Sea spray aerosol composition, pH and structure

Sea spray aerosol (SSA) is a major component of natural aerosols, yet the composition, structure, and pH of SSA are poorly constrained. Research efforts in the Grassian lab are tackling all three parameters:

• Morphology, phase, and chemical composition are vital links to understanding the impacts of aerosol particles in the atmosphere, and there is a need for detailed studies of individual particles under realistic atmospheric conditions. Chemical and physical analyses using high-resolution spectro-microscopics probe are being conducted to provide insight on aerosol composition and morphologies on size scales relevant to capturing these heterogeneities. To probe the dynamic chemical composition of SSA, we are also conducting surface measurements at the air/water interface on model SSA in tandem with theoretical work by collaborators in the Amaro group. We are working on identifying what the surface of simulated model SSA looks like, and how the organics and inorganics are segregated on the surface.

• Aerosol pH is a critical parameter controlling the impact of aerosols on human health and cloud formation, yet is difficult to measure due to the tiny volumes (femtoliter to picoliter) of typical atmospheric aerosols and the measurement challenges of precisely detecting hydronium ions. We developed a colorimetric method using pH paper to quantify the pH of size-separated SSAs that accounts for the elevated levels of salt they contain. We found that SSA are rapidly acidified from the pH of the ocean (ca. 8) to much lower levels (pH 2-4) within minutes after their generation from crashing waves. Ongoing work in our group is targeted at determining how fatty acids, amino acids, and acidic atmospheric gases play roles in this rapid acidification.