Marine Organic Aerosols and Their Implication to Climate

GANTT, BRETT DANIEL. Marine Organic Aerosols and Their Implication to Climate. (Under the direction of Nicholas Meskhidze.) Despite the fact that marine organic aerosols have been hypothesized to affect climate through their impact on cloud microphysical properties, emission parameterizations have only recently been available and have not undergone extensive model evaluation. In a literature review of the chemical and physical characteristics of marine organic aerosols, recent trends indicate that these aerosols are externally-mixed with sea-salt and can influence the size distribution towards larger and more numerous particles. Simulations of the emission of secondary and primary marine organic aerosols are performed using the Community Multiscale Air Quality (CMAQ) version 4.7 model, with primary organic aerosols (POA) having a much larger effect on surface aerosol mass concentrations. To develop an improved marine primary organic aerosol emission parameterization, observations of organic mass fraction of sea spray aerosol (OMSSA), chlorophyll-a concentration ([Chl-a]), and 10 meter wind speed (U10) at two coastal sites are used to multivariable size-resolved parameterization that has global emissions of 2.8 to 5.6 Tg C yr −1 whose seasonality is more consistent with observations. These emissions, as well as several previously published marine POA emission parameterizations, are evaluated within the GEOS-Chem modeling framework. From this evaluation, marine POA emissions directly related to [Chl-a] best predicted the seasonality of surface concentrations while no parameterization performed well predicting episodic events. The climate impact of marine organic aerosols is determined by implementation of their emissions into the Community Atmosphere Model version 5 (CAM5) with aerosol microphysics. The combination of marine secondary organic aerosols, methane sulfonate, and primary organic aerosol contribute up to 400 ng m -3 in annual average submicron organic aerosol mass concentration. Compared to the simulations without marine organic aerosols, the simulations with externally-mixed marine POA emissions have a 20% increase in the surface cloud condensation nuclei (CCN) concentration near biologically productive ocean regions. The simulations only including secondary marine organic aerosol sources or internally-mixed marine POA emissions did not have large differences in the surface CCN concentration relative to the simulations with marine organic aerosols. Model simulations with and without marine organic aerosol and anthropogenic emissions are compared to determine the impact of marine organic aerosols on the current and preindustrial climate. Marine organic aerosols increase the model-predicted aerosol indirect forcing estimate by ~0.1 W m -2 mainly due to changes in cloud microphysical properties in the pristine preindustrial climate. Marine Organic Aerosols and Their Implication to Climate by Brett Daniel Gantt A dissertation submitted to the Graduate Faculty of North Carolina State University in partial fulfillment of the requirements for the degree of Doctor of Philosophy Marine, Earth, and Atmospheric Sciences Raleigh, North Carolina