Meteorological mechanisms for transporting O3 over the western North Atlantic Ocean: A case study for August 24-29, 1993

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A large-scale view of O3 transport over the western North Atlantic Ocean (WNAO) in summer illustrates distinct sources of O3, and separate transport mechanisms are important at different vertical levels in the troposphere. The week-long period presented covers a sequence of O3 sondes released from Bermuda and encompasses two surface O3 events in the month-long NARE intensive. O3 and CO peaked at Chebogue Point on the evening of August 25 and after midnight on the morning of August 28. At Sable Island, peaks occurred during early morning of August 26 and late morning of August 28. These events occurred under W-SW winds associated with advancing low-pressure systems that transported anthropogenic pollutants over the WNAO. The concentrations dropped with the passage of a trough or a cold front. Evidence suggests the surface was occasionally isolated from polluted air during favorable transport with pollutants lifted in warm sector flow riding over a wedge of cool, thermodynamically stable air. In addition to surface O3, the O3-sonde profile over Bermuda on the morning of August 27 showed a deep layer of O3 from 6 to 12 km. Using back trajectories and two tracers (isentropic potential vorticity and water vapor), we illustrate that stratospheric ozone exchanged into the upper troposphere in conjunction with surface cyclogenesis was advected through the middle to upper troposphere over the midlatitudes with the potential to reach lower altitudes through subsidence in regions of anticyclonic motion.

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Journal of Geophysical Research Atmospheres