Effect of charcoal equipped HEPA filters on cabin air quality in aircraft. A case study including smell event related in-flight measurements

Cabin air quality (CAQ) of aircraft is an important issue for both comfort and safety of occupants during flight. Due to high impact of carbon dioxide a high ventilation rate in the aircraft cabin is essential for life saving. However, external and internal sources of potential pollutants may also affect the CAQ. Subjective smell perception occasionally results in guidelines-regulated actions by pilots, independent of the real chemical burden. Installation of novel filtration units is presumed to improve CAQ and to reduce smell. The present study aimed to investigate the CAQ on Airbus A321 aircraft equipped with a charcoal filter in addition to the standard high efficiency particulate air filter. Overall, a reduction of approx. 30% was observed for (S)VOCs in the study. For the first time, a reported “smell event” and diversion of the aircraft was accompanied with comprehensive measurements, yet without detection of noticeable amounts of pollutants. During another flight connected with a de-icing procedure on ground, elevated levels of various pollutants were measured in the cabin air. Despite subjective perception of smell and measurement of unusually high levels of VOCs and aldehydes in the cabin air, no complaints about CAQ had been reported by the crewmembers during this flight. These diametric cases suggest that decision-making by the crewmembers during flights may not always be supported by experimentally generated data. Subjective perception alone of uncommon smell may not be a reliable indicator of harmful or toxic chemical pollution in aircraft and should not be used for decision-making.