Air Quality In Airport Approaches: Impact Of Emissions From Aircraft In Ground Run and Flight

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Development of infrastructure and the urban environment must be carefully managed if it is not to jeopardise air quality. To satisfy planning statutes and national and international directives, the impact of a major airport development on air quality as well as noise levels must be assessed (e.g. as in the cases of Manchester Airport 2 d Runway and T5 Heathrow). Nitrogen oxides (NO.) and particulates are emitted in the exhaust streams of aircraft, road and service vehicles and power and heating plants, and may adversely affect human health and the environment. The recent White Paper on aviation ('The Future of Air Transport', DfT, 2003) foresees that a 5-7% mean annual increase in air-traffic movements is needed to meet demand, but with only limited scope for reducing emissions from jet engines, it appears quite possible that airport capacity in the UK may become constrained by air-quality requirements. The most difficult issue facing the construction of a third runway at Heathrow, for example, is meeting statutory EU limits on NO2.Emissions from aeroplanes disperse as a result of processes additional to those active in the ambient atmosphere. A lateral diffusion is effected in the aeroplane wake. When the aeroplane is out of ground-effect, a pair of streamwise wingtip vortices rolls up in the wake and entrains emissions. An aeroplane exerts a downward force on the air, and so the wake must descend, as mediated through the action of the vortices on one another. The vortices thus relay emissions to the ground, far more efficiently than would otherwise occur through ambient processes alone. In the ground run of aeroplanes, in contrast, vortex formation is impeded, and a buoyant rise of hot exhausts may take place later instead.For local concentrations due to aircraft to be predicted accurately, it is necessary to develop innovative measurement and modelling techniques that take account of these complicating factors. Predictions holding both instantaneously and in the mean, and as a function of aircraft departure frequencies and meteorological conditions, are needed. A novel kinematic model of the vortex-mediated transport of NO, was developed recently to this end, under EPSRC funding (Graham and Raper, Grant GR/R91649/01). It is proposed here to develop an eye-safe Lidar system at the University of Manchester Institute of Science and Technology (UMIST), and deploy it in an experiment at a major civil airport (that of Manchester). Particulates and aerosols in the aircraft exhausts will cause a backscattering of the Lidar beam. The capacity to sweep the beam rapidly in either the elevation or azimuth will exist, yielding near-instantaneous spatial maps of the scattering. Supporting spectroscopic data will be obtained remotely by UMIST and Cambridge University, revealing NO, concentrations integrated along both horizontal and vertical lines of sight. The data will be used to validate the vortex-transport model, and to reveal the characteristics of the dispersion from aircraft in ground-effect.