Trace gas signatures of the airstreams within North Atlantic cyclones: Case studies from the North Atlantic Regional Experiment (NARE ’97) aircraft intensive

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This study reveals how airstreams within midlatitude cyclones draw and export trace gases from the polluted continental boundary layer, the midtroposphere, and the stratosphere of North America to the troposphere of the North Atlantic Ocean. The North Atlantic Regional Experiment (NARE) produced aircraft‐based trace gas measurements from eight midlatitude cyclones during the autumn of 1997. Meteorological and back trajectory analysis identified the various component airstreams of several cyclones, including a cold conveyor belt, two warm conveyor belts, a dry airstream, a previously undefined post cold front air‐stream, and a streamer fragment that originated in a dry airstream off the coast of California. O3, CO, and NOy mixing ratio distributions and relationships were determined for each airstream. Airstream chemical composition was related to the origin and transport history of the associated air mass. The lowest O3 values were associated with airstreams originating in Canada or the Atlantic Ocean marine boundary layer; the highest O3 values were associated with airstreams with a recent stratospheric component. The highest CO values were associated with lower tropospheric outflow from New England and a warm conveyor belt that advected boundary layer CO from the southeast United States to the mid and upper troposphere. The highest NOy values were also the result of lower troposphere polluted outflow from New England. Most NOy was removed from the airstreams that transported polluted boundary layer air to the free troposphere. A steep and positive O3/NOy slope was found for all airstreams in the free troposphere regardless of air mass origin.