Convective Outflow From the U.S. to the Upper Troposphere Over the North Atlantic During the NASA INTEX-NA Airborne Campaign

A case study of rapid convective outflow from the U.S. was conducted using airborne measurements from flight 13 (July 28, 2004) of the NASA DC-8 during the Intercontinental Chemical Transport Experiment-North America (INTEX-NA). In the upper troposphere over the North Atlantic mixing ratios of CO and CH4 were elevated up to 134 and 1843 ppbv. In contrast, CO2 and OCS were reduced to 372.4 ppmv and 411 pptv respectively in the same flight regions. Overall, three regions at 8 - 11 km altitude were found to be impacted significantly by urban and industrial emissions. Here, we found good linear relationships between combustion related species such as CO, C2H2, and i-C5H12, with the urban/industrial tracers C2Cl4 and CHCl3. Moreover, the low mixing ratios and excellent correlation of OCS and CO2 indicated a signature of terrestrial uptake and minimal dilution of boundary layer air during rapid transport to the upper troposphere. Meteorological analysis, kinematic backward trajectories, and photochemical aging estimates using C3H8/C2H6 all pointed to the boundary layer over the southeastern U.S. as the source region. Halon-1211 mixing ratios exhibited no correlation or enhancement in the upper troposphere, suggesting a minimal contribution of Asian sources, in contrast to findings on other INTEX-NA flights. Our analysis indicates that convective activity over the southeastern U.S. was associated with a stationary front and strong winds ahead of the trough. The trajectories indicated that the air masses influencing the three regions meandered over the southeastern U.S. for several days prior to July 27. The air masses arriving in all three study regions were then transported over the Northeast and upward in fast zonal flow between the middle and upper troposphere on July 27-28. Moreover, flight regions sampled outside the three impacted regions also showed an excellent linear relationship between CO and CH4 and other urban tracers. This is a surprising result considering the diverse source regions indicated by our trajectory analysis. It appears that the entire tropospheric column over the North Atlantic during the time period surrounding flight 13 was impacted by North American anthropogenic emissions. Our analysis suggests that the troposphere over the mid-latitude North Atlantic basin was fumigated with U.S. pollutants in various stages of aging and demonstrates a pervasive impact of U.S. anthropogenic emissions on the mid-latitude troposphere over the North Atlantic.