Mixing of anthropogenic pollution with stratospheric ozone: A case study from the North Atlantic wintertime troposphere

As part of the North Atlantic Regional Experiment (NARE), instrumentation f or the measurement of O-3 and CO was included on research flights conducted by the National Oceanic and Atmospheric Administration WP-3D Orion aircraf t from St. John' s, Newfoundland, Canada, and Keflavik, Iceland, from Febru ary 2 to 25, 1999. These flights sampled the lower troposphere over the wes tern North Atlantic Ocean. One significant feature observed during these fl ights was the close proximity of air masses with contrasting source signatu res: high levels of anthropogenic pollution immediately adjacent to elevate d O-3, of stratospheric origin. Here we present a case study showing the mo st pronounced example of this proximity, which was associated with a fronta l passage across North America and out into the North Atlantic region. Traj ectory analyses and satellite imagery are used to investigate the transport mechanisms that create the interleaving of air masses from the different s ources. One important chemical feature was noted: in air masses with differ ing amounts of anthropogenic pollution admired, O-3, was negatively correla ted with CO, which indicates that emissions from surface anthropogenic sour ces had reduced O-3, in this wintertime period, even in air masses transpor ted into the free troposphere.