AASE‐II Observations of trace carbon species distributions in the mid to upper troposphere

We report tropospheric (altitudes > 5 km) observations of CO 2 , CO, CH 4 , and light hydrocarbons (C 2 ‐ C 4 ) over the latitude range from 90°N to 23°S recorded onboard the NASA DC‐8 aircraft during the winter 1992 Second Airborne Arctic Stratospheric Expedition (AASE‐II). Mixing ratios for these species exhibited significant north‐south gradients with maximum values in subpolar and arctic regions and minima over the southern tropics. At latitudes > 40°N, the mixing ratios of most species increased significantly over the course of the 3‐month measurement period. Also at high northern latitudes, the variations of all relatively long‐lived reactive carbon species were linearly correlated with fluctuations of CO 2 with CO, CH 4 , C 2 H 6 , C 2 H 2 , C 3 H 8 , and n‐C 4 H 10 exhibiting average enhancement ratios in terms of ppbV(X)/ppmv(CO 2 ) of 13.8, 8.4, 0.21, 0.075, 0.085, and 0.037, respectively.