Date of Award

Winter 2010

Project Type

Dissertation

Program or Major

Earth and Environmental Science

Degree Name

Doctor of Philosophy

First Advisor

Robert Talbot

Abstract

The dissertation consists of two topics. The first was continental outflow from the U.S. to the North Atlantic with a case study of NASA DC-8 flight 13 during the Intercontinental Chemical Transport Experiment -- North America. This study found two interesting results. First, pollutants in the southeastern U.S. boundary layer were transported to the upper troposphere over the North Atlantic by vertical transport, which was facilitated by convection and warm conveyor belt uplifting combined with fast southwesterly flow in the free troposphere. Secondly, the data suggest that the total tropospheric column over the North Atlantic was impacted by U.S. outflow in various stages of photochemical aging. The second topic was a study of Mercury Depletion Events (MDEs) in the Arctic springtime and mercury chemical transformation in the northeastern U.S. MDEs were studied by simulations using a chemical box model and data analysis of NASA DC-8 flights during the Arctic Research of the Composition of the Troposphere from Aircraft and Satellites field campaign. A chemical box model was developed considering only gaseous reactions of mercury, halogens, and ozone chemistries. Several idealized sensitivity experiments based on data analysis were simulated to study what factors were most important to MDE formation. The box model captured similar patterns as the measurements which were high Br2, O3 depletion, and decline of ethyne and light weight alkanes inside the MDE areas. The simulations indicated that a continuous high Br2 mixing ratio, high intensity of solar radiation, and a high NOx regime caused faster Hg° depletion. Furthermore, the mercury diurnal cycle in the northeastern U.S. was studied with the box model and data analysis of year-round continuous measurements at the AIRMAP Thompson Farm site. The mass transport between gaseous-aqueous phases and aqueous reactions were added into the box model. Diurnal cycles of Hg° showed that it decreased ∼40 ppqv on stable nights. Box model simulations indicated that the decreased amount of Hg° was facilitated by water solubility of Hg° and uptake into the liquid water content of aerosols. Moreover, the sensitivity experiments with dry deposition added indicated that the ambient PHg level was strongly influenced by this process.

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