MEASUREMENT OF O-3 AND RELATED-COMPOUNDS OVER SOUTHERN NOVA-SCOTIA .1. VERTICAL DISTRIBUTIONS

As part of the North Atlantic Regional Experiment, the National Resear ch Council of Canada Twin Otter aircraft was used to measure the conce ntration of O-3 and related compounds in the atmosphere over southern Nova Scotia. Forty-eight flights were conducted, primarily over the su rface sampling site in Chebogue Point, Nova Scotia, or over the adjoin ing Atlantic Ocean. A typical flight included one or more vertical pro files from 30 m above the surface to an altitude of 3 or 5 km. We pres ent here O-3 measurements and supporting chemical and meteorological d ata including NOy, CO, accumulation mode aerosol particles, winds, tem perature, and dew point. Data are presented in a format which illustra tes day-to-day variability and vertical structure; We find that Nova S cotia is impacted by a wide variety of air masses with varying chemica l content depending on flow conditions relative to the locations of up wind emission regions. As an aid to understanding the chemical composi tion of the air, we characterize four types of events: (1) moist conti nental boundary layer air with high concentrations of O-3 and other an thropogenic pollutants which is advected to Nova Scotia in relatively thin vertical layers, usually with a base altitude of several hundred meters; (2) ''background'' air with concentrations of anthropogenic in gredients much lower than experienced in continental pollution episode s but higher than observed in more remote regions of Canada, suggestin g a dilute anthropogenic or biomass burning influence; (3) near-surfac e air which because of a strong temperature inversion over the Atlanti c Ocean, is decoupled from air aloft, with the consequence that near-s urface measurements do not give a representative view of the eastward transport of the North American plume; and (4) dry air masses with hig h O, concentration in which we have to distinguish between boundary la yer and upper atmosphere source regions.