Sensors cut cost of air monitoring

A new instrument developed by researchers at University College London looks set to make low-cost monitoring of air quality and land contamination a reality.

The device – which could also be installed in vehicle ventilation systems, allowing drivers to choose whether to recirculate cabin air or draw in fresh sources from outside – uses sensors to identify the concentration of combustible gases in the air.It takes in air, which passes over absorbent pellets covering a large surface area, coating them with any pollutants suspended within it.

The pellets are then heated, releasing the gas across the special sensor, which measures its resistance, said Dr Daren Caruana, lecturer in chemistry at UCL, who worked as a post-doctoral student on the project. ‘The system could have great implications for the way the environment is managed,’ he said.

The process measures the precise level of noxious substances, while giving a basic indication of its species.

These include chemicals such as toluene, heptane, xylene and benzene, from sources including vehicle exhausts and pollutants leaching into groundwater from waste sites.At present, because of the high cost of traditional air quality monitors such as mass spectrometers and gas chrom- atographs, which cost around £100,000 each, hydrocarbon measuring is limited to just 13 locations across the UK.

Mass spectrometers determine the constituents of a gas by ionising it and seeing how far particles travel in a vacuum chamber. Gas chromatographs contain a heated coil to which some constituents are more likely to stick than others, enabling scientists to identify a gas compound by the speed it travels down the tube.

Both instruments require trained personnel to operate them and are large, expensive and unwieldy, unlike the new sensor-based device, which its developers estimate should sell for around £500 to £1,000.

This means a number of monitors could be placed throughout a city, or in locations surrounding a waste tip to measure contamination and its spread, said Caruana. ‘In theory each monitor can be connected with mobile technologies, sending in its position and readings to a central point every 40 minutes.’

The technology cannot give a precise identification of the chemicals it encounters, but it can achieve sensitivities of 0.1 parts per billion by volume, in an analysis time of about 40 minutes, he said.

As well as measuring compounds that cause smog in urban air or solvents from sources such as underground petrol tanks, the device has the potential to detect and measure chemicals given off by new materials such as carpets installed when an office is refurbished, said Caruana.

‘Some chemicals cannot be detected by smell, but can affect staff,’ he added. ‘Using this instrument you could make sure that levels were safe before they were allowed back in.’

The research was led by UCL’s Prof David Williams, who also helped to set up Portsmouth-based firm Capteur Sensors, developer of the sensors.

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