Flight 12: Hong Kong Local 4  

The P-3B took a track heading north to the east of Taiwan along 124.5E. This track was selected to attempt to sample a stratospheric intrusion expected just north of 26N.  Returning to Hong Kong a short leg of high altitude sampling into the South China Sea was planned to look for potential biomass burning outflow.  

Results:  A layer of elevated CO and NOy was observed on the initial ascent between 7 and 10Kft.  This layer was not present on the initial descent about 1 hour later.  As in previous flights to the east and north, boundary layer legs were characterized by high variability in NO, NOy, SO₂, and CN suggestive of shipping lanes.  Numerous ship sightings were also reported from the cockpit.  An uncooperative air traffic control representative prevented sampling of the expected stratospheric intrusion by forcing the P-3B to stay below 7.5Kft north of 26N.  On reaching the South China Sea, conditions were fairly clean up to 20Kft with CO decreasing with altitude. Between 20-24Kft, a few thin layers were observed with elevated CO, NO, NOy, O₃, and CN.  Although not dramatic, CO at 24Kft was higher than that at 20Kft.  Another layer at 22Kft contained enhanced O₃ and NOy which were anticorrelated with dew point.