We present a newly developed instrument for ²²Na-based positron-annihilation lifetime spectroscopy, designed to facilitate the simultaneous control of temperature, gas atmosphere, and humidity in a single experimental system. The spectrometer operates within a temperature range of 50-480 K and pressures from 10⁻⁶ mbar to 1.5 bars. It features a novel gas dosing chamber that allows in situ adsorption studies with gases such as but not limited to CO₂, N₂, Ar, O₂, and their mixtures, with precise control over mixing ratios. Additionally, the device supports in situ humidity exposure, allowing for comprehensive studies of sample interactions with both humidity and humid gases. Fully automated, the system provides seamless data acquisition and environmental control, including pressure and temperature regulation. We demonstrate the instrument’s capability to elucidate alterations in the free volume of maltodextrin under humidity exposure. Additionally, we illustrate the instrument’s efficacy through case studies on CPO-27 metal-organic frameworks (MOFs), highlighting its versatility in analyzing adsorption phenomena across diverse gas adsorbates and temperatures. This state-of-the-art spectrometer stands as an indispensable tool for probing the physicochemical attributes of materials under varying conditions, providing pivotal insights into gas adsorption mechanisms and material dynamics.