Losses and transport of odd nitrogen species over the Western Atlantic Ocean during CASE/WATOX

Aircraft and shipboard measurements of mixing ratios for odd nitrogen species (N0y) were made over the western Atlantic Ocean during the summer of 1988. N0y in boundary layer air ranged from 4.8 ppbv near the U.S. east coast to 1.7 ppbv near a research ship 160 km from the coast. A vertical N0y gradient was observed near shore; mixing ratios decreased with altitude from 3.0 ppbv at 150 m to 1.3 ppbv at 2600 m. A smaller N0y gradient was observed near the ship, with mixing ratios also decreasing with altitude. During the observation period of this experiment, a high-pressure system over the mid-Atlantic limited advection of polluted continental air to a band just along the coast, thus preserving less polluted conditions to the east of the band. Loss rates for N0y advected from the continent, based on 3 eastward flights from the U.S. east coast, were estimated to be 2.0 ± 1.5% hour−1. Measurements near Bermuda were in marine air with average mixing ratios near the surface of 0.8 ppbv for NOy and 0.3 ppbv for total NO3 −. No significant vertical gradient was observed for NOy near Bermuda, where the high-altitude N0y mixing ratio was 0.7 ppbv. Overall, N0y mixing ratios near Bermuda were higher than would be expected on the basis of either measurements or computer modeling for remote marine air, suggesting possible influence from local anthropogenic sources.