Download or read book Chemical Characterization of Heterogeneous Ice Nuclei in the Atmosphere written by Sarah Sihvonen and published by . This book was released on 2016 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Aerosol particles impact the climate by serving as the seeds to form water droplets and ice to form clouds. However, these aerosol-cloud interactions are the least understood aspect of our understanding of the climate system. Mineral dust aerosol is the largest global source of ice nucleating particles. During atmospheric transport, mineral dust can be exposed to sulfuric acid, which has been shown to decrease the ice nucleation activity of these particles. Many explanations for this observation, such as chemical changes to the surface or product formation that blocks active sites, have been suggested. Our research focused on building a molecular picture of these surfaces to understand why sulfuric acid exposure reduces the ice nucleation activity of clay minerals such as kaolinite. We performed studies using X-ray diffraction and solid state NMR that investigate the changes that clay minerals undergo as a result of acid exposure. We are the first to show that the formation of a product on the surface of kaolinite was responsible for the decreased ice nucleation activity, not surface changes to the mineral itself. We continued to study aerosol-cloud interactions by using parcel models that explore the impact of ice growth surface kinetics on the competition between heterogeneous and homogeneous ice nucleation in clouds. We found that impaired growth of ice favors homogeneous freezing. The parcel models will be expanded to include our work on clay minerals to explore the impact of chemical aging of ice nuclei on overall cloud properties. We also studied the effect of acidic-processing on coal fly ash samples. Coal fly ash has been found to have a similar atmospheric impact as mineral dust, but is studied to a lesser extent. Like mineral dust, coal fly ash can serve as a source of bioavailable iron to phytoplankton in nutrient limited regions of the ocean. Fly ash has also been found to serve as an ice nucleating material. We performed aqueous sulfuric acid-treatment on fly ash samples representative of the types produced in the United States. We found that a soluble salt, gypsum (hydrated calcium sulfate), formed on three out of four samples. The most iron rich sample did not react with sulfuric acid. However, acidic-processing was shown to increase the amount of soluble iron which has implications for the biogeochemical cycle. These results also demonstrate that further work investigating these fly ash systems is warranted. In addition to our work on ice nucleation, we constructed a photoacoustic spectrometer to measure the absorbance of aerosol particles to study the optical properties of atmospheric aerosol. These measurements will aid in understanding the interactions of aerosol particles with light and the radiative balance of the planet.