Date Awarded


Document Type


Degree Name

Doctor of Philosophy (Ph.D.)


Virginia Institute of Marine Science


Rebecca M. Dickhut


Gaseous fluxes of polycyclic aromatic hydrocarbons (PAHs) across the air-water interface of Southern Chesapeake Bay were calculated for the period January 1994 through May 1995 using a modified two-film model. Additionally, the distributions of PAHs between the vapor and aerosol phase in the atmosphere, and between the freely dissolved and suspended particulate phase in the water column were investigated. Net instantaneous gaseous fluxes of PAHs were determined to vary in direction and magnitude both spatially and temporally across the air-water interface of Southern Chesapeake Bay at four sites ranging from remote to urban and highly industrialized. The magnitude of gas exchange fluxes was of the same order as wet and dry atmospheric depositional fluxes. Spatial variations in gaseous fluxes resulted from differences in the air-water concentration gradients between sites. Temporal variations in gas exchange fluxes resulted from seasonal changes in both water temperatures and vapor concentrations. Atmospheric PAH vapor concentrations increased exponentially with temperature at the non-rural sites suggesting volatilization from contaminated surfaces (soils, roads, vegetation) during warmer weather; whereas, PAH vapor concentrations at the rural site decreased with time. All sites experienced increased loadings of particulate-associated PAHs during winter. Mean total atmospheric PAH concentrations ranged from 7.87 ng/m&\sp3& at a rural (Haven Beach) site to 92.8 ng/m&\sp3& at an urban (Elizabeth River) site. Plots of the logarithm of the particle-vapor partitioning coefficient (C&\rm\sb{lcub}p{rcub}/TSP\sp\* C\sb{lcub}v{rcub})& versus inverse temperature indicate different particle characteristics or atmospheric partitioning processes at the urban and rural sites. Three methods (gas sparging, semipermeable membrane devices, filtration with sorption of the dissolved contaminant fraction to XAD-2 resin) for determining freely dissolved contaminant concentrations in estuarine waters were investigated. Mean total PAH concentrations in surface waters ranged from 24.2 ng/l at a mainstem bay site to 91.1 ng/l at the industrialized Elizabeth River site. Dissolved-particulate partitioning of PAHs approximated equilibrium theory at all sites and sampling periods. The results of this study support the hypothesis that gas exchange is a major transport process affecting concentrations and exposure levels of PAHs in the southern Chesapeake Bay Region.



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