating the role these particles play in the chemistry and radiative properties of marine regions, are presented. Changes in NaNO"3 particles during hydration were studied using environmental scanning electron microscopy (ESEM) and conventional SEM coupled with energy dispersive X-ray analysis (SEM/EDX). Mixtures of NaNO"3 and NaCl, which are typical of partially processed sea salt particles, were also studied. Complementary studies using long path FTIR were carried out to determine the extent of water association with NaNO"3 aerosols, and for comparison, NaCl, MgCl"2, and NH"4NO"3, as a function of relative humidity. The combination of these techniques shows that NaNO"3 particles exist as unusual metastable, amorphous solids at low relative humidity that undergo continuous hygroscopic growth with increasing relative humidity. While other evidence for this phenomenon has been reported, this is the first direct observation using ESEM.