Gas-sensing detector gets measure of toxic gasses

This new air quality monitoring system uses laser technology to detect the smallest amount of toxic gasses in large, densely populated regions.

With multiple sensors connected to form a gas analysing network, the units can spot trace amounts of numerous gasses – including nitrogen dioxide (NO2), sulphur dioxide (SO2), carbon monoxide (CO), ozone (O3), and particulate matter – in real-time in dynamic environments.

The World Health Organisation estimates that 4.2 million people die prematurely from the high levels of toxic gas molecules and particulate matter they inhale from ambient air pollution.

Currently, methods for assessing air quality in urban environments rely on expensive, refrigerator-sized units. Low-cost sensors rely on chemical reactions, which are inaccurate and can give false readings.

The €6.9m PASSEPARTOUT project aims to provide a compact detector with a complete understanding of the types and concentrations of toxic gases at a cost of under €1,000.

In a statement, PASSEPARTOUT project coordinator Dr William Whelan-Curtin said: “The miniature PASSEPARTOUT hyperspectral optical-based sensors will provide a comprehensive approach to understanding urban air quality. To have a widespread network and to take meaningful steps towards a smart city, current, expensive methods are not feasible.

“At present, accurate assessments of urban air are difficult. Air quality varies significantly over time, over short distances and across different areas within a city. Traditional monitoring methods struggle to capture these nuanced variations adequately. We are working to provide a system with high precision and excellent spatial resolution to detect NOx, SO2, NH3, CH4, CO, CO2, and black carbon.”

The system works using photothermal and photo-acoustic effects. When the laser light hits a toxic gas, the molecule absorbs light energy, giving off a heat ‘signature’ that is then reported back to the system that identifies what the harmful gas is, and how much of it is present.

The PASSEPARTOUT also incorporates quartz tuning fork technology, or Quartz Enhanced Photo-Acoustic Spectroscopy (QEPAS).

Dr Whelan-Curtin said: “QEPAS is particularly useful for the detection and quantification of trace gases in challenging environments. We use a quartz tuning fork with a sharp mechanical resonance to detect the signals generated by the gas sample while suppressing the background noise. This tuning fork detects the acoustic waves generated by the gas as it heats and cools. The signal is then analysed to determine the concentration of the target gas. The exact wavelengths of the laser, or lasers, can be tuned to match the characteristic absorption spectrum of the target gas, meaning our system categorically detects specific gases, like carbon monoxide or sulphur dioxide.”

The PASSEPARTOUT team is trialling their technology in landfill sites, seaports, at the University of Bari, Italy,  and in a selection of schools in Cork, Ireland.

“As part of the project, we are developing a smartphone app to check air quality in real-time,” said Dr Whelan-Curtin. “In the future, we hope this can be integrated into Google Maps so that your journey to and from work or school can show you not just traffic hotspots but also the route with the cleanest air.”