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Investigating the impacts of aerosol sources upon coastal clouds


Aerosols can affect climate and precipitation through their ability to serve as cloud seeds. Of particular interest to this dissertation are the sources of aerosols impacting storms that cross the coast of California. Ice nucleating particles (INPs) are particles capable of triggering heterogeneous ice formation in the atmosphere. Even though they are rare, they can have an outsized effect due to their ability to trigger cloud glaciation even at low concentrations. In this dissertation, the effect of aerosol sources and microphysical properties, particularly those of INPs, upon coastal clouds are studied using a combination of lab experiments, field measurements, remote sensing, and atmospheric modeling. Measurements of ambient particles showed that specific meteorological conditions can lead to the transport of anthropogenic pollution particles to the coast of California from the Central Valley, potentially modifying properties of coastal clouds. The role of meteorological conditions in dictating particle source during a winter storm was also investigated by analyzing precipitation samples and remote sensing of clouds. The features of single particle mass spectrometer measurements of dust and bioparticles are explored and characterized. The findings from these lab experiments are used to develop a novel decision tree for the identification of bioparticles in ambient measurements. For the first time, single particle measurements of marine and coastal INP composition were performed. The major source of INPs active at T = -30 ºC was dust, while sea spray aerosol (SSA) and bioparticles were minor sources. SSA that activated into ice crystals were found to be enriched in organics. A novel methodology was developed to estimate INP sources without using direct measurements of INPs. Bioparticles are found to dominate INPs active at T = -20 ºC. Finally, a series of experiments showed that dust can be resuspended from the ocean and still be able to nucleate ice. Aerosol transport simulations of this phenomenon showed that this process may be important for INP populations in the Southern Ocean.

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