AETIAQ: Aviation emissions and their impact on air quality
Dr Angus Graham
Emissions produced at airports affect the level of pollutants in neighbouring areas. Air quality is impacted by a variety of airport sources, with pollutants being emitted by aircraft, airside service vehicles, power and heating plants, and road traffic accessing or servicing the airport. One of the objectives of this study is to improve the methodologies for assessing the contribution of aircraft. In their take-off run, aircraft constitute a strong but intermittent source of emissions, making it difficult to establish their impact on mean pollutant concentrations nearby. This lack of
understanding greatly hinders airports who need to develop air-pollution mitigation
A series of field measurements were carried out on a passenger jet aircraft at Cranfield University. The dispersion and evolution of emissions released from the aircraft’s engines as it executes take-off and landing operations will be measured using a range of techniques.
Complementary series of studies took place at British Airways Engineering at
Heathrow Airport where an aircraft in maintenance had their engines test run through a range of power settings in a noise-suppressing pen. This standardised environment will allow a set of repeatable air-quality measurements to be obtained over a range of aircraft types. Data collected will complement a large set of physical and chemical measurements on exhaust plumes from aircraft obtained over the last two years at Heathrow and Manchester Airports.
A measurement campaign at Cranfield and Manchester Airports has yielded an extensive set of simultaneous physical and chemical measurements on the evolution of exhausts from aircraft embarking on takeoff. At Cranfield A BAe146 moving under the direction of experimenters was studies. A novel passive imaging spectometer was consutrcted and deployed so as to establish the concentration of NO2 in exhausts as integrated along skyward lines of sight, according to the signature of the has in naturally-scattered sunlight. An imaging UV Lidar aimultaneously measured the backscattering from exhaust aerosol. Remote and rapid measurements on the concentration and transport of exhaust pollutants were thus obtained, conveniently and safely, and sufficiently far from aircraft as to lie beyond airport security fencing.
The Lidar captures the scattering from aerosol throughout sections through exhaust plumes. The images show that within about a wingspan downstream of an aircraft embarking on takeoff, exhaust streams from engines merge to form a common plume that tends to hug the ground. (The relatively high wing and engine height of the 146 us thus quickly rendered unimportant.) Statistics on the width and vertical extent of the young plume concur with those described for wall jets in the literature. The exhausts may thus be supposed too young to have acquired significant upward momentum from their buoyancy. Older exhausts may also be observed, to upwards of a minute after the 146 moves off, though their weak scattering makes it difficult to obtain reliable statistics on their dispersion.
The spectroscopy captures NO2 in exhausts both from idling engines and when takeoff power is realised. HONO is also detectable in sginificant quantities, as is though to form in heterogenous reactors of NO2 with plume aurosol. When the 146 is powered up statically for takeoff, concentration of NO2 as integrated over a path across the release are observed to tend to equilibrate, over some 30-130m from engines. A characteristic trend value of 1.6×1016 molecules NO2 cm-2 may be identified. On comparison with predictions made on taking exhausts to reside in a wall jet, this is consistent with about 6% of NOx molecules being in the form of NO2. The speciation of NOx in this part of the plume thus appears comparable to that reported in the literature in the case of the primary emissions
practicality of Lidar
spectroscopic methods in observing aircraft emissions at commercial airports
Both techniques yield informative images over a continuum of ranges and angles.A dataset has been obtained which should aid and stimulate the further development of air-quality models for regulatory purposes.
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