Aircraft Observation of CO2, CO2 O3 and H2 over the North Pacific during the PACE-7 Campaign

Aircraft observation under the Pacific Atmospheric Chemistry Experiment (PACE) program was performed from February 13 to 21, 2000 to examine in detail the distributions of CO2 in the free troposphere between 5 and 11 km. Continuous measurements of CO2 mixing ratios were made using an on-board measuring system over the northern North Pacific between Nagoya, Japan and Anchorage, Alaska, and the western North Pacific between Nagoya and Saipan. Other trace gases, such as CO and O3, were also observed using continuous measuring systems at the same time. CO2 over the northern Pacific (35°N and higher) showed highly variable mixing ratios, ranging from 374 ppm in the upper troposphere to 366 ppm in the lowermost stratosphere. This highly variable distribution of CO2 was quite similar to that of CO, but the relationship between CO2 and O3 showed a strong negative correlation. These results indicated that the exchange process between the stratosphere and the troposphere significantly influences the large CO2variation. On the other hand, the CO2 over the western North Pacific to the south of Japan showed no significant variation in the upper troposphere at 11 km but a relatively larger variability at 5 km. The CO2 enhancement at lower altitudes coincided with the CO elevation due to the intrusion of a polluted air mass. Trajectory analysis indicated that the Asian continental outflow perturbed the CO2 distributions over the western Pacific. Very low mixing ratios of O3 of less than 20 ppb were distributed in the latitude band of 15–30°N at 11 km, reflecting the effects of transport from the equatorial region.