Ozone creates irritant in aircraft cabin air

Ozone in the cabins of aircraft reacts with organic compounds derived from passengers, their clothing and their carryon luggage to produce potentially harmful compounds, say US researchers. Earlier work by the same scientists using simulated aircraft cabins had shown that common indoor pollutants like cleaning agents and scents reacted with ozone to form formaldehyde, organic acids, aldehydes and ketones. Now, the study has been extended to real aircraft during trans-US and intercontinental flights, as they described in Environmental Science and Technology.

Most of the planes did not have scrubbers to remove the ozone from the cabin atmosphere as it enters from the outside. The maximum levels of ozone were higher in spring and summer compared with autumn and winter and peak concentrations exceeded 100 ppb in some cases. In Boeing 747s with ozone converters, the ozone levels in the majority of the flights were the same as those in flights without converters, presumably due to the diminishing performances of the devices. This is an important finding given the health effects of ozone.

The straight-chain aldehydes from C6-C10 were all detected by GC/MS, along with 6-methyl-5-hepten-2-one (HMO). Decanal is likely the product of ozone with unsaturated fatty acids, which are components of human skin oil. HMO is derived from ozone and squalene, also found in skin oils, and its variations with cabin occupancy levels seem to confirm that skin oil is the main source. Modelling studies suggested that there were other sources of the some of the aldehydes found in the air, which could be passenger clothing, luggage and personal care products.

HMO is known to react further to produce 4-oxopentanal, a known irritant and sensitiser. At the HMO levels detected, 4-oxopentanal is likely to have been formed, but it was not measured in this work. The research team advised that a method for monitoring it routinely on aircraft should be developed, so that passenger exposure and safety can be assessed.