Beyond the Odor: Targeting the Root Cause of Air Conditioning VOC Pulse Release for Next-Generation Indoor Air Quality

Amid rising global temperatures and the growing demand for air conditioning (AC), reports of transient sour and foul odors are also increasing. Using a novel combination of PTR-TOF-MS and FTIR in laboratory simulations, this study found that shifting AC operation from 16 to 26 °C triggers a rapid pulse release of key OCs, including acetaldehyde, acrolein, acetone, acetic acid, acrylic acid, and propionic acid. Concentrations surged within 5 min (e.g., acetic acid rose 11.06 ppbv), peaked around 12 min (19.20 ppbv), and stabilized after approximately 16 min. Total acetic acid emitted in the first 5 min was 736.18 μg. The primary sources were hydrophilic top coatings, whose VOC emission profiles correspond to operational odors under specific thermo-humidity conditions. Secondary sources included acrylic sealants, which released temperature-dependent acids such as acrylic acid, and filter modules, which partially reduced odors via adsorption. The underlying mechanism is described as “low-temperature condensation and enrichment followed by thermally-induced pulse release” driven by variations in the temperature and humidity. Subsequent optimization cut key VOCs within 5 min, achieving 100% propionic acid and 99.88% acetic acid reduction. This work elucidates the physics-driven origin of AC odors, paving the way for next-generation odor-free AC through source-control engineering.