Marine/coastal boundary layer and vertical structure of ozone observed at a coastal site in Nova Scotia during the 1996 NARSTO-CE field campaign

Vertical profiles of ozone and meteorological parameters were analysed to investigate and characterise the vertical structure of a marine/coastal boundary layer and its impact on the transport affecting ground-level ozone in the Canadian southern Atlantic region. Most of the data used in this analysis are from a series of tethersonde measurements made at Chebogue Point, a small peninsula on the southwestern coast of Nova Scotia, in the summer of 1996 as part of the North American Research Strategy for Tropospheric Ozone – Canada East (NARSTO-CE) 1996 field campaign. The lowest 400 m of the atmosphere at this coastal site is dominated by stable thermal stability and is highly non-uniform in stratification. When flow is from the west, over cool marine waters of the Bay of Fundy/Gulf of Maine, a shallow (∼100 m) marine internal boundary layer is marked by very strong stable stratification and high humidity. The large gradient in sea surface temperature across the Gulf of Maine, from the US east coast to the west coast of Nova Scotia, seems to play an important role in delaying the onset of an equilibrium, neutrally stratified layer over the ocean surface and the development of the “low-level jet” that is frequently observed at this coastal site. The marine boundary layer is shown to have a significant impact on the ground-level ozone concentration observed near the coast as well as farther inland. Investigation of two high ozone episodes during the field campaign indicates that transport within the marine boundary layer played a critical role leading to the observed relatively high ground-level ozone concentrations in southern Nova Scotia.