The impact of primary marine aerosol on atmospheric chemistry, radiation and climate

This dissertation examined the influence of marine aerosol cycling on atmospheric chemistry, physics and radiation. Measurements indicate that marine aerosols and the production and cycling of halogens are important influence on climate. A capacity to examine marine aerosol cycling in the global atmospheric system requires that chemistry be treated explicitly. Multiphase chemistry is sensitive to the initial conditions and the solution method. This study examined this sensitivity: Laboratory measurements of fresh, unreacted marine aerosol were used to formulate a marine aerosol source parameterization that captured the initial conditions of the aerosol population. A chemical mechanism was benchmarked across a set of observed conditions in the marine atmosphere. The mechanism was reduced to maximize computational speed. Finally, the mechanism was coupled to the NCAR Community Atmosphere Model (CAM). Decadal simulations with CAM were run with and without reactive-halogen chemistry and with and without treatment of particulate organic carbon in the marine aerosol source function. Results were interpreted (1) to evaluate influences of marine aerosol production on the properties of aerosol populations and clouds over the ocean and effects on radiative transfer, (2) atmospheric burdens of halogen species and their impacts on O3, NOx, OH, DMS, and particulate non-sea-salt SO42−, and (3) the global production and influences of marine-derived particulate organic carbon. The model reproduced major characteristics of the aerosol system and demonstrated a sensitivity of climate to marine-derived components in Earth’s troposphere. Statistically significant changes in aerosol optical properties were observed based on changes to the marine aerosol source function, and due to multiphase chemistry. No significant changes in large-scale circulation or top-of-atmosphere radiative budgets were observed, due to the use of an offline ocean surface, and short duration of the simulations. Computational resources were the limiting factor preventing analysis of the impact the system might have on radiative transfer and climate. The capacity to address global-scale multiphase chemistry questions is a major advancement that this research provides, but results are preliminary. While it is implied that the physical and chemical implications of marine aerosol cycling are globally relevant, gaps in our understanding exist. Combined observations with refined simulation tools are necessary.