Note that water vapor is essentially at zero concentration above the tropopause, which is at most 16 km high (it varies with latitude and season) because it is too cold for water to survive as gas, or even as liquid. In contrast, direct measurements have shown that CO2 persists, and even varies with concentrations at lower altitudes. See
figures below.
(Click on image for larger graphic.)
(Click on image for larger graphic.)
(Updated 7th May 2021)
ecoquant
HOW DOES THE CO2 CONCENTRATION VARY VERTICALLY ACROSS THE TROPOSPHERE FROM MID TROPOSPHERE TO TROPOPAUSE?
THANKS
Abshire, James B., Anand Ramanathan, Haris Riris, Jianping Mao, Graham R. Allan, William E. Hasselbrack, Clark J. Weaver, and Edward V. Browell. “Airborne measurements of CO2 column concentration and range using a pulsed direct-detection IPDA lidar.” Remote Sensing 6, no. 1 (2014): 443-469.
See newly added table at bottom of post showing summary from the above reference.
CO2 concentration depends upon geography because of surface production or absorption. In the case of Iowa, it’s agriculture.
Tropopause is generally accepted to be about 10 km.