An eye on emissions

An eye on emissions

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Manchester, UK, October 02, 2007: As EU limits on air quality threaten airport expansion, a UK university team has developed laser radar technology to produce a reliable estimate of aviation pollution and better understand how it acts on and around the runways.

Dr Michael Bennett at Manchester Metropolitan University’s Centre for Air Transport and the Environment is leading the project. His team replicated technology used in the US to create their own ‘eye-safe’ Light Detection and Ranging (LIDAR) device to track aircraft emissions. The team is the first in Europe to use this method to measure airport aircraft emissions.

The LIDAR reflects beams of light off nitrogen oxides and particulates in the air, measuring their shape and position, but not their concentration. It also has the ability to rapidly scan in elevation and azimuth, enabling it to track an aircraft and its emissions.

‘This particular system was developed as a mobile system to measure dispersion at power stations. Originally we put in a crystal which doubled the frequency and took it into the infrared range which was visible but very far from ‘eye-safe’. Ideal for measuring around power stations but not exactly something we could point at an aircraft as it took off and landed,’ said Bennett. ‘I then heard of someone in the US who tripled the frequency using two crystals. This took the wavelength to 355nm, in the UV range. At this range all of the optics work but it doesn’t penetrate the eye’ added Bennett.

One of the main issues the team had to take into account was the vortices formed when an aircraft takes off and lands. When on the ground and the engines are running ready for take off, the heat of the emissions mean they rise, but the vortices formed as the aircraft lifts or descends pushes the emissions downwards, potentially increasing their impact. The vortices are streaks of air which form from the tips of the wings and follow the aircraft, forming a large area of descending air. This air then drives the emissions downward, increasing the ground levels in the local area.

The team was originally funded by the Department of Transport to take measurements at Heathrow and is now carrying out further tests at Manchester airport backed by the EPSRC. The DoT forecasts a five to seven per cent rise in air traffic needed to meet demand, but EU statutory limits on emissions could prove to be a major barrier to airport expansion. Bennett believes levels of NO2 and particulates, such as PM10, could be a ‘show stopper’ for the third runway at Heathrow and a second at Manchester.

After using the LIDAR for various projects Bennett believes it has the potential for measuring other factors. He believes that with some delicate calibration the device could also measure emission concentration. ‘You could argue we’re halfway through a 10-year programme,’ said Bennett. ‘If we could get it to work with CO2, it would be a major breakthrough.’