| Although critical to an understanding of global tropospheric ozone levels and atmospheric photochemical cycles, few reactive nitrogen oxides measurements have been made within the remote atmosphere. As a result, the influence of transport of anthropogenic emissions on reactive nitrogen oxides and O 3 levels in the global atmosphere is poorly known. In order to address these deficiencies, NO and NOy (total reactive nitrogen oxides) were determined at Terceira in the Azores Islands in the summer of 1993 and NO, NO2, and NOy were determined at the northern tip of Newfoundland in late winter---early spring of 1996.; In the first study, analyses of back-trajectories and low levels of NO y (median mixing ratio of 73 pptv) indicate that the troposphere adjacent to the ocean (the marine boundary layer, or MBL) over the central North Atlantic during August 1993 was not influenced by direct transport of anthropogenic emissions. Instead, indirect transport via subsidence of air from aloft appears to dominate this region during summer. A simple model of this process was developed and used with measurements of NOy levels to find that NOy is lost rapidly in the MBL, decreasing by 63% in ∼1.2 days in the absence of downward transport of NOy. As a result, transport of elevated levels of NOy which occurs aloft may be detected quickly at the surface. In contrast, CO and O3 are removed from the MBL much more slowly than NOy, and thus levels of CO and O3 within the MBL change at a slower rate. Thus, initial correlations of NOy, CO, and O3 within the FT will be degraded within the MBL. This is significant as these correlations are commonly used to estimate the amount of ozone photochemical production resulting from transport of anthropogenic emissions.; In the second study, back-trajectories and NOx measurements are used to show that average NOx levels are 30 pptv in air flows from the ocean, are 23 pptv in air flows from the Arctic and subarctic, and are 68 pptv in air flows from northeastern portions of North America which travel to northern Newfoundland during late winter---early spring of 1996. Previous studies indicate the O3 photochemical production is negative or near zero during the spring over the northern North Atlantic at these NOx levels. However, modeling performed here indicates that warming of Arctic and subarctic air flows during advection over the ocean results in enhanced peroxyacetyl nitrate (PAN) decomposition and maximum NOx levels of ∼70 pptv. Due to the direct relationship between O3 photochemical production and NOx level, increases in MBL NOx levels resulting from advection of air flows from the Arctic and subarctic and from northeastern portions of North America over the northwestern North Atlantic yield an estimated increase in O3 photochemical production of 0.2--1.2 ppbv/day. This represents between 6% and 400% of the rate that O3 is removed at the ocean surface in this region, and thus may have a significant impact on the O3 budget within the MBL over the northwestern North Atlantic during late winter---early spring. |
