Effects Of Fresh And Aged Sea Salt On The Chemistry Of Urban And Remote Regions

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It is now widely recognized that halogen atoms play a major role in tropospheric chemistry. However, models under-predict the concentrations of photochemically active precursors by at least an order of magnitude. This project is directed to resolving this discrepancy through a series of laboratory studies of the thermal and photochemical reactions of sea salt that have not before been investigated. The objectives are to: (1) measure chlorine (Cl2) production from reactions of salt mixtures representative of fresh and aged sea salt; (2) quantitatively assess the change in the photochemistry of sea salt particles as their chemical composition changes in a manner similar to that during transport in air; (3) elucidate the kinetics and mechanisms of oxidation of organics on sea salt "from the bottom up" by hydroxyl radicals generated in and on particles from nitrate and nitrite ion photochemistry. The intellectual merit lies in a deep understanding of sea salt chemistry that can be used in models of the marine boundary layer and other regions having suspended salt particles, and that will help to resolve the large discrepancies between measurements and model predictions of halogen atom precursors in the troposphere. This large disconnect is important to elucidate because tropospheric halogen chemistry impacts the formation and removal of O3, a toxic air pollutant, greenhouse gas and precursor to highly reactive OH radicals, as well as particle formation and growth that impacts public health, visibility and climate. The research will provide new insights into the importance and impacts of the photochemistry of the nitrate and nitrite anions which are incorporated into sea salt as it is transported in air, and into the impacts of organic coatings believed to exist on these particles. This research will also provide training to undergraduates, graduate students and postdoctoral scientists that is both broad in terms of atmospheric chemistry, yet deep in terms of the specific chemical knowledge that is developed and experimental experience gained.