Air quality in aircraft: A continuing debate

In this issue, we are reminded of the diverse range of indoor environments that are very different in type, function and location, and yet all aim to provide protection for occupants from the outside environment and as far as possible maintain internal conditions appropriate for their health and well being. These environments range from naturally ventilated homes polluted by use of biomass fuels to those created and maintained by advanced technology in spacecraft. While public transport via space travel may become a reality in the coming decades, currently air travel takes place in the lower and upper atmosphere and is a regular activity both for leisure and work. During 2014, commercial airlines transported 3.3 billion passengers (plus 50 million metric tons of cargo) by means of a global fleet of over 25,000 aircraft undertaking 99,700 flights per day. Within Europe, the air traffic control network handles 27,000 flights and 2.27 million passengers per day, and this is expected to grow annually, for example, the aviation traffic in Europe is predicted to reach 14.4 million flights in 2035 (50% more than in 2012). Commercial transport aeroplanes operate in an external environment that is hostile to human life. Ambient conditions outside the aircraft include very cold temperatures ( 43 C to 65 C), very dry air, too low a level of partial pressure of oxygen to sustain life, periodic episodes of high ozone, pockets of air turbulence and levels of cosmic radiation approximately 100 times higher at typical cruise altitudes than it is at ground level. The environment inside the aircraft cabin must be healthy, safe and comfortable for passengers and crew within the constraints of aeroplane design and function. The aircraft’s environmental control system (ECS) regulates these conditions, and when at high altitude, the cabin is pressurised to an altitude equivalent to between 6000 and 8000 feet (i.e. 1800 to 2400m) above sea level. The humidity of the cabin air tends to be low compared with other public indoor spaces and occupants experience continuous noise, vibration and accelerations. Aircraft passenger cabins provide the smallest available volumes per person of any enclosed public spaces. Particular health concerns associated with health travel include those that have been associated with air quality, infection, radiation, pressure (including deep vein thrombosis), ergonomics, noise and vibration. With respect to air quality experienced by the traveller, air pollution within and around airports is an issue gaining increasing prominence with respect to the impact on the health and well being of both workers and passengers as well as those living nearby. There are various sources of air pollution in an airport which include ground vehicular traffic, ground service equipment, maintenance work, heating facilities, fugitive vapours from refuelling operations, kitchens and restaurants (for passengers and operators), intermodal transportation systems and road traffic (e.g. passenger cars, buses, taxis and goods vehicles). The pollutants of concern involved with aircraft emissions include particulate matter (PM), nitrogen and sulphur oxides (NOx, SOx), carbon dioxide (CO2), carbon monoxide (CO), volatile organic compounds (VOCs), and ozone (O3). Exceedance of ambient air quality regulations because of emissions associated with airport activities is a factor determining expansion of existing and the siting of new airports. Passengers and crew will be exposed to these pollutants on arrival, waiting and boarding aircraft. Once on board and in flight, passengers and crew are within a very airtight structure with full mechanically controlled ventilation, and contaminants present outside will be drawn into the cabin as components of the air supply. Measurements of air quality in cabins of aircraft preparing for take-off and taxiing following landing have been shown to have elevated levels of pollutants associated with fuel combustion, such as ultrafine particulates, compared with concentrations measured during flight when the intake air is not polluted by these components.