Carbon dioxide capture in porous materials faces two challenges: adsorption temperature and the presence of water vapor. Direct air capture of CO2 benefits from both lower temperatures and low humidity, hence the proclivity for locating DAC installations in arid and/or cold regions - such as extreme northern climates or deserts. This presentation considers experimental challenges and solutions for measuring isotherms of both referenced vapors on a suitable adsorbent at target temperatures as low as -20C. Experimental data demonstrating water vapor isotherms as low as 0.1% RH and CO2 below 1ppm will be presented.