By the wind-driven action on the ocean surface, sea spray aerosols (SSAs) that are ejected into the atmosphere become coated with organic molecules found in the sea surface microlayer (SSML). These coatings play important roles in atmospheric chemistry as they affect the size, lifetime, reactivity, and ice nucleating abilities of aerosols. Model systems consisting of dipalmitoylphosphatidic acid (DPPA) and palmitic acid (PA) were studied by surface tensiometry and Brewster angle microscopy (BAM) in terms of their relaxation behaviors. Relaxation experiments were conducted using two methodologies: constant surface pressure to measure changes in area with time, and constant area to track how surface pressure changes with time. While held at a constant surface pressure of 30 mN/m, it was found that PA exhibited a collapse-type relaxation mechanism, which can be fit to the Vollhardt model of nucleation and growth, whereas DPPA only experiences what is attributed to structural reorganization. Mixed monolayer systems of DPPA and PA adopt the same relaxation behavior as DPPA thus indicating that this phospholipid is the dominant component in determining the relaxation mechanism of the mixed monolayers. Constant area experiments show evidence of phase changes in the monolayer over time. The relaxation mechanism of PA is further investigated by altering the headgroup of the monolayer as well as the subphase upon which it is spread to further elucidate the factors which govern its relaxation behavior at the air/aqueous interface.

Relaxation mechanisms of model sea spray aerosols

251st National Meeting (2016)

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