Researchers from King Abdullah University of Science and Technology (KAUST) have developed a laser-based device capable of sensing extremely low concentrations of benzene. The sensor works in real time, helping monitor benzene emission levels. The sensor, developed by a team led by Aamir Farooq, features walls that consist of two parallel, concave mirrors. The mirrors are positioned to face one another, forming a cavity around a gas sample. The cavity traps a laser beam, which repeatedly reflects off the mirrors. The two-mirror system enables the laser beam to travel across a distance (through the sample) that is significantly larger than the distance it would travel in a system featuring inter-mirror separation. The system ultimately allowed scientists to detect benzene concentrations that were three orders of magnitude lower than in a conventional sensor. A precisely controlled laser wavelength and the mathematical elimination of any interference from methane, ethylene, and water vapor allowed the team to optimize the extent to which the sensor absorbed light. The controls provided accurate benzene concentrations even in the presence of interfering components. KAUST researchers have developed a laser-based sensor that could improve monitoring of benzene emissions and limit exposure to this pollutant. Courtesy of Anastasia Serin via KAUST. Benzene exposure can cause cancer, as well as aplastic anemia — a condition in which the body fails to naturally produce a necessary number of new blood cells. The chemical is commonly found in industrial settings, such as crude oil processing facilities and even service stations. It is also found in biomass-based heating fuels. Existing approaches and methods for controlling benzene emissions rely on gas chromatography and mass spectrometry. Sampling protocols involved in those methods can be time-consuming, though, and, the KAUST team reports, are plagued by the type of ambient air-caused interference that the new sensor overcomes. Detection limits can also exceed 100 parts per billion (ppb). The KAUST laser-based sensor exhibited high selectivity and sensitivity to benzene with a detection limit of 2 ppb. Without requiring preliminary calibration, it successfully performed measurements in seconds. “The sensor could be attached to a drone or carried by hand to scan target areas daily for benzene emissions,” said Mhanna Mhanna, who performed many of the experiments on the sensor at KAUST as part of the project. The team reported that it is actively examining ways to increase sensor portability. In testing, the sensor detected trace concentrations of benzene in a parking garage on weekdays, compared to one weekend — demonstrating a potential common application for the new device. The project was funded by Saudi Aramco’s Environmental Protection Department. The research was published in IEEE Sensors Journal (www.doi.org/10.1109/JSEN.2020.3026981).