Marine atmospheric influences on trace gas observations and transport during the ICARTT 2004 campaign
The transport of pollutant trace gases and aerosols above coastal waters is of eminent importance to air quality and global climate processes. The research presented in this dissertation is a two-part investigation of this transport as observed during the ICARTT campaign, with focus devoted to the transit and evolution of trace gases in the lower marine atmosphere above the Gulf of Maine (GOM) and western North Atlantic Ocean. Part I advances a quasi-lagrangian case study of a plume emanating from the New York City source region. In this, analysis of airborne intercepts of the plume captured its transformation from a polluted airmass within a residual layer, to a well defined flow maintained within a stable internal boundary layer (SIBL). The SIBL was defined by sharp gradients in moisture, temperature and wind speed, and persisted throughout the NYC plume's transit. Further investigation showed that the SIBL measurably influenced trace gas variability and evolution. Despite its low altitude, the SIBL strongly inhibited surface interactions, thus limiting removal processes. Pronounced vertical shear in wind speed generated frequent instances of Kelvin-Helmholtz instability and turbulence within the plume layer. This resulted in a high degree of spatial variability in mixing ratios observed within the plume, enhanced mixing, and contributions to its overall transit. Surface observations during the plume passage recorded pollutant mixing ratios equaling the most extreme measured that summer, a fact that motivated the further investigation of the SIBL pursued in Part II. In this, an extended analysis of the coastal SIBL was presented in the context of the entire campaign period. The SIBL was detected in the majority of low-altitude flights over the GOM, with its thickness varying significantly with fetch during the day and to a lesser extent at night. Nocturnal observations revealed the periodic detection of a low level jet within the SIBL. Overall, SIBL heights for both time period were higher than the predicted values determined from SIBL relationships established in related studies, suggesting that additional parameters like turbulent fluxes or surface roughness are required to determine SIBL development in the region.
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