Aircraft Observation of CO2, CO, 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 CO 2 in the free troposphere between 5 and 11 km. Continuous measurements of CO 2 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 O 3 , were also observed using continuous measuring systems at the same time. CO 2 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 CO 2 was quite similar to that of CO, but the relationship between CO 2 and O 3 showed a strong negative correlation. These results indicated that the exchange process between the stratosphere and the troposphere significantly influences the large CO 2 variation. On the other hand, the CO 2 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 CO 2 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 CO 2 distributions over the western Pacific. Very low mixing ratios of O 3 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. DOI: 10.1111/j.1600-0889.2004.00088.x