Issues Affecting Air Quality

Local air quality is a limiting factor in the development of many airports. In particular, the EU limit value for NO2 of 40 μg/m³ as an annual mean; that for PM10 will be of 20 μg/m³ , which is valid since January 1, 2010. Ambient concentrations at many European airports are already close to, or above these values.  There is as yet no EU limit value for PM2.5, but neither is there yet any evidence of a safe threshold; epidemiological studies in the US suggest that an extra 1 μg/m³ reduces mean life expectancy by l2 months. If air traffic is to continue to increase in Europe, its impact on local air quality will have to be better understood and cleaner modes of operation developed.

ECATS has the capability to study many of the issues determining local air quality:

• The dispersion of material from aero-engines is qualitatively different from that from a fixed industrial source: the emitted plume has significant momentum and buoyancy, while the source is moving and accelerating. We can characterize these processes using remote sensing techniques such as scanning Lidar or DOAS.
• NO2 is both a primary and secondary pollutant. We can sample the primary emission close to the engine using a traversing rake and measure concentrations further out using DOAS or point samplers.
• It is most probably the fine, non-volatile aerosol that has the greatest relevance for health effects. Aerosol evolves continuously from the point of emission, as it mixes with the ambient air. We can measure this process and seek appropriate measures for characterizing emissions.
• Aero-engine exhausts contain many other potentially hazardous organic components, particularly when an engine is operating at low thrust. We have the capability to measure and speciate such emissions.
• There are many sources of air pollution associated with an airport other than aero-engines: tyre smoke on landing; ground-service vehicles; volatile organics from fuelling operations; road traffic from passengers and staff, etc. We can measure the impact of such emissions and to some extent attribute ambient concentrations to particular sources.

All such measurements must be fitted into theoretical and numerical models so that today’s airports can be extrapolated to tomorrows. Thus, we can develop dynamical models of the dispersion of aircraft emissions, which may then be included in regulatory models of local air quality impact. Likewise, micro-physical and chemical models can describe how the primary emissions of an aircraft evolve into the secondary emissions that are relevant to what the neighbours of the airport may have to breathe. Similarly, operational studies can illuminate how changes in management practice (e.g. more efficient control of taxiing) may impact upon local air quality.