Quantifying morphology and phase state of individual sea spray aerosol particles with atomic force microscopy and scanning electron microscopy

Aerosols are present in the atmosphere and can impact atmospheric properties that are responsible for Earth’s energy and water cycles. Aerosols can scatter incoming solar radiation either directly on the particles, or indirectly by acting as seed particles for cloud formation that then scatter incoming solar radiation. Currently, the combined effect is not well understood for aerosols in the atmosphere, specifically for sea spray aerosols, and there are large amounts of error associated with the measurements due to uncertainty in morphologies and physical phase states of the particles. As sea spray aerosols are produced, they vary in composition as a function of size from primarily organic to primarily salt due to mechanisms of generation. Therefore, information about the morphology and physical phase states must be determined. Nascent sea spray aerosols were imaged using scanning electron microscopy to determine morphology of aerosols. Additionally, aerosols were probed with an atomic force microscope to determine their physical phase state. It was found that at larger sizes, particles contain more salt leading to higher water uptake abilities while smaller aerosols contain more organic components leading to less water uptake abilities. Physical phase state of the smaller aerosols was determined to be solid or semi-solid indicating that the particles were viscous and water diffusion is limited to the surface leading to a decrease in cloud formation from these aerosols. Overall, clouds are more likely to be produced from larger particle sizes that will contribute more to the overall cooling effect of clouds on Earth’s atmosphere.