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 i nvestigate and characterise the Vertical structure of a marine/coastal boun dary layer and its impact on the transport affecting ground-level ozone in the Canadian southern Atlantic region. Most of the data used in this analys is 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 atm osphere at this coastal site is dominated by stable thermal stability and i s highly non-uniform in stratification. When flow is from the west, over co ol marine waters of the Bay of Fundy/Gulf of Maine, a shallow (similar to 1 00 m) marine internal boundary layer is marked by very strong stable strati fication and high humidity. The large gradient in sea surface temperature a cross the Gulf of Maine, from the US east coast to the west coast of Nova S cotia, seems to play an important role in delaying the onset of an equilibr ium, neutrally stratified layer over the ocean surface and the development of the "low-level jet" that is frequently observed at this coastal site. Th e marine boundary layer is shown to have a significant impact on the ground -level ozone concentration observed near the coast as well as farther inlan d. Investigation of two high ozone episodes during the field campaign indic ates 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. (C) 2000 Published by Elsevier Science Ltd.